TI LM3444

LM3444
LM3444 AC-DC Offline LED Driver
Literature Number: SNVS682B
LM3444
AC-DC Offline LED Driver
General Description
Features
The LM3444 is an adaptive constant off-time AC/DC buck
(step-down) constant current controller that provides a constant current for illuminating high power LEDs. The high frequency capable architecture allows the use of small external
passive components. A passive PFC circuit ensures good
power factor by drawing current directly from the line for most
of the cycle, and provides a constant positive voltage to the
buck regulator. Additional features include thermal shutdown,
current limit and VCC under-voltage lockout. The LM3444 is
available in a low profile MSOP-10 package or an 8 lead SOIC
package.
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Application voltage range 80VAC – 277VAC
Capable of controlling LED currents greater than 1A
Adjustable switching frequency
Low quiescent current
Adaptive programmable off-time allows for constant ripple
current
Thermal shutdown
No 120Hz flicker
Low profile 10 pin MSOP package or 8 lead SOIC package
Patent pending drive architecture
Applications
■ Solid State Lighting
■ Industrial and Commercial Lighting
■ Residential Lighting
Typical LM3444 LED Driver Application Circuit
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30127501
© 2011 Texas Instruments Incorporated
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LM3444 AC-DC Offline LED Driver
November 17, 2011
LM3444
Connection Diagrams
Top View
Top View
30127503
8-Pin SOIC
NS Package Number M08A
30127573
10-Pin MSOP
NS Package Number MUB10A
Ordering Information
Order Number
Spec.
Package Type
NSC Package
Drawing
Top Mark
Supplied As
LM3444MM
NOPB
MSOP-10
MUB10A
SZTB
1000 Units, Tape and Reel
LM3444MMX
NOPB
MSOP-10
MUB10A
SZTB
3500 Units, Tape and Reel
LM3444MA
NOPB
SOIC-8
M08A
LM3444MA
95 Units, Rail
LM3444MAX
NOPB
SOIC-8
M08A
LM3444MA
2500 Units, Tape and Reel
Pin Descriptions
MSOP
SOIC
Name
1
1
Description
NC
No internal connection. Leave this pin open.
2
NC
No internal connection. Leave this pin open.
3
NC
No internal connection. Leave this pin open.
4
8
COFF
OFF time setting pin. A user set current and capacitor connected from the output to this pin sets
the constant OFF time of the switching controller.
5
2
FILTER
Filter input. A low pass filter tied to this pin can filter a PWM dimming signal to supply a DC
voltage to control the LED current. Can also be used as an analog dimming input. If not used for
dimming connect a 0.1µF capacitor from this pin to ground.
6
3
GND
Circuit ground connection.
7
4
ISNS
LED current sense pin. Connect a resistor from main switching MOSFET source, ISNS to GND
to set the maximum LED current.
8
5
GATE
Power MOSFET driver pin. This output provides the gate drive for the power switching MOSFET
of the buck controller.
9
6
VCC
Input voltage pin. This pin provides the power for the internal control circuitry and gate driver.
10
7
NC
No internal connection. Leave this pin open.
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2
If Military/Aerospace specified devices are required,
please contact the Texas Instruments Sales Office/
Distributors for availability and specifications.
VCC and GATE to GND
ISNS to GND
FILTER and COFF to GND
COFF Input Current
Continuous Power Dissipation
(Note 2)
-0.3V to +14V
-0.3V to +2.5V
-0.3V to +7.0V
60mA
Internally Limited
2 kV
150°C
-65°C to +150°C
260°C
Operating Conditions
VCC
Junction Temperature
8.0V to 13V
−40°C to +125°C
Electrical Characteristics
Limits in standard type face are for TJ = 25°C and those with boldface type apply
over the full Operating Temperature Range ( TJ = −40°C to +125°C). Minimum and Maximum limits are guaranteed through test,
design, or statistical correlation. Typical values represent the most likely parametric norm at TJ = +25ºC, and are provided for
reference purposes only. Unless otherwise stated the following conditions apply: VCC = 12V.
Symbol
Parameter
Conditions
Min
Typ
Max
Units
1.58
2.25
mA
7.4
7.7
V
1.327
V
VCC SUPPLY
IVCC
VCC-UVLO
Operating supply current
Rising threshold
Falling threshold
6.0
Hysterisis
6.4
1
COFF
VCOFF
Time out threshold
RCOFF
Off timer sinking impedance
1.225 1.276
33
tCOFF
Restart timer
180
60
Ω
µs
CURRENT LIMIT
VISNS
ISNS limit threshold
tISNS
Leading edge blanking time
1.174 1.269
Current limit reset delay
ISNS limit to GATE delay
ISNS = 0 to 1.75V step
1.364
V
125
ns
180
µs
33
ns
CURRENT SENSE COMPARATOR
VFILTER
FILTER open circuit voltage
RFILTER
FILTER impedance
VOS
720
750
780
1.12
Current sense comparator offset voltage
-4.0
mV
MΩ
0.1
4.0
mV
0.24
0.50
V
0.50
GATE DRIVE OUTPUT
VDRVH
GATE high saturation
IGATE = 50 mA
VDRVL
GATE low saturation
IGATE = 100 mA
0.22
IDRV
Peak souce current
GATE = VCC/2
-0.77
Peak sink current
GATE = VCC/2
0.88
Rise time
Cload = 1 nF
15
Fall time
Cload = 1 nF
15
(Note 4)
165
tDV
A
ns
THERMAL SHUTDOWN
TSD
Thermal shutdown temperature
Thermal shutdown hysteresis
°C
20
THERMAL SPECIFICATION
RθJA
MSOP-10 junction to ambient
124
RθJC
MSOP-10 junction to case
76
°C/W
Note 1: Absolute maximum ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions for which the device is intended
to be functional, but device parameter specifications may not be guaranteed. For guaranteed specifications and test conditions, see the Electrical Characteristics.
All voltages are with respect to the potential at the GND pin, unless otherwise specified.
Note 2: Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at TJ = 165°C (typ.) and disengages at TJ
= 145°C (typ).
Note 3: Human Body Model, applicable std. JESD22-A114-C.
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LM3444
ESD Susceptibility
HBM (Note 3)
Junction Temperature (TJ-MAX)
Storage Temperature Range
Maximum Lead Temp.
Range (Soldering)
Absolute Maximum Ratings (Note 1)
LM3444
Note 4: Junction-to-ambient thermal resistance is highly application and board-layout dependent. In applications where high maximum power dissipation exists,
special care must be paid to thermal dissipation issues in board design. In applications where high power dissipation and/or poor package thermal resistance is
present, the maximum ambient temperature may have to be derated. Maximum ambient temperature (TA-MAX) is dependent on the maximum operating junction
temperature (TJ-MAX-OP = 125°C), the maximum power dissipation of the device in the application (PD-MAX), and the junction-to ambient thermal resistance of the
part/package in the application (RθJA), as given by the following equation: TA-MAX = TJ-MAX-OP – (RθJA × PD-MAX).
Typical Performance Characteristics
fSW vs Input Line Voltage
Efficiency vs Input Line Voltage
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VCC UVLO vs Temperature
Min On-Time (tON) vs Temperature
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LM3444
Off Threshold (C11) vs Temperature
Normalized Variation in fSW over VBUCK Voltage
1.29
VOFF (V)
1.28
1.27
1.26
OFF Threshold at C11
1.25
-50 -30 -10 10 30 50 70 90 110130150
TEMPERATURE (°C)
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Leading Edge Blanking Variation Over Temperature
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LM3444
Simplified Internal Block Diagram
30127511
FIGURE 1. Simplified Block Diagram
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Theory of Operation
Refer to Figure 2 below which shows the LM3444 along with
basic external circuitry.
FUNCTIONAL DESCRIPTION
The LM3444 contains all the necessary circuitry to build a linepowered (mains powered) constant current LED driver.
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FIGURE 2. LM3444 Schematic
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LM3444
Application Information
LM3444
charged. However, the network of diodes and capacitors
shown between D3 and C10 make up a "valley-fill" circuit. The
valley-fill circuit can be configured with two or three stages.
The most common configuration is two stages. Figure 3 illustrates a two and three stage valley-fill circuit.
VALLEY-FILL CIRCUIT
VBUCK supplies the power which drives the LED string. Diode
D3 allows VBUCK to remain high while V+ cycles on and off.
VBUCK has a relatively small hold capacitor C10 which reduces
the voltage ripple when the valley fill capacitors are being
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FIGURE 3. Two and Three Stage Valley Fill Circuit
The valley-fill circuit allows the buck regulator to draw power
throughout a larger portion of the AC line. This allows the capacitance needed at VBUCK to be lower than if there were no
valley-fill circuit, and adds passive power factor correction
(PFC) to the application.
pacitors are placed in parallel to each other (Figure 5), and
VBUCK equals the capacitor voltage.
VALLEY-FILL OPERATION
When the “input line is high”, power is derived directly through
D3. The term “input line is high” can be explained as follows.
The valley-fill circuit charges capacitors C7 and C9 in series
(Figure 4) when the input line is high.
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FIGURE 5. Two stage Valley-Fill Circuit when AC Line is
Low
A three stage valley-fill circuit performs exactly the same as
two-stage valley-fill circuit except now three capacitors are
now charged in series, and when the line voltage decreases
to:
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FIGURE 4. Two stage Valley-Fill Circuit when AC Line is
High
The peak voltage of a two stage valley-fill capacitor is:
Diode D3 is reversed biased and three capacitors are in parallel to each other.
The valley-fill circuit can be optimized for power factor, voltage hold up and overall application size and cost. The
LM3444 will operate with a single stage or a three stage valley-fill circuit as well. Resistor R8 functions as a current
limiting resistor during start-up, and during the transition from
series to parallel connection. Resistors R6 and R7 are 1 MΩ
bleeder resistors, and may or may not be necessary for each
application.
As the AC line decreases from its peak value every cycle,
there will be a point where the voltage magnitude of the AC
line is equal to the voltage that each capacitor is charged. At
this point diode D3 becomes reversed biased, and the ca-
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30127523
FIGURE 6. LM3444 Buck Regulation Circuit
the ISNS pin. This sensed voltage across R3 is compared
against the voltage of FILTER, at which point Q2 is turned off
by the controller.
OVERVIEW OF CONSTANT OFF-TIME CONTROL
A buck converter’s conversion ratio is defined as:
Constant off-time control architecture operates by simply
defining the off-time and allowing the on-time, and therefore
the switching frequency, to vary as either VIN or VO changes.
The output voltage is equal to the LED string voltage (VLED),
and should not change significantly for a given application.
The input voltage or VBUCK in this analysis will vary as the
input line varies. The length of the on-time is determined by
the sensed inductor current through a resistor to a voltage
reference at a comparator. During the on-time, denoted by
tON, MOSFET switch Q2 is on causing the inductor current to
increase. During the on-time, current flows from VBUCK,
through the LEDs, through L2, Q2, and finally through R3 to
ground. At some point in time, the inductor current reaches a
maximum (IL2-PK) determined by the voltage sensed at R3 and
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FIGURE 7. Inductor Current Waveform in CCM
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LM3444
voltage, transistor Q2 is turned off and diode D10 conducts
the current through the inductor and LEDs. Capacitor C12
eliminates most of the ripple current seen in the inductor. Resistor R4, capacitor C11, and transistor Q3 provide a linear
current ramp that sets the constant off-time for a given output
voltage.
BUCK CONVERTER
The LM3444 is a buck controller that uses a proprietary constant off-time method to maintain constant current through a
string of LEDs. While transistor Q2 is on, current ramps up
through the inductor and LED string. A resistor R3 senses this
current and this voltage is compared to the reference voltage
at FILTER. When this sensed voltage is equal to the reference
LM3444
During the off-period denoted by tOFF, the current through L2
continues to flow through the LEDs via D10.
THERMAL SHUTDOWN
Thermal shutdown limits total power dissipation by turning off
the output switch when the IC junction temperature exceeds
165°C. After thermal shutdown occurs, the output switch
doesn’t turn on until the junction temperature drops to approximately 145°C.
With efficiency of the buck converter in mind:
Design Guide
Substitute equations and rearrange:
DETERMINING DUTY-CYCLE (D)
Duty cycle (D) approximately equals:
Off-time, and switching frequency can now be calculated using the equations above.
With efficiency considered:
SETTING THE SWITCHING FREQUENCY
Selecting the switching frequency for nominal operating conditions is based on tradeoffs between efficiency (better at low
frequency) and solution size/cost (smaller at high frequency).
The input voltage to the buck converter (VBUCK) changes with
both line variations and over the course of each half-cycle of
the input line voltage. The voltage across the LED string will,
however, remain constant, and therefore the off-time remains
constant.
The on-time, and therefore the switching frequency, will vary
as the VBUCK voltage changes with line voltage. A good design
practice is to choose a desired nominal switching frequency
knowing that the switching frequency will decrease as the line
voltage drops and increase as the line voltage increases
(Figure 8).
For simplicity, choose efficiency between 75% and 85%.
CALCULATING OFF-TIME
The “Off-Time” of the LM3444 is set by the user and remains
fairly constant as long as the voltage of the LED stack remains
constant. Calculating the off-time is the first step in determining the switching frequency of the converter, which is integral
in determining some external component values.
PNP transistor Q3, resistor R4, and the LED string voltage
define a charging current into capacitor C11. A constant current into a capacitor creates a linear charging characteristic.
Resistor R4, capacitor C11 and the current through resistor
R4 (iCOLL), which is approximately equal to VLED/R4, are all
fixed. Therefore, dv is fixed and linear, and dt (tOFF) can now
be calculated.
Common equations for determining duty cycle and switching
frequency in any buck converter:
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FIGURE 8. Graphical Illustration of Switching Frequency
vs VBUCK
The off-time of the LM3444 can be programmed for switching
frequencies ranging from 30 kHz to over 1 MHz. A trade-off
between efficiency and solution size must be considered
when designing the LM3444 application.
The maximum switching frequency attainable is limited only
by the minimum on-time requirement (200 ns).
Therefore:
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During the off-time, the voltage seen by the inductor is approximately:
VL(OFF-TIME) = VLED
The value of VL(OFF-TIME) will be relatively constant, because
the LED stack voltage will remain constant. If we rewrite the
equation for an inductor inserting what we know about the
circuit during the off-time, we get:
The maximum voltage seen by the Buck Converter is:
INDUCTOR SELECTION
The controlled off-time architecture of the LM3444 regulates
the average current through the inductor (L2), and therefore
the LED string current. The input voltage to the buck converter
(VBUCK) changes with line variations and over the course of
each half-cycle of the input line voltage. The voltage across
the LED string is relatively constant, and therefore the current
through R4 is constant. This current sets the off-time of the
converter and therefore the output volt-second product
(VLED x off-time) remains constant. A constant volt-second
product makes it possible to keep the ripple through the inductor constant as the voltage at VBUCK varies.
Re-arranging this gives:
From this we can see that the ripple current (Δi) is proportional
to off-time (tOFF) multiplied by a voltage which is dominated
by VLED divided by a constant (L2).
These equations can be rearranged to calculate the desired
value for inductor L2.
Where:
Finally:
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Refer to “Design Example” section of the datasheet to better
understand the design process.
FIGURE 9. LM3444 External Components of the Buck
Converter
SETTING THE LED CURRENT
The LM3444 constant off-time control loop regulates the peak
inductor current (IL2). The average inductor current equals the
average LED current (I AVE). Therefore the average LED current is regulated by regulating the peak inductor current.
The equation for an ideal inductor is:
Given a fixed inductor value, L, this equation states that the
change in the inductor current over time is proportional to the
voltage applied across the inductor.
During the on-time, the voltage applied across the inductor is,
VL(ON-TIME) = VBUCK - (VLED + VDS(Q2) + IL2 x R3)
Since the voltage across the MOSFET switch (Q2) is relatively small, as is the voltage across sense resistor R3, we
can simplify this to approximately,
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LM3444
VL(ON-TIME) = VBUCK - VLED
Worst case scenario for minimum on time is when VBUCK is at
its maximum voltage (AC high line) and the LED string voltage
(VLED) is at its minimum value.
LM3444
The valley fill capacitors should be sized to supply energy to
the buck converter (VBUCK) when the input line is less than its
peak divided by the number of stages used in the valley fill
(tX). The capacitance value should be calculated for the maximum LED current.
30127525
FIGURE 10. Inductor Current Waveform in CCM
Knowing the desired average LED current, IAVE and the nominal inductor current ripple, ΔiL, the peak current for an application running in continuous conduction mode (CCM) is
defined as follows:
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FIGURE 11. Two Stage Valley-Ffill VBUCK Voltage
From the above illustration and the equation for current in a
capacitor, i = C x dV/dt, the amount of capacitance needed at
VBUCK will be calculated as follows:
At 60Hz, and a valley-fill circuit of two stages, the hold up time
(tX) required at VBUCK is calculated as follows. The total angle
of an AC half cycle is 180° and the total time of a half AC line
cycle is 8.33 ms. When the angle of the AC waveform is at
30° and 150°, the voltage of the AC line is exactly ½ of its
peak. With a two stage valley-fill circuit, this is the point where
the LED string switches from power being derived from AC
line to power being derived from the hold up capacitors (C7
and C9). 60° out of 180° of the cycle or 1/3 of the cycle the
power is derived from the hold up capacitors (1/3 x 8.33 ms
= 2.78 ms). This is equal to the hold up time (dt) from the
above equation, and dv is the amount of voltage the circuit is
allowed to droop. From the next section (“Determining Maximum Number of Series Connected LEDs Allowed”) we know
the minimum VBUCK voltage will be about 45V for a 90VAC to
135VAC line. At 90VAC low line operating condition input, ½ of
the peak voltage is 64V. Therefore with some margin the voltage at VBUCK can not droop more than about 15V (dv). (i) is
equal to (POUT/VBUCK), where POUT is equal to (VLED x ILED).
Total capacitance (C7 in parallel with C9) can now be calculated. See “ Design Example" section for further calculations
of the valley-fill capacitors.
Determining Maximum Number of Series Connected
LEDs Allowed:
The LM3444 is an off-line buck topology LED driver. A buck
converter topology requires that the input voltage (VBUCK) of
the output circuit must be greater than the voltage of the LED
stack (VLED) for proper regulation. One must determine what
the minimum voltage observed by the buck converter will be
before the maximum number of LEDs allowed can be determined. Two variables will have to be determined in order to
accomplish this.
1. AC line operating voltage. This is usually 90VAC to
135VAC for North America. Although the LM3444 can
operate at much lower and higher input voltages a range
is needed to illustrate the design process.
2. How many stages are implemented in the valley-fill circuit
(1, 2 or 3).
In this example the most common valley-fill circuit will be used
(two stages).
Or the LED current would then be,
This is important to calculate because this peak current multiplied by the sense resistor R3 will determine when the
internal comparator is tripped. The internal comparator turns
the control MOSFET off once the peak sensed voltage reaches 750 mV.
Current Limit: The trip voltage on the PWM comparator is
750 mV. However, if there is a short circuit or an excessive
load on the output, higher than normal switch currents will
cause a voltage above 1.27V on the ISNS pin which will trip
the I-LIM comparator. The I-LIM comparator will reset the RS
latch, turning off Q2. It will also inhibit the Start Pulse Generator and the COFF comparator by holding the COFF pin low.
A delay circuit will prevent the start of another cycle for 180
µs.
VALLEY FILL CAPACITORS
Determining voltage rating and capacitance value of the valley-fill capacitors:
The maximum voltage seen by the valley-fill capacitors is:
This is, of course, if the capacitors chosen have identical capacitance values and split the line voltage equally. Often a
20% difference in capacitance could be observed between
like capacitors. Therefore a voltage rating margin of 25% to
50% should be considered.
Determining the capacitance value of the valley-fill capacitors:
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SWITCHING MOSFET
The main switching MOSFET should be chosen with efficiency and robustness in mind. The maximum voltage across the
switching MOSFET will equal:
30127554
The average current rating should be greater than:
FIGURE 12. AC Line
IDS-MAX = ILED(-AVE)(DMAX)
Figure 12 shows the AC waveform. One can easily see that
the peak voltage (VPEAK) will always be:
RE-CIRCULATING DIODE
The LM3444 Buck converter requires a re-circulating diode
D10 (see the Typical Application circuit Figure 2) to carry the
inductor current during the MOSFET Q2 off-time. The most
efficient choice for D10 is a diode with a low forward drop and
near-zero reverse recovery time that can withstand a reverse
voltage of the maximum voltage seen at VBUCK. For a common
110VAC ± 20% line, the reverse voltage could be as high as
190V.
The voltage at VBUCK with a valley fill stage of two will look
similar to the waveforms of Figure 11.
The purpose of the valley fill circuit is to allow the buck converter to pull power directly off of the AC line when the line
voltage is greater than its peak voltage divided by two (two
stage valley fill circuit). During this time, the capacitors within
the valley fill circuit (C7 and C8) are charged up to the peak
of the AC line voltage. Once the line drops below its peak
divided by two, the two capacitors are placed in parallel and
deliver power to the buck converter. One can now see that if
the peak of the AC line voltage is lowered due to variations in
the line voltage the DC offset (VDC) will lower. VDC is the lowest value that voltage VBUCK will encounter.
The current rating must be at least:
ID = 1 - (DMIN) x ILED(AVE)
Or:
Design Example
Example:
Line voltage = 90VAC to 135VAC
Valley-Fill = two stage
The following design example illustrates the process of calculating external component values.
Known:
1. Input voltage range (90VAC – 135VAC)
2. Number of LEDs in series = 7
3. Forward voltage drop of a single LED = 3.6V
4. LED stack voltage = (7 x 3.6V) = 25.2V
Choose:
1. Nominal switching frequency, fSW-TARGET = 250 kHz
2. ILED(AVE) = 400 mA
3. Δi (usually 15% - 30% of ILED(AVE)) = (0.30 x 400 mA) =
120 mA
4. Valley fill stages (1,2, or 3) = 2
5. Assumed minimum efficiency = 80%
Calculate:
1. Calculate minimum voltage VBUCK equals:
Depending on what type and value of capacitors are used,
some derating should be used for voltage droop when the
capacitors are delivering power to the buck converter. With
this derating, the lowest voltage the buck converter will see is
about 42.5V in this example.
To determine how many LEDs can be driven, take the minimum voltage the buck converter will see (42.5V) and divide it
by the worst case forward voltage drop of a single LED.
Example: 42.5V/3.7V = 11.5 LEDs (11 LEDs with margin)
OUTPUT CAPACITOR
A capacitor placed in parallel with the LED or array of LEDs
can be used to reduce the LED current ripple while keeping
the same average current through both the inductor and the
LED array. With a buck topology the output inductance (L2)
can now be lowered, making the magnetics smaller and less
expensive. With a well designed converter, you can assume
2.
13
Calculate maximum voltage VBUCK equals:
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LM3444
that all of the ripple will be seen by the capacitor, and not the
LEDs. One must ensure that the capacitor you choose can
handle the RMS current of the inductor. Refer to
manufacture’s datasheets to ensure compliance. Usually an
X5R or X7R capacitor between 1 µF and 10 µF of the proper
voltage rating will be sufficient.
LM3444
3.
8.
9.
Calculate tOFF at VBUCK nominal line voltage:
Calculate C11:
10. Use standard value of 120 pF
11. Calculate ripple current: 400 mA X 0.30 = 120 mA
12. Calculate inductor value at tOFF = 3 µs:
4.
5.
6.
7.
Calculate tON(MIN) at high line to ensure that
tON(MIN) > 200 ns:
13. Choose C10: 1.0 µF 200V
14. Calculate valley-fill capacitor values: VAC low line =
90VAC, VBUCK minimum equals 60V. Set droop for 20V
maximum at full load and low line.
Calculate C11 and R4:
Choose current through R4: (between 50 µA and 100 µA)
70 µA
i) equals POUT/VBUCK (270 mA), dV equals 20V, dt equals
2.77 ms, and then CTOTAL equals 37 µF. Therefore C7 =
C9 = 22 µF
Use a standard value of 365 kΩ
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30127569
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LM3444
LM3444 Design Example 1
Input = 90VAC to 135VAC, VLED = 7 x HB LED String Application @ 400 mA
LM3444
Bill of Materials
Qty
Ref Des
Description
Mfr
Mfr PN
1
U1
IC, CTRLR, DRVR-LED, MSOP10
NSC
LM3444MM
1
BR1
Bridge Rectifiier, SMT, 400V, 800 mA
DiodesInc
HD04-T
1
L1
Common mode filter DIP4NS, 900 mA, 700
µH
Panasonic
ELF-11090E
1
L2
Inductor, SHLD, SMT, 1A, 470 µH
Coilcraft
MSS1260-474-KLB
2
L3, L4
Diff mode inductor, 500 mA 1 mH
Coilcraft
MSS1260-105KL-KLB
1
L5
Bead Inductor, 160Ω, 6A
Steward
HI1206T161R-10
3
C1, C2, C15
Cap, Film, X2Y2, 12.5MM, 250VAC, 20%, 10
nF
Panasonic
ECQ-U2A103ML
1
C4
Cap, X7R, 0603, 16V, 10%, 100 nF
MuRata
GRM188R71C104KA01D
2
C5, C6
Cap, X5R, 1210, 25V, 10%, 22 µF
MuRata
GRM32ER61E226KE15L
2
C7, C9
Cap, AL, 200V, 105C, 20%, 33 µF
UCC
EKXG201ELL330MK20S
1
C10
Cap, Film, 250V, 5%, 10 nF
Epcos
B32521C3103J
1
C12
Cap, X7R, 1206, 50V, 10%, 1.0 uF
Kemet
C1206F105K5RACTU
1
C11
Cap, C0G, 0603, 100V, 5%, 120 pF
MuRata
GRM1885C2A121JA01D
1
D1
Diode, ZNR, SOT23, 15V, 5%
OnSemi
BZX84C15LT1G
2
D2, D13
Diode, SCH, SOD123, 40V, 120 mA
NXP
BAS40H
4
D3, D4, D8, D9
Diode, FR, SOD123, 200V, 1A
Rohm
RF071M2S
1
D10
Diode, FR, SMB, 400V, 1A
OnSemi
MURS140T3G
1
D12
TVS, VBR = 144V
Fairchild
SMBJ130CA
1
R2
Resistor, 1206, 1%, 100 kΩ
Panasonic
ERJ-8ENF1003V
1
R3
Resistor, 1210, 5%, 1.8Ω
Panasonic
ERJ-14RQJ1R8U
1
R4
Resistor, 0603, 1%, 576 kΩ
Panasonic
ERJ-3EKF5763V
2
R6, R7
Resistor, 0805, 1%, 1.00 MΩ
Rohm
MCR10EZHF1004
2
R8, R10
Resistor, 1206, 0.0Ω
Yageo
RC1206JR-070RL
1
R9
Resistor, 1812, 0.0Ω
1
RT1
Thermistor, 120V, 1.1A, 50Ω @ 25°C
Thermometrics
CL-140
2
Q1, Q2
XSTR, NFET, DPAK, 300V, 4A
Fairchild
FQD7N30TF
1
Q3
XSTR, PNP, SOT23, 300V, 500 mA
Fairchild
MMBTA92
1
J1
Terminal Block 2 pos
Phoenix Contact
1715721
1
F1
Fuse, 125V, 1,25A
bel
SSQ 1.25
www.ti.com
16
LM3444
Physical Dimensions inches (millimeters) unless otherwise noted
MSOP-10 Pin Package (MM)
For Ordering, Refer to Ordering Information Table
NS Package Number MUB10A
SOIC-8 Pin Package (M)
For Ordering, Refer to Ordering Information Table
NS Package Number M08A
17
www.ti.com
LM3444 AC-DC Offline LED Driver
Notes
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Copyright © 2011, Texas Instruments Incorporated
LM3444
Application Note 2097 LM3444 - 230VAC, 8W Isolated Flyback LED Driver
Literature Number: SNVA462E
National Semiconductor
Application Note 2097
Clinton Jensen
May 3, 2011
Introduction
Key Features
This demonstration board highlights the performance of a
LM3444 based Flyback LED driver solution that can be used
to power a single LED string consisting of 4 to 10 series connected LEDs from an 180 VRMS to 265 VRMS, 50 Hz input
power supply. The key performance characteristics under
typical operating conditions are summarized in this application note.
This is a four-layer board using the bottom and top layer for
component placement. The demonstration board can be
modified to adjust the LED forward current, the number of series connected LEDs that are driven and the switching frequency. Refer to the LM3444 datasheet for detailed instructions.
A bill of materials is included that describes the parts used on
this demonstration board. A schematic and layout have also
been included along with measured performance characteristics.
•
•
•
Line injection circuitry enables PFC values greater than
0.98
Adjustable LED current and switching frequency
Flicker free operation
Applications
•
•
•
Solid State Lighting
Industrial and Commercial Lighting
Residential Lighting
Performance Specifications
Based on an LED Vf = 3.6V
Symbol
Parameter
Min
Typ
Max
VIN
Input voltage
180 VRMS
230 VRMS
265 VRMS
VOUT
LED string voltage
13 V
21.5 V
36 V
ILED
LED string average current
-
350 mA
-
POUT
Output power
-
7.5 W
-
fsw
Switching frequency
-
67 kHz
-
LM3444 - 230VAC, 8W Isolated Flyback LED Driver
LM3444 - 230VAC, 8W
Isolated Flyback LED Driver
Demo Board
AN-2097
30139704
© 2011 National Semiconductor Corporation
301397
www.national.com
AN-2097
LM3444 230VAC, 8W Isolated Flyback LED Driver Demo Board Schematic
+工
R3 ~ R2
R8~
R7
D5
SGND
vcc
R19
Ll NE
NEUTRAL
RT1
L1
F1
INPUT EMI FILTER AND RECTIFIER
30139701
Warning: The LM3444 evaluation board has exposed high voltage components that present a shock hazard. Caution must be taken when handling the evaluation
board. Avoid touching the evaluation board and removing any cables while the evaluation board is operating.
Warning: The ground connection on the evaluation board is NOT referenced to earth ground. If an oscilloscope ground lead is connected to the evaluation
board ground test point for analysis and the mains AC power is applied (without any isolation), the fuse (F1) will fail open. For bench evaluation, either
the input AC power source or the bench measurement equipment should be isolated from the earth ground connection. Isolating the evaliation board
(using 1:1 line isolation transformer) rather than the oscilloscope is highly recommended.
Warning: The LM3444 evaluation board should not be powered with an open load. For proper operation, ensure that the desired number of LEDs are connected
at the output before applying power to the evaluation board.
www.national.com
2
AN-2097
LM3444 Device Pin-Out
30139702
Pin Descriptions – 10 Pin MSOP
Pin #
Name
Description
1
NC
No internal connection.
2
NC
No internal connection.
3
NC
No internal connection.
4
COFF
5
FILTER
6
GND
Circuit ground connection.
7
ISNS
LED current sense pin. Connect a resistor from main switching MOSFET source, ISNS to GND to set the maximum
LED current.
8
GATE
Power MOSFET driver pin. This output provides the gate drive for the power switching MOSFET of the buck
controller.
9
VCC
Input voltage pin. This pin provides the power for the internal control circuitry and gate driver.
10
NC
No internal connection.
OFF time setting pin. A user set current and capacitor connected from the output to this pin sets the constant OFF
time of the switching controller.
Filter input. A capacitor tied to this pin filters the error amplifier. Could also be used as an analog dimming input.
3
www.national.com
AN-2097
Bill of Materials
Designator
Description
Manufacturer
Part Number
RoHS
U1
Offline LED Driver, PowerWise
National
Semiconductor
LM3444MM
Y
C1
Ceramic, X7R, 250VAC, 10%
Murata Electronics
North America
DE1E3KX332MA5BA01
Y
C2
Ceramic, Polypropylene, 400VDC, 10%
WIMA
MKP10-.033/400/5P10
Y
C3
CAP, CERM, 330pF, 630V, +/-5%, C0G/NP0, 1206
TDK
C3216C0G2J331J
Y
C4
Ceramic, X7R, 250V, X2, 10%, 2220
Murata Electronics
North America
GA355DR7GF472KW01L
Y
C5
CAP, Film, 0.033µF, 630V, +/-10%, TH
EPCOS Inc
B32921C3333K
Y
CAP, CERM, 1µF, 50V, +/-10%, X7R, 1210
MuRata
GRM32RR71H105KA01L
Y
C10
CAP, CERM, 0.47µF, 50V, +/-10%, X7R, 0805
MuRata
GRM21BR71H474KA88L
Y
C12
Aluminium Electrolytic, 680uF, 35V, 20%,
Nichicon
UHE1V681MHD6
Y
C13
CAP, CERM, 1µF, 35V, +/-10%, X7R, 0805
Taiyo Yuden
GMK212B7105KG-T
Y
C14
CAP, CERM, 0.1µF, 25V, +/-10%, X7R, 0603
MuRata
GRM188R71E104KA01D
Y
C15
CAP, TANT, 47uF, 16V, +/-10%, 0.35 ohm, 6032-28
SMD
AVX
TPSC476K016R0350
Y
C18
CAP, CERM, 2200pF, 50V, +/-10%, X7R, 0603
MuRata
GRM188R71H222KA01D
Y
C20
CAP, CERM, 330pF, 50V, +/-5%, C0G/NP0, 0603
MuRata
GRM1885C1H331JA01D
Y
D1
DIODE TVS 250V 600W UNI 5% SMD
Littelfuse
P6SMB250A
Y
D2
Diode, Switching-Bridge, 600V, 0.8A, MiniDIP
Diodes Inc.
HD06-T
Y
D3
Diode, Silicon, 1000V, 1A, SOD-123
Comchip Technology CGRM4007-G
Y
D4
Diode, Schottky, 100V, 1A, SMA
STMicroelectronics
STPS1H100A
Y
Diode, Zener, 13V, 200mW, SOD-323
Diodes Inc
DDZ13BS-7
Y
Diode, Zener, 36V, 550mW, SMB
ON Semiconductor
1SMB5938BT3G
Y
Diode, Schottky, 100V, 150 mA, SOD-323
STMicroelectronics
BAT46JFILM
Y
Fuse, 500mA, 250V, Time-Lag, SMT
Littelfuse Inc
0443.500DR
Y
H1, H2, H5, H6 Standoff, Hex, 0.5"L #4-40 Nylon
Keystone
1902C
Y
H3, H4, H7, H8 Machine Screw, Round, #4-40 x 1/4, Nylon, Philips
panhead
B&F Fastener Supply NY PMS 440 0025 PH
Y
C9, C11
D5, D10
D6
D7, D8, D9
F1
J1, J2
Conn Term Block, 2POS, 5.08mm PCB
Phoenix Contact
1715721
Y
L1, L2
Inductor, Radial Lead Inductors, Shielded, 4.7mH,
130mA, 12.20ohm, 7.5mm Radial,
TDK Corporation
TSL080RA-472JR13-PF
Y
Terminal, 22 Gauge Wire, Terminal, 22 Guage Wire
3M
923345-02-C
Y
Q1
MOSFET, N-CH, 600V, 200mA, SOT-223
Fairchild
Semiconductor
FQT1N60CTF_WS
Y
Q2
Transistor, NPN, 300V, 500mA, SOT-23
Diodes Inc.
MMBTA42-7-F
Y
Q3
MOSFET, N-CH, 650V, 800mA, IPAK
Infineon
Technologies
SPU01N60C3
Y
R1
RES, 221 ohm, 1%, 0.25W, 1206
Vishay-Dale
CRCW1206221RFKEA
Y
R2, R7
RES, 200k ohm, 1%, 0.25W, 1206
Vishay-Dale
CRCW1206200KFKEA
Y
R3, R8
RES, 309k ohm, 1%, 0.25W, 1206
Vishay-Dale
CRCW1206309KFKEA
Y
R4, R12
RES, 10k ohm, 5%, 0.25W, 1206
Vishay-Dale
CRCW120610K0JNEA
Y
R13
RES, 33.0 ohm, 1%, 0.25W, 1206
Vishay-Dale
CRCW120633R0FKEA
Y
R14
RES, 10 ohm, 5%, 0.125W, 0805
Vishay-Dale
CRCW080510R0JNEA
Y
R15
RES, 10.0k ohm, 1%, 0.1W, 0603
Vishay-Dale
CRCW060310K0FKEA
Y
R19
RES, 10 ohm, 5%, 0.1W, 0603
Vishay-Dale
CRCW060310R0JNEA
Y
R20
RES, 1.91k ohm, 1%, 0.1W, 0603
Vishay-Dale
CRCW06031K91FKEA
Y
R21
RES, 2.70 ohm, 1%, 0.25W, 1206
Panasonic
ERJ-8RQF2R7V
Y
LED+, LED-,
TP7, TP8
www.national.com
4
Description
Manufacturer
Part Number
RoHS
R22
RES, 10.7 ohm, 1%, 0.125W, 0805
Vishay-Dale
CRCW080510R7FKEA
Y
R23
RES, 324k ohm, 1%, 0.1W, 0603
Vishay-Dale
CRCW0603324KFKEA
Y
RT1
Current Limitor Inrush, 60Ohm, 20%, 5mm Raidal
Cantherm
MF72-060D5
Y
T1
FLBK TFR, 2.07 mH, Np=140T, Ns=26T, Na= 20T
Wurth Elektornik
750815040 REV 1
Y
Terminal, Turret, TH, Double
Keystone Electronics 1502-2
Y
Varistor 275V 55J 10mm DISC
EPCOS Inc
Y
TP9, TP10
VR1
5
S10K275E2
www.national.com
AN-2097
Designator
AN-2097
Transformer Design
Mfg: Wurth Electronics, Part #: 750815040 Rev. 01
30139709
Parameter
Test Conditions
Value
D.C. Resistance (3-1)
20°C
1.91 Ω ± 10%
D.C. Resistance (6-4)
20°C
0.36 Ω ± 10%
D.C. Resistance (10-13)
20°C
Inductance (3-1)
10 kHz, 100 mVAC
0.12 Ω ± 10%
2.12 mH ± 10%
Inductance (6-4)
10 kHz, 100 mVAC
46.50 µH ± 10%
Inductance (10-13)
10 kHz, 100 mVAC
74.00 µH ± 10%
Leakage Inductance (3-1)
100 kHz, 100 mAVAC (tie 6+4, 10+13)
18.0 µH Typ., 22.60 µH Max.
Dielectric (1-13)
tie (3+4), 4500 VAC, 1 second
4500 VAC, 1 minute
www.national.com
Turns Ratio
(3-1):(6-4)
7:1 ± 1%
Turns Ratio
(3-1):(10:13)
5.384:1 ± 1%
6
AN-2097
Demo Board Wiring Overview
30139703
Wiring Connection Diagram
Test Point
Name
I/O
Description
TP10, J2-1
LED +
Output
LED Constant Current Supply
Supplies voltage and constant-current to anode of LED string.
TP9, J2-2
LED -
Output
LED Return Connection (not GND)
Connects to cathode of LED string. Do NOT connect to GND.
J1-1
LINE
Input
AC Line Voltage
Connects directly to AC line of a 230VAC system.
J1-2
NEUTRAL
Input
AC Neutral
Connects directly to AC neutral of a 230VAC system.
Demo Board Assembly
30139705
Top View
30139706
Bottom View
7
www.national.com
(Note 1, Note 2, Note 3)
Efficiency vs. Line Voltage
Original Circuit
Efficiency vs. Line Voltage
Modified Circuits
0.97
10 LEDs
0.93
8 LEDs
EFFICIENCY
EFFICIENCY
0.87
0.85
6 LEDs
0.82
0.89
Mod C (10 LEDs)
Mod B (8 LEDs)
0.85
0.81
0.77
0.73
4 LEDs
0.80
Original (6 LEDs)
Mod A (4 LEDs)
0.68
0.64
0.78
180 190 200 210 220 230 240 250 260
0.60
180 190 200 210 220 230 240 250 260
INPUT VOLTAGE (VRMS)
INPUT VOLTAGE (VRMS)
30139710
30139714
LED Current vs. Line Voltage
Original Circuit
LED Current vs. Line Voltage
Modified Circuits
600
650
LED CURRENT (mA)
450
550
4 LEDs
550
LED CURRENT (mA)
AN-2097
Typical Performance Characteristics
6 LEDs
350
250
8 LEDs
150
450
Mod B (8 LEDs)
400
350
300
250
200
150
10 LEDs
Original (6 LEDs)
Mod A (4 LEDs)
100
180 190 200 210 220 230 240 250 260
50
180 190 200 210 220 230 240 250 260
INPUT VOLTAGE (VRMS)
INPUT VOLTAGE (VRMS)
30139711
www.national.com
500
Mod C (10 LEDs)
30139715
8
AN-2097
Power Factor vs. Line Voltage
Output Power vs. Line Voltage
Original Circuit
1.000
12
0.995
11
0.990
POWER FACTOR
OUTPUT POWER (W)
0.985
0.980
0.975
0.970
0.965
0.960
10
9
8
10 LEDs
8 LEDs
4 LEDs
7
6 LEDs
6
5
4
0.955
3
0.950
180 190 200 210 220 230 240 250 260
2
180 190 200 210 220 230 240 250 260
LINE VOLTAGE (VRMS)
INPUT VOLTAGE (VRMS)
30139713
30139712
Output Power vs. Line Voltage
Modified Circuits
Line Voltage and Line Current
(VIN = 230VRMS, 6 LEDs, ILED = 350mA)
25.0
OUTPUT POWER (W)
22.5
20.0
Mod B (8 LEDs)
17.5
15.0
Mod C (10 LEDs)
12.5
10.0
7.5
5.0
2.5
Mod A (4 LEDs)
Original (6 LEDs)
0.0
180 190 200 210 220 230 240 250 260
30139718
Ch1: Line Voltage (100 V/div); Ch3: Line Current
(20 mA/div); Time (4 ms/div)
INPUT VOLTAGE (VRMS)
30139717
Output Voltage and LED Current
(VIN = 230VRMS, 6 LEDs, ILED = 350mA)
Power MOSFET Drain and ISNS (Pin-7) Voltage
(VIN = 230VRMS, 6 LEDs, ILED = 350mA)
30139720
30139721
Ch1: Output Voltage (10 V/div); Ch3: LED Current
(100 mA/div); Time (4 ms/div)
Ch1: Drain Voltage (100V/div); Ch4: ISNS Voltage
(500 mV/div); Time (4 µs/div)
9
www.national.com
AN-2097
FILTER (Pin-5) and ISNS (Pin-7) Voltage
(VIN=230VRMS, 6 LEDs, ILED = 350mA
30139722
Ch1: FILTER Voltage (200 mV/div); ISNS Voltage
(200 mV/div); Time (4 µs/div)
Note 1: Original Circuit (6 LEDs operating at 350mA): R21 = 2.7Ω; Modification A (10 LEDs operating at 375mA): R21 = 1.8Ω; Modification B (8 LEDs operating
at 350mA): R21 = 2.2Ω; Modification C (4 LEDs operating at 315mA): R21 = 3.9Ω
Note 2: The output power can be varied to achieve desired LED current by interpolating R21 values between the maximum of 3.9 Ω and minimum of 1.8 Ω
Note 3: The maximum output voltage is clamped to 36 V. For operating LED string voltage > 36 V, replace D6 with suitable alternative
PCB Layout
30139707
Top Layer
www.national.com
10
AN-2097
30139740
Top Middle Layer
30139741
Bottom Middle Layer
11
www.national.com
AN-2097
30139708
Bottom Layer
www.national.com
12
The LED driver is designed to accurately emulate an incandescent light bulb and therefore behave as an emulated
resistor. The resistor value is determined based on the LED
string configuration and the desired output power. The circuit
then operates in open-loop, with a fixed duty cycle based on
a constant on-time and constant off-time that is set by selecting appropriate circuit components.
PERFORMANCE
In steady state, the LED string voltage is measured to be
21.55 V and the average LED current is measured as 347.5
MEASURED EFFICIENCY AND LINE REGULATION (6 LEDS)
VIN (VRMS)
IIN (mARMS)
PIN(W)
VOUT (V)
ILED (mA)
POUT (W)
Efficiency (%) Power Factor
180
30.65
5.42
20.59
219.40
4.52
83.3
0.9867
190
32.35
6.06
20.80
242.55
5.05
83.3
0.9869
200
34.21
6.75
21.00
267.37
5.62
83.2
0.9870
210
36.01
7.47
21.18
293.39
6.21
83.2
0.9871
220
37.74
8.20
21.37
320.18
6.84
83.3
0.9872
230
39.44
8.96
21.55
347.51
7.49
83.6
0.9873
240
41.22
9.76
21.72
375.52
8.15
83.6
0.9874
250
43..29
10.62
21.90
404.82
8.86
83.5
0.9875
260
45.06
11.57
22.07
436.75
9.64
83.3
0.9877
the fundamental current (as shown in the following table) and
therefore meets the requirements of the IEC 61000-3-2
Class-3 standard. Total harmonic distortion was measured to
be less than 1.2%.
CURRENT THD
The LED driver is able to achieve close to unity power factor
(PF ~ 0.98) which meets Energy Star requirements. This design also exhibits low current harmonics as a percentage of
MEASURED HARMONIC CURRENT
Harmonic
Class C Limit (mA)
Measured (mA)
2
0.78
0.022
3
11.61
0.125
5
3.90
0.11
7
2.73
0.105
9
1.95
0.11
11
1.73
0.15
13
1.73
0.093
15
1.73
0.071
17
1.73
0.154
19
1.73
0.165
21
1.73
0.065
23
1.73
0.065
25
1.73
0.08
27
1.73
0.084
29
1.73
0.065
31
1.73
0.07
13
www.national.com
AN-2097
mA. The 100 Hz current ripple flowing through the LED string
was measured to be 194 mApk-pk at full load. The magnitude
of the ripple is a function of the value of energy storage capacitors connected across the output. The ripple current can
be reduced by increasing the value of energy storage capacitor or by increasing the LED string voltage.
The LED driver switching frequency is measured to be close
to the specified 67 kHz. The circuit operates with a constant
duty cycle of 0.21 and consumes near 9W of input power. The
driver steady state performance for an LED string consisting
of 6 series LEDs is summarized in the following table.
Experimental Results
AN-2097
Electromagnetic Interference (EMI)
The EMI input filter of this evaluation board is configured as
shown in the following circuit diagram.
30139731
FIGURE 1. Input EMI Filter and Rectifier Circuit
In order to get a quick estimate of the EMI filter performance,
only the PEAK conductive EMI scan was measured and the
data was compared to the Class B conducted EMI limits published in FCC – 47, section 15.(Note 4)
30139732
FIGURE 2. Peak Conductive EMI scan per CISPR-22, Class B Limits
Note 4: CISPR 15 compliance pending
www.national.com
14
AN-2097
ILED = 348 mA
# of LEDs = 6
POUT = 7.2 W
The results are shown in the following figures.
Thermal Analysis
The board temperature was measured using an IR camera
(HIS-3000, Wahl) while running under the following conditions:
VIN = 230 VRMS
30139733
FIGURE 3. Top Side Thermal Scan
30139734
FIGURE 4. Bottom Side Thermal Scan
15
www.national.com
AN-2097
TER pin, the on-time can be made to be constant. With a DCM
Flyback, Δi needs to increase as the input voltage line increases. Therefore a constant on-time (since inductor L is
constant) can be obtained.
By using the line voltage injection technique, the FILTER pin
has the voltage wave shape shown in Figure 6 on it. Voltage
at VFILTER peak should be kept below 1.25V. At 1.25V current
limit is tripped. C11 is small enough not to distort the AC signal
but adds a little filtering.
Although the on-time is probably never truly constant, it can
be observed in Figure 7 how (by adding the rectified voltage)
the on-time is adjusted.
Circuit Analysis and Explanations
INJECTING LINE VOLTAGE INTO FILTER (ACHIEVING
PFC > 0.98)
If a small portion (750mV to 1.00V) of line voltage is injected
at FILTER of the LM3444, the circuit is essentially turned into
a constant power flyback as shown in Figure 5.
30139737
FIGURE 6. FILTER Waveform
For this evaluation board, the following resistor values are
used:
R3 = R8 = 309 kΩ
R20 = 1.91 kΩ
Therefore the voltages observed on the FILTER pin will be as
follows for listed input voltages:
For VIN = 180VRMS, VFILTER, Pk = 0.78V
For VIN = 230VRMS, VFILTER, Pk = 1.00V
For VIN = 265VRMS, VFILTER, Pk = 1.15V
Using this technique, a power factor greater than 0.98 can be
achieved without additional passive active power factor control (PFC) circuitry.
30139735
FIGURE 5. Line Voltage Injection Circuit
The LM3444 works as a constant off-time controller normally,
but by injecting the 1.0VPk rectified AC voltage into the FIL-
30139736
FIGURE 7. Typical Operation of FILTER Pin
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16
AN-2097
Notes
17
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LM3444 - 230VAC, 8W Isolated Flyback LED Driver
Notes
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AN-2097
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LM3444
Application Note 2083 LM3444 A19 Edison Retrofit Evaluation Board
Literature Number: SNVA455B
National Semiconductor
Application Note 2083
Clinton Jensen
December 2, 2010
Introduction
input voltage are valid only for the demonstration board as
shipped with the schematic below. Please refer to the LM3444
data sheet for detailed information regarding the LM3444 device. The board is currently set up to drive five to thirteen
series connected LEDs, but the evaluation board may be
modified to accept more series LEDs. Refer to the tables in
this document for modifying the board to accept more LEDs
and/or adjust for different current levels.
The evaluation board included in this shipment converts
85VAC to 135VAC input and drives five to thirteen series connected LED’s at the currents listed in the Evaluation Board
Operating Conditions section. This is a two-layer board using
the bottom and top layer for component placement. The board
is surrounded by a larger area allowing for extra test points
and connectors for ease of evaluation. The actual board size
is contained inside the larger outer area and can be cut out
for the smallest size possible. The evaluation board can be
modified to adjust the LED forward current and the number of
series connected LEDs. The topology used for this evaluation
board eliminates the need for passive power factor correction
and results in high efficiency and power factor with minimal
component count which results in a size that can fit in a standard A19 Edison socket. Output current is regulated within
±15% of nominal from circuit to circuit and over line voltage
variation. Refer to the LM3444 datasheet for details on the
LM3444 IC.
A bill of materials below describes the parts used on this
demonstration board. A schematic and layout have also been
included below along with measured performance characteristics including EMI/EMC data. The above restrictions for the
Evalution Board Operating
Conditions
VIN = 85VAC to 135VAC
5 to 13 series connected LEDs as configured with the currents
listed below
Can drive up to 18 series LEDs (see table)
ILED = 340 mA (5 LEDs)
ILED = 300 mA (7 LEDs)
ILED = 260 mA (9 LEDs)
ILED = 230 mA (11 LEDs)
ILED = 205 mA (13 LEDs)
LM3444 A19 Edison Retrofit Evaluation Board
LM3444 A19 Edison Retrofit
Evaluation Board
Simplified LM3444 Schematic
30131201
Warning: This LM3444 evaluation PCB is a non-isolated design. The ground connection on the evaluation board is NOT referenced to earth ground. If an
oscilloscope ground lead is connected to the evaluation board ground test point for analysis, and AC power is applied, the fuse (F1) will fail open.
The oscilloscope should be powered via an isolation transformer before an oscilloscope ground lead is connected to the evaluation board.
© 2010 National Semiconductor Corporation
301312
www.national.com
AN-2083
Warning: The LM3444 evaluation boards have no isolation or any type of protection from shock. Caution must be taken when handling evaluation board.
Avoid touching evaluation board, and removing any cables while evaluation board is operating. Isolating the evaluation board rather than the
oscilloscope is highly recommended.
AN-2083
Pin-Out
30131203
10-Pin MSOP
Pin Description 10 Pin MSOP
Pin #
Name
1
NC
Description
No internal connection.
2
NC
No internal connection.
3
NC
No internal connection.
4
COFF
5
FILTER
OFF time setting pin. A user set current and capacitor connected from the output to this pin sets the constant
OFF time of the switching controller.
Filter input. A capacitor tied to this pin filters the error amplifier. Could also be used as an analog dimming
input.
6
GND
Circuit ground connection.
7
ISNS
LED current sense pin. Connect a resistor from main switching MOSFET source, ISNS to GND to set the
maximum LED current.
8
GATE
Power MOSFET driver pin. This output provides the gate drive for the power switching MOSFET of the buck
controller.
9
VCC
Input voltage pin. This pin provides the power for the internal control circuitry and gate driver.
10
NC
No internal connection.
www.national.com
2
跚跚
跚跚 m
m
R2
13盖
mm
盯
10
11-1318301-2
07
'"
15V
MMSZ5245B _
织)1).123
GNO
l借
口 10
GNO
LM3444 Evaluation Board Schematic
01
3
30131207
www.national.com
AN-2083
AN-2083
Bill of Materials LM3444 Evaluation Board
REF DES
Description
MFG
U1
IC DRIVER LED 10MSOP
National Semiconductor
MFG Part Number
LM3444MM
C1, C10
Ceramic, 47000pF, 500V, X7R, 1210
Johanson Dielectrics
501S41W473KV4E
C2
CAP FILM MKP .0047µF 310VAC X2
Vishay/BC Components
BFC233820472
C3
CAP 470µF 50V ELECT PW RADIAL
Nichicon
UPW1H471MHD
TDK Corporation
C4532X7R2E334K
C4/RBLDR (Note 1)
DNP
C5
Ceramic, .33µF, 250V, X7R, 1812
C6
CAP .10µF 305VAC EMI SUPPRESSION
EPCOS
B32921C3104M
C8
Ceramic, 47µF, X5R, 16V, 1210
MuRata
GRM32ER61C476ME15L
C12
Ceramic, 470pF, 50V, X7R, 0603
MuRata
GRM188R71H471KA01D
C15
Ceramic, 0.1µF, 16V, X7R, 0603
MuRata
GRM188R71C104KA01D
C14
Ceramic, 0.47µF, 16V, X7R, 0603
MuRata
GRM188R71C474KA88D
D1
DIODE SCHOTTKY 1A 200V PWRDI 123
Diodes Inc.
DFLS1200-7
D2
Bridge Rectifier, Vr = 400V, Io = 0.8A, Vf = 1V
Diodes Inc.
HD04-T
D4
DIODE FAST 1A 300V SMA
Fairchild Semi conductor
ES1F
D7
DIODE ZENER 15V 500MW SOD-123
Fairchild Semi conductor
MMSZ5245B
D8
DIODE SCHOTTKY 1A 200V PWRDI 123
Diodes Inc.
DFLS1200-7
F1
FUSE 1A 125V FAST
Cooper/Bussman
6125FA1A
J5, J10
CONN HEADER .312 VERT 2POS TIN
Tyco Electronics
1-1318301-2
L1, L2
INDUCTOR 3900µH .12A RADIAL
J.W. Miller/Bourns
RL875S-392K-RC
L3
820µH, Shielded Drum Core
Coilcraft Inc.
MSS1038-824KL
M1
JUMPER WIRE 0.3" J6 TO J1
3M
923345-03-C
M2
JUMPER WIRE 0.3" J7 to J4
3M
923345-03-C
M3
JUMPER WIRE 0.3" J2 TO J8
3M
923345-03-C
M4
JUMPER WIRE 0.3" J3 TO J9
3M
923345-03-C
Q1
MOSFET N-CH 240V 260MA SOT-89
Infineon Technologies
BSS87 L6327
Q2
MOSFET N-CH 250V 4.4A DPAK
Fairchild Semi conductor
FDD6N25TM
R1, R3
RES 200kΩ, 0.25W, 1%, 1206
Vishay-Dale
CRCW1206200kFKEA
R2, R7
RES 274kΩ, 0.25W, 1%, 1206
Vishay-Dale
CRCW1206274kFKEA
R4
RES 430Ω, 1/2W, 5%, 2010
Vishay-Dale
CRCW2010430RJNEF
R6, R24
RES 30.1kΩ, 0.25W, 1%, 1206
Vishay-Dale
CRCW120630k1FKEA
R10
DNP
R12
RES 4.7Ω, 0.1W, 5%, 0603
Vishay-Dale
CRCW06034R70JNEA
R14
RES 1.54Ω, 1/4W, 1%, 1206
Vishay-Dale
CRCW12083R54FNEA
R15
RES 3.16kΩ, 0.1w, 1%, 0603
Vishay-Dale
CRCW06033K16FKEA
R16
RES 255kΩ, 0.1W, 1%, 0603
Vishay-Dale
CRCW0603255KFKEA
R22
RES 40.2Ω, 0.125W, 1%, 0805
Vishay-Dale
CRCW080540R2FKEA
RT1
CURRENT LIMITOR INRUSH 60Ω 20%
Cantherm
MF72-060D5
TP1, TP2, TP3, TP4
Terminal, Turret, TH, Double
Keystone Electronics
1502-2
Note 1: C4/RBLDR is a dual purpose pad which is unpopulated by default. A ceramic capacitor (C4) may be used here if extra high frequency bypassing is desired
across the LED load. Alternatively a bleeder resistor (RBLDR) in the range of 10kΩ to 100kΩ may be placed here to quickly discharge C3 and prevent prolonged
LED glow due to the energy stored in C3.
www.national.com
4
# of LEDs
Output Current (mA)
Original Circuit
Output Current (mA)
Modification A (Note 2)
Output Current (mA)
Modification B (Note 3)
Output Current (mA)
Modification C (Note 4)
2
520
3
500
4
475
5
340
248
265
455
6
315
235
250
432
7
300
222
237
412
8
275
210
224
9
260
200
212
10
245
190
200
11
230
180
190
12
215
170
180
13
205
164
170
14 (Note 5)
196
156
162
15 (Note 5)
190
150
155
16 (Note 5)
183
142
148
17 (Note 5)
175
135
142
18 (Note 5)
170
130
137
Note 2: Modification A: R14 = 2.37Ω, R16 = 150kΩ, C3 = 330µF, 63V.
Note 3: Modification B: R14 = 2.2Ω, R16 = 165kΩ.
Note 4: Modification C: R14 = 1.2Ω, R16 = 137kΩ, L3 = 470µH, C3 = 1000µF, 25V.
Note 5: For all applications using greater than 13 LEDs a 330µF, 63V output capacitor (C3) was used.
5
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AN-2083
Output Current versus Number of LEDs for Various Modifications
AN-2083
Typical Performance Characteristics
Efficiency vs. Line Voltage
Original Circuit
Power Factor vs. Line Voltage
Original Circuit
30131202
30131204
Efficiency vs. Line Voltage
Modification A
Power Factor vs. Line Voltage
Modification A
30131211
30131212
Efficiency vs. Line Voltage
Modification B
Power Factor vs. Line Voltage
Modification B
30131213
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30131214
6
AN-2083
PCB Layout
30131210
Top Layer
30131209
Bottom Layer
Warning: The LM3444 evaluation boards have no isolation or any type of protection from shock. Caution must be taken when handling evaluation board. Avoid
touching evaluation board, and removing any cables while evaluation board is operating. Isolating the evaluation board rather than the oscilloscope
is highly recommended.
7
www.national.com
AN-2083
EMI/EMC Information
30131215
Radiated EMI
30131216
Conducted EMC. Line = Blue, Neutral = Black.
Frequency
Quasi-peak
Amplitude
Quasi-peak
Limit
Quasi-peak
Delta
Average
Amplitude
Average Limit
Neutral
154 kHz
57
66
-9
47
56
-9
Line
1.1 MHz
31
46
-15
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8
Average
Delta
AN-2083
Notes
9
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LM3444 A19 Edison Retrofit Evaluation Board
Notes
For more National Semiconductor product information and proven design tools, visit the following Web sites at:
www.national.com
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AN-2083
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LM3444
Application Note 2082 LM3444 -120VAC, 8W Isolated Flyback LED Driver
Literature Number: SNVA454D
National Semiconductor
Application Note 2082
Clinton Jensen
December 7, 2010
Introduction
Key Features
This demonstration board highlights the performance of a
LM3444 based Flyback LED driver solution that can be used
to power a single LED string consisting of 4 to 8 series connected LEDs from an 90 VRMS to 135 VRMS, 60 Hz input power
supply. The key performance characteristics under typical
operating conditions are summarized in this application note.
This is a two-layer board using the bottom and top layer for
component placement. The demonstration board can be
modified to adjust the LED forward current, the number of series connected LEDs that are driven and the switching frequency. Refer to the LM3444 datasheet for detailed instructions.
A bill of materials is included that describes the parts used on
this demonstration board. A schematic and layout have also
been included along with measured performance characteristics.
•
•
•
Line injection circuitry enables PFC values greater than
0.99
Adjustable LED current and switching frequency
Flicker free operation
Applications
•
•
•
Solid State Lighting
Industrial and Commercial Lighting
Residential Lighting
Performance Specifications
Based on an LED Vf = 3.57V
Symbol
Parameter
Min
Typ
Max
VIN
Input voltage
90 VRMS
120 VRMS
135 VRMS
VOUT
LED string voltage
12 V
21.4 V
30 V
ILED
LED string average current
-
350 mA
-
POUT
Output power
-
7.6 W
-
fsw
Switching frequency
-
79 kHz
-
LM3444 - 120VAC, 8W Isolated Flyback LED Driver
LM3444 -120VAC, 8W
Isolated Flyback LED Driver
Demo Board
30131168
AN-2082
© 2010 National Semiconductor Corporation
301311
www.national.com
AN-2082
LM3444 120VAC, 8W Isolated Flyback LED Driver Demo Board Schematic
30131101
Warning: The LM3444 evaluation board has exposed high voltage components that present a shock hazard. Caution must be taken when handling the evaluation
board. Avoid touching the evaluation board and removing any cables while the evaluation board is operating. Isolating the evaluation board rather
than the oscilloscope is highly recommended.
Warning: The ground connection on the evaluation board is NOT referenced to earth ground. If an oscilloscope ground lead is connected to the evaluation
board ground test point for analysis and AC power is applied, the fuse (F1) will fail open. The oscilloscope should be powered via an isolation
transformer before an oscilloscope ground lead is connected to the evaluation board.
Warning: The LM3444 evaluation board should not be powered with an open load. For proper operation, ensure that the desired number of LEDs are connected
at the output before applying power to the evaluation board.
www.national.com
2
AN-2082
LM3444 Device Pin-Out
30131102
Pin Description 10 Pin MSOP
Pin #
Name
Description
1
NC
No internal connection.
2
NC
No internal connection.
3
NC
No internal connection.
4
COFF
5
FILTER
6
GND
Circuit ground connection.
7
ISNS
LED current sense pin. Connect a resistor from main switching MOSFET source, ISNS to GND to set the maximum
LED current.
8
GATE
Power MOSFET driver pin. This output provides the gate drive for the power switching MOSFET of the buck
controller.
9
VCC
Input voltage pin. This pin provides the power for the internal control circuitry and gate driver.
10
NC
No internal connection.
OFF time setting pin. A user set current and capacitor connected from the output to this pin sets the constant OFF
time of the switching controller.
Filter input. A capacitor tied to this pin filters the error amplifier. Could also be used as an analog dimming input.
3
www.national.com
AN-2082
Bill of Materials
Designator
Description
Manufacturer
Part Number
AA1
Printed Circuit Board
-
551600530-001A
C1
CAP .047UF 630V METAL POLYPRO
EPCOS Inc
B32559C6473K000
C2
CAP 10000PF X7R 250VAC X2 2220
Murata Electronics North America
GA355DR7GB103KY02L
C3, C4
CAP 330UF 35V ELECT PW
Nichicon
UPW1V331MPD6
C6
CAP .10UF 305VAC EMI SUPPRESSION
EPCOS
B32921C3104M
C7
CAP, CERM, 0.1µF, 16V, +/-10%, X7R,
0805
Kemet
C0805C104K4RACTU
C8
CAP CER 47UF 16V X5R 1210
MuRata
GRM32ER61C476ME15L
C11
CAP CER 2200PF 50V 10% X7R 0603
MuRata
GRM188R71H222KA01D
C12
CAP CER 330PF 50V 5% C0G 0603
MuRata
GRM1885C1H331JA01D
C13
CAP CER 2200PF 250VAC X1Y1 RAD
TDK Corporation
CD12-E2GA222MYNS
D1
DIODE TVS 150V 600W UNI 5% SMB
Littlefuse
SMAJ120A
D2
RECT BRIDGE GP 600V 0.5A MINIDIP
Diodes Inc.
RH06-T
D3
DIODE RECT GP 1A 1000V MINI-SMA
Comchip Technology
CGRM4007-G
D4
DIODE SCHOTTKY 100V 1A SMA
ST Microelectronics
STPS1H100A
D5
DIODE ZENER 30V 1.5W SMA
ON Semiconductor
1SMA5936BT3G
D7
DIODE ZENER 12V 200MW
Fairchild Semiconductor
MM5Z12V
D8
DIODE SWITCH 200V 200MW
Diode Inc
BAV20WS-7-F
F1
FUSE BRICK 1A 125V FAST 6125FA
Cooper/Bussmann
6125FA
J1, J2, J3, J4, TP8,
TP9, TP10
16 GA WIRE HOLE, 18 GA WIRE HOLE
3M
923345-02-C
J5, J6
CONN HEADER .312 VERT 2POS TIN
Tyco Electronics
1-1318301-2
L1, L2
INDUCTOR 4700UH .13A RADIAL
TDK Corporation
TSL0808RA-472JR13-PF
Q1
MOSFET N-CH 600V 90MA SOT-89
Infineon Technologies
BSS225 L6327
Q2
MOSFET N-CH 600V 1.8A TO-251
Infineon Technology
SPU02N60S5
R1, R3
RES 200K OHM 1/4W 5% 1206 SMD
Vishay-Dale
CRCW1206200KJNEA
R2, R7
RES, 309k ohm, 1%, 0.25W, 1206
Vishay-Dale
CRCW1206309KFKEA
R6, R24
RES, 10.5k ohm, 1%, 0.125W, 0805
Vishay-Dale
CRCW080510K5FKEA
R12
RES 4.7 OHM 1/10W 5% 0603 SMD
Vishay-Dale
CRCW06034R70JNEA
R13
RES 10 OHM 1/8W 5% 0805 SMD
Vishay-Dale
CRCW080510R0JNEA
R14
RES 1.50 OHM 1/4W 1% 1206 SMD
Vishay-Dale
CRCW12061R50FNEA
R15
RES 3.48K OHM 1/10W 1% 0603 SMD
Vishay-Dale
CRCW06033K48FKEA
R16
RES 191K OHM 1/10W 1% 0603 SMD
Vishay-Dale
CRCW0603191KFKEA
CRCW080540R2FKEA
R22
RES 40.2 OHM 1/8W 1% 0805 SMD
Vishay-Dale
RT1
CURRENT LIMITOR INRUSH 60OHM 20%
Cantherm
MF72-060D5
T1
Transformer
Wurth Electronics
750311553 Rev. 01
TP2-TP5
Terminal, Turret, TH, Double
Keystone Electronics
1502-2
TP7
TEST POINT ICT
-
-
U1
Offline LED Driver, PowerWise
National Semiconductor
LM3444MM
www.national.com
4
AN-2082
Demo Board Wiring Overview
30131143
Wiring Connection Diagram
Test Point
Name
I/O
Description
TP3
LED +
Output
LED Constant Current Supply
Supplies voltage and constant-current to anode of LED string.
TP2
LED -
Output
LED Return Connection (not GND)
Connects to cathode of LED string. Do NOT connect to GND.
TP5
LINE
Input
AC Line Voltage
Connects directly to AC line of a 120VAC system.
TP4
NEUTRAL
Input
AC Neutral
Connects directly to AC neutral of a 120VAC system.
Demo Board Assembly
30131169
Top View
30131170
Bottom View
5
www.national.com
(Note 1)
Efficiency vs. Line Voltage
Original Circuit
Efficiency vs. Line Voltage
Modified Circuits
86
86
84
8 LEDs
EFFICIENCY (%)
EFFICIENCY (%)
84
82
6 LEDs
80
4 LEDs
78
76
80
90
100
110
120
130
Original
Mod A
82
80
Mod B
Mod C
78
76
140
80
LINE VOLTAGE (VRMS)
90
100
110
120
130
140
LINE VOLTAGE (VRMS)
30131187
30131188
LED Current vs. Line Voltage
Original Circuit
LED Current vs. Line Voltage
Modified Circuits
1.0
1.0
0.8
0.8
0.7
6 LEDs
ILED (A)
ILED (A)
Mod C
4 LEDs
0.4
0.2
0.7
Mod B
0.4
0.2
Mod A
8 LEDs
0.0
80
90
100
110
120
130
0.0
140
Original
80
LINE VOLTAGE (VRMS)
90
100
110
120
130
140
LINE VOLTAGE (VRMS)
30131189
30131190
Power Factor vs. Line Voltage
Original Circuit
Output Power vs. Line Voltage
Original Circuit
1.000
15
0.996
12
POUT (W)
POWER FACTOR
AN-2082
Typical Performance Characteristics
0.992
0.988
4 LEDs
90
100
110
120
130
3
140
LINE VOLTAGE (VRMS)
80
90
100
110
120
130
140
LINE VOLTAGE (VRMS)
30131191
www.national.com
6 LEDs
6
0.984
0.980
80
8 LEDs
9
30131193
6
Power MOSFET Drain Voltage Waveform
(VIN = 120VRMS, 6 LEDs, ILED = 350mA)
15
Mod C
POUT (W)
12
Mod B
9
6
Mod A
3
30131196
Original
80
90
100
110
120
130
140
LINE VOLTAGE (VRMS)
30131194
Current Sense Waveform
(VIN = 120VRMS, 6 LEDs, ILED = 350mA)
FILTER Waveform
(VIN = 120VRMS, 6 LEDs, ILED = 350mA)
30131197
30131198
Note 1: Original Circuit: R14 = 1.50Ω; Modification A: R14 = 1.21Ω; Modification B: R14 = 1.00Ω; Modification C: R14 = 0.75Ω
7
www.national.com
AN-2082
Output Power vs. Line Voltage
Modified Circuits
AN-2082
PCB Layout
30131109
Top Layer
30131110
Bottom Layer
www.national.com
8
AN-2082
Transformer Design
Mfg: Wurth Electronics, Part #: 750311553 Rev. 01
30131199
30131114
9
www.national.com
AN-2082
The 120 Hz current ripple flowing through the LED string was
measured to be 170 mApk-pk at full load. The magnitude of the
ripple is a function of the value of energy storage capacitors
connected across the output port. The ripple current can be
reduced by increasing the value of energy storage capacitor
or by increasing the LED string voltage.
The LED driver switching frequency is measured to be close
to the specified 79 kHz. The circuit operates with a constant
duty cycle of 0.28 and consumes 9.25 W of input power. The
driver steady state performance for an LED string consisting
of 6 series LEDs is summarized in the following table.
Experimental Results
The LED driver is designed to accurately emulate an incandescent light bulb and therefore behave as an emulated
resistor. The resistor value is determined based on the LED
string configuration and the desired output power. The circuit
then operates in open-loop, with a fixed duty cycle based on
a constant on-time and constant off-time that is set by selecting appropriate circuit components.
Performance
In steady state, the LED string voltage is measured to be
21.38 V and the average LED current is measured as 357 mA.
Measured Efficiency and Line Regulation (6 LEDs)
VIN (VRMS)
IIN (mARMS)
PIN(W)
VOUT (V)
ILED (mA)
POUT (W)
Efficiency (%) Power Factor
90
60
5.37
20.25
216
4.38
81.6
0.9970
95
63
5.95
20.47
238
4.87
81.8
0.9969
100
66
6.57
20.67
260
5.38
81.9
0.9969
105
69
7.23
20.86
285
5.94
82.1
0.9969
110
72
7.89
21.05
309
6.50
82.3
0.9968
115
75
8.59
21.23
334
7.09
82.5
0.9967
120
77
9.25
21.38
357
7.65
82.7
0.9965
125
80
9.94
21.53
382
8.23
82.8
0.9961
130
82
10.62
21.68
406
8.80
82.9
0.9957
135
84
11.26
21.80
428
9.34
83.0
0.9950
LED Current, Output Power versus Number of LEDs for Various Circuit Modifications ( VIN = 120 VAC)
# of LEDs
Original Circuit (Note 2)
Modification A (Note 2)
Modification B (Note 2)
Modification C (Note 2)
ILED (mA)
POUT (W)
ILED (mA)
POUT (W)
ILED (mA)
POUT (W)
ILED (mA)
POUT (W)
4
508
7.57
624
9.55
710
11.05
835
13.24
6
357
7.65
440
9.58
500
11.02
590
13.35
8
277
7.69
337
9.59
382
11.00
445
13.00
Note 2: Original Circuit: R14 = 1.50Ω; Modification A: R14 = 1.21Ω; Modification B: R14 = 1.00Ω; Modification C: R14 = 0.75Ω
design also exhibits low current harmonics as a percentage
of the fundamental current (as shown in the following figure)
and therefore meets the requirements of the IEC 61000-3-2
Class-3 standard.
Power Factor Performance
The LED driver is able to achieve close to unity power factor
(P.F. ~ 0.99) which meets Energy Star requirements. This
30131195
Current Harmonic Performance vs. EN/IEC61000-3-2 Class C Limits
www.national.com
10
AN-2082
Electromagnetic Interference (EMI)
The EMI input filter of this evaluation board is configured as
shown in the following circuit diagram.
30131167
FIGURE 1. Input EMI Filter and Rectifier Circuit
In order to get a quick estimate of the EMI filter performance,
only the PEAK conductive EMI scan was measured and the
data was compared to the Class B conducted EMI limits published in FCC – 47, section 15.
30131177
FIGURE 2. Peak Conductive EMI scan per CISPR-22, Class B Limits
If an additional 33nF of input capacitance (i.e. C6) is utilized
in the input filter, the EMI conductive performance is further
improved as shown in the following figure.
30131178
FIGURE 3. Peak Conductive EMI scan with additional 33nF of input capacitance
11
www.national.com
AN-2082
ILED = 350 mA
# of LEDs = 6
POUT = 7.3 W
The results are shown in the following figures.
Thermal Analysis
The board temperature was measured using an IR camera
(HIS-3000, Wahl) while running under the following conditions:
VIN = 120 VRMS
30131175
FIGURE 4. Top Side Thermal Scan
30131176
FIGURE 5. Bottom Side Thermal Scan
www.national.com
12
Injecting line voltage into FILTER (achieving PFC > 0.99)
If a small portion (750mV to 1.00V) of line voltage is injected
at FILTER of the LM3444, the circuit is essentially turned into
a constant power flyback as shown in Figure 6.
30131118
FIGURE 7. FILTER Waveform
For this evaluation board, the following resistor values are
used:
R2 = R7 = 309kΩ
R15 = 3.48kΩ
Therefore the voltages observed on the FILTER pin will be as
follows for listed input voltages:
For VIN = 90VRMS, VFILTER = 0.71V
For VIN = 120VRMS, VFILTER = 0.95V
For VIN = 135VRMS, VFILTER = 1.07V
Using this technique, a power factor greater than 0.99 can be
achieved without additional passive active power factor control (PFC) circuitry.
30131117
FIGURE 6. Line Voltage Injection Circuit
The LM3444 works as a constant off-time controller normally,
but by injecting the 1.0V rectified AC voltage into the FILTER
pin, the on-time can be made to be constant. With a DCM
Flyback, Δi needs to increase as the input voltage line increases. Therefore a constant on-time (since inductor L is
constant) can be obtained.
30131116
FIGURE 8. Typical Operation of FILTER Pin
13
www.national.com
AN-2082
By using the line voltage injection technique, the FILTER pin
has the voltage wave shape shown in Figure 7 on it. Voltage
at VFILTER peak should be kept below 1.25V. At 1.25V current
limit is tripped. C11 is small enough not to distort the AC signal
but adds a little filtering.
Although the on-time is probably never truly constant, it can
be observed in Figure 8 how (by adding the rectified voltage)
the on-time is adjusted.
Circuit Analysis and Explanations
LM3444 - 120VAC, 8W Isolated Flyback LED Driver
Notes
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AN-2082
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LM3401,LM3402,LM3402HV,LM3404,LM3404HV,
LM3405,LM3405A,LM3406,LM3406HV,LM3407,
LM3409,LM3409HV,LM3410,LM3414,LM3414HV,
LM3421,LM3423,LM3424,LM3429,LM3430,
LM3431,LM3433,LM3434,LM3435,LM3444,
LM3445,LM3450,LM3464,LM3492,LM5022
Application Note 1656 Design Challenges of Switching LED Drivers
Literature Number: SNVA253
National Semiconductor
Application Note 1656
Chris Richardson
October 2007
Using a switching regulator as an LED driver requires the designer to convert a voltage regulator into a current regulator.
Beyond the challenge of changing the feedback system to
control current, the LEDs themselves present a load characteristic that is much different than the digital devices and other
loads that require constant voltage. The LED WEBENCH®
online design environment predicts and simulates the response of an LED to constant current while taking into account several potential design parameters that are new to
designers of traditional switching regulators.
Once the VF of the LEDs has been determined from the V-I
curve, the LED driver’s output voltage is calculated using the
following formula:
VO = n x VF + VSNS
In this equation, 'n' is the number of LEDs connected in series,
and 'VSNS' is the voltage drop across the current sense resistor.
Output Voltage Changes when LED
Current Changes
In the first step of the LED WEBENCH tool, "Choose Your
LEDs", an LED is selected with a standard forward current,
IF. This default value is provided by the LED manufacturers,
and in most cases it represents the testing condition for that
LED. Typical values for high-power LEDs are 350 mA, 700
mA, and 1000 mA.
Designing for VO-MIN and VO-MAX
In practice, the typical value of VF changes with forward current. Further analysis of total output voltage is needed because VF also changes with process and with the LED die
temperature. The more LEDs in series, the larger the potential
difference between VO-MIN, VO-TYP and VO-MAX. An LED driver
must therefore be able to vary output voltage over a wide
range to maintain a constant current. IF is the controlled parameter, but minimum and maximum output voltage must be
predicted in order to select the proper regulator topology, IC,
and passive components.
Design Challenges of Switching LED Drivers
Design Challenges of
Switching LED Drivers
30025102
30025101
FIGURE 1. V-I Curve with Typical VF and IF
Not all designs will use a standard current, however. The designer can select a different LED current, and then the forward
voltage will change in the VLED box under step 2. The change
in voltage comes from LEDs’ V-I curve. Figure 1 shows a
curve from a 5W white (InGaN) LED that differs from the
curves normally found in LED datasheets. LED manufacturers provide these curves, but they are often shown as I-V
curves with voltage as the independent quantity. In Figure 1,
forward current is the independent variable, reflecting the fact
that in LED drivers current is controlled, and voltage is allowed
to vary. The cross-hairs intersect at the standard/typical IF and
VF values of 350 mA and 3.5V, respectively.
FIGURE 2. VIN-MIN > VO-TYP, Buck Regulator Works
A typical example that can lead to trouble is driving three white
(InGaN) LEDs from an input voltage of 12V ±5%. In Figure
2, each LED operates at the typical VF of 3.5V, and the current
sense adds 0.2V for a VO of 10.7V. Minimum input voltage is
95% of 12V, or 11.4V, meaning that a buck regulator capable
of high duty cycle could be used to drive the LEDs.
However, a buck regulator designed for the typical VO will be
unable to control IF if VO-MAX exceeds the minimum input voltage. The same white LEDs with a typical VF of 3.5V have a
VF-MAX of 4.0V. Headroom is tight under typical conditions,
and the buck regulator will lose regulation with only a small
increase in VF from one or more of the LEDs (Figure 3).
AN-1656
WEBENCH® is a registered trademark of National Semiconductor Corporation.
© 2007 National Semiconductor Corporation
300251
www.national.com
AN-1656
To maintain safety and reliability in a parallel LED system,
forward voltage should be binned or matched. Fault monitoring should detect LEDs that fail as either short or open circuits.
Finally, the entire array should have evenly distributed heat
sinking, to ensure that VF change with respect to die temperature occurs uniformly over all the LEDs.
Selecting LED Ripple Current
LED ripple current, ΔiF, in an LED driver is the equivalent of
output voltage ripple, ΔvO, in a voltage regulator. In general,
the requirements for ΔiF are not as tight as output voltage ripple. Where a ripple of a few milivolts to 4%P-P of VO is typical
for ΔvO, ripple currents for LED drivers range from 10% to
40%P-P of the average forward current, IF.Figure 5 and Figure
6 show a typical ripple current of 25%P-P from a buck switching
LED driver. A wider tolerance for ΔiF is acceptable because
the ripple is too high in frequency for the human eye to see.
General illumination applications (Such as lamps, flashlights,
signs, etc.) can tolerate large ripple currents without harming
the quality or character of the light. Allowing larger ripple current means lower inductance and capacitance for the output
filter, which in turn translates to smaller PCB footprints and
lower BOM costs. For this reason, ΔiF should generally be
made as large as the application permits.
The true upper limit for ΔiF comes from the nonlinear proportion of heat to light that is generated as the peak current
through the LED increases. Above approximately 40%P-P ripple, the LED can experience more heating during the peaks
than cooling during the valleys, resulting in higher die temperature and reduction in LED lifetime.
Some high-end applications require tighter control over LED
ripple current. These include industrial inspection, machine
vision, and blending of red, green, and blue for backlighting
or video projection. The higher system cost of these applications justifies larger, more expensive filtering to achieve ripple
currents in the sub 10%P-P region.
30025103
FIGURE 3. VIN-MIN < VO-MAX, Buck Regulator Fails to
Regulate
Pitfalls of Parallel LED Arrays
Whenever LEDs are placed in parallel, the potential exists for
a mismatch in the current that flows through the different
branches. The forward voltage, VF, of each LED varies with
process, so unless each LED is binned or selected to match
VF, the LED or LED string with the lowest total forward voltage
will draw the most current (Figure 4). This problem is compounded by the negative temperature coefficient of LEDs
(and all PN junction diodes). The LEDs that draw the most
current suffer the greatest increase in die temperature. As
their die temperature increases, their VF decreases, creating
a positive feedback loop. Elevated die temperature both reduces the light output and decreases the lifetime of the LEDs.
The system in Figure 4 also illustrates a potential over-current
condition if one of the LEDs fails as an open circuit. Without
some protection scheme, the entire drive current IO will flow
through the remaining LED(s), likely causing thermal overstress. Likewise, if one of the LEDs fails as a short circuit, the
total forward voltage of that string will drop significantly, causing higher current to flow through the affected branch.
30025105
FIGURE 5. LED Current (DC and AC)
30025104
FIGURE 4. Mismatched LEDs in Parallel
www.national.com
2
AN-1656
30025106
FIGURE 6. Only LED Ripple Current
30025107
FIGURE 7. VF vs IF
Dynamic Resistance
Load resistance is an important parameter in power supply
design, particularly for the control loop. In LED drivers it is also
used to select the output capacitance needed to achieve the
desired LED ripple current. In a standard power supply that
regulates output voltage, the load resistance has a simple
calculation:
RO = VO / IO
When the load is an LED or string of LEDs, however, the load
resistance is replaced with the dynamic resistance, rD and the
current sense resistor. LEDs are PN junction diodes, and their
dynamic resistance shifts as their forward current changes.
Dividing VF by IF leads to incorrect results that are 5 to 10
times higher than the true rD value.
Typical dynamic resistance at a specified forward current is
provided by some manufacturers, but in most cases it must
be calculated using I-V curves. (All LED manufacturers will
provide at least one I-V curve.) To determine rD at a certain
forward current, draw a line tangent to the I-V slope as shown
in Figure 7. Extend the line to the edges of the plot and record
the change in forward voltage and forward current. Dividing
ΔVF by ΔIF provides the rD value at that point. Figure 8 shows
a plot of several rD values plotted against forward current to
demonstrate how much rD shifts as the forward current
changes.
One amp is a typical driving current for 3W LEDs, and the
calculation below shows how the dynamic resistance of a 3W
white InGaN was determined at 1A:
30025108
FIGURE 8. rD vs IF
Dynamic resistances combine in series and parallel like linear
resistors, hence for a string of 'n' series-connected LEDs the
total dynamic resistance would be:
rD-TOTAL = n x rD + RSNS
A curve-tracer capable of the 1A+ currents used by high power LEDs can be used to draw the I-V characteristic of an LED.
If the curve tracer is capable of high current and high voltage,
it can also be used to draw the complete I-V curve of the entire
LED array. Total rD can determined using the tangent-line
method from that plot. In the absence of a high-power curve
tracer, a laboratory bench-top power supply can be substituted by driving the LED or LED array at several forward currents
and measuring the resulting forward voltages. A plot is created from the measured points, and again the tangent line
method is used to find rD.
ΔVF = 3.85V – 3.48V
ΔIF = 1.5A – 0A
rD = ΔVF / ΔIF = 0.37 / 1.5 = 0.25Ω
3
www.national.com
Design Challenges of Switching LED Drivers
Notes
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(“NATIONAL”) PRODUCTS. NATIONAL MAKES NO REPRESENTATIONS OR WARRANTIES WITH RESPECT TO THE ACCURACY
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PARAMETERS OF EACH PRODUCT IS NOT NECESSARILY PERFORMED. NATIONAL ASSUMES NO LIABILITY FOR
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Life support devices or systems are devices which (a) are intended for surgical implant into the body, or (b) support or sustain life and
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AN-1656
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National Semiconductor
2900 Semiconductor Dr.
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M Reynolds, David Zhang
Applications Engineer
SSL Division - Longmont,
CO 80501
LM3444 MR16 Boost Reference Design for
Non-Dimming & Dimming LED Applications
March 31, 2011
Revision 1.0a
NATIONAL SEMICONDUCTOR
Page 1 of 20
Table of Contents
MR16 Halogen/SSL Retro-Fit Analysis ...................................................................................................................... 3
Differences between Magnetic and Electronic Transformers .................................................................................................... 3
SSL MR16 lamps compatibility concerns with ELVT and ELV dimmers (true retro-fit) ............................................................... 3
Halogen vs SSL MR16 waveforms ............................................................................................................................................... 4
Halogen MR16 .............................................................................................................................................................. 5
LM3444 MR16 Boost Reference Design .................................................................................................................... 7
Operating Specifications ............................................................................................................................................................. 7
Schematic.................................................................................................................................................................................... 8
PCB Layout .................................................................................................................................................................................. 8
Bill of Materials ........................................................................................................................................................................... 9
Typical Performance ................................................................................................................................................................ 10
Dimming Waveforms ................................................................................................................................................................ 13
Thermal Analysis .......................................................................................................................................................15
Reference Design Transformer Compatibility ........................................................................................................16
Performance with and without Transformer ...........................................................................................................17
Revision History .........................................................................................................................................................20
LM3444-MR16-Boost Reference Design
NATIONAL SEMICONDUCTOR
Page 2 of 20
MR16 Halogen/SSL Retro-Fit Analysis
Differences between Magnetic and Electronic Transformers
Magnetic Transformers
Magnetic transformers step down 120VAC line voltage to 12VAC. Magnetic transformers consist only of magnetic
core, and copper wire, no electronics are used to step down the voltage from 120VAC to 12VAC. Due to the fact
that the frequency of operation is 50Hz or 60Hz, the size of the Magnetic transformers is large and heavy. Magnetic
transformers are primarily available in two types of construction; torroidal and laminated EI core.
With existing Halogen MR16 systems that require dimming, Magnetic Low Voltage Dimmers are required to be
used.
Electronic Transformers
Electronic transformers also step down 120VAC line voltage to 12VAC. Electronic transformers are much smaller
and more efficient than magnetic transformers. Electronic transformers are more common than magnetic
transformers in existing Halogen MR16 system. Electronic Low Voltage Transformers (ELVT) consists of a small
self resonant tank power supply. Electronic Low Voltage Dimmers (ELV dimmers) are used with ELVT for dimming
systems.
Although electronic transformers are more complex, with many more components, that their magnetic counterparts,
electronic transformers are far less expensive and smaller. The shear amount of core material and copper within a
magnetic transformer adds cost, and the weight of the product makes it expensive to manufacture, and ship.
SSL MR16 lamps compatibility concerns with ELVT and ELV dimmers (true retro-fit)
Electronic transformers modulate (PWM) the input AC voltage with a frequency of 35 kHz to150 kHz. This
waveform is step-down from 120V or 230V (typical) to 12VAC with a transformer. The higher switching frequency
allows for the smaller magnetic components, and the overall smaller design. As mentioned earlier, the electronic
transformer is a self driven resonant half bridge topology. The self resonance half-bridge topology requires the
converter to have a minimal load at all times to function properly. Common minimum loads for ELV dimmers are
from 6W – 12W depending on manufacture, and maximum power rating of the ELVT. With traditional Halogen
lamps, the minimal load is of no concern, common Halogen MR16 lamps use about 50W of power per lamp. These
lamps are very inefficient, and 10W of Halogen power produces very little light.
With the current efficacy of the LEDs above 100 lumens per watt, 6W of SSL power is equivalent to about 40W to
50W of Halogen power. One can quickly see the compatibility issue of SSL MR16 lamps and the ELVT’s. If the
output power of the ELVT reduces below the minimum requirement, the ELV dimmer will stop operating. The
turning on, and off of the ELVT will cause visible flicker from the SSL MR16 lamp, and could also cause reliability
issues with the lamp or ELVT.
LM3444-MR16-Boost Reference Design
NATIONAL SEMICONDUCTOR
Page 3 of 20
Halogen vs SSL MR16 waveforms
Halogen MR16 waveforms



Improper SSL MR16 operating waveform
Channel - 1 (yellow trace) = Input line voltage
Channel - 3 (purple trace) = Input line current
Channel - 4 (green trace) = bulb current
Issue #1 - The two scope captures above illustrate the SSL MR16 technical challenges. Figure one shows typical
Halogen MR16 waveforms, and figure two is common MR16 replacement bulbs waveforms. The SSL replacement
bulb looks capacitive to the ELVT; therefore large current spikes charge the energy storage device within the SSL
MR16 bulb. The switching converter within the bulb then processes the input power from the energy storage
element to the LED load. At this time the minimum load requirement of the ELVT is not satisfied, and the ELVT
turns off. Once the energy is depleted within the MR16 converter, the ELVT will start up, and the process cycles.
The turning off/on of the ELVT will manifest itself as visible flicker.
Issue #2 – The maximum input current to the Halogen bulb is approximately 4.25A. The maximum input current to
the SSL bulb is approximately 12A. The large magnitude spike associated with charging the SSL MR16 input
capacitor can cause premature failures within the SSL bulb, or even the ELVT.
LM3444-MR16-Boost Reference Design
NATIONAL SEMICONDUCTOR
Page 4 of 20
Halogen MR16
Summary: No flickering observed. There is a delay (1.12ms, 24° angle) from when the supply voltage starts
ramping up from zero volts to when the electronic transformer starts to operate and the bulb turns on. This delay
shows up on the LED MR16s as well although the magnitude of delay does vary from bulb to bulb. No current
spikes observed out of the transformer.
The bench set-up diagram below was used in the evaluation of the halogen MR16 bulb. The following scope plots
show voltage and current waveforms designated by the labels indicated in the bench set-up diagram. The
electronic transformer used was the Lightech LET-75.
Bench Circuit
IIN
LINE
120VAC
Power
Supply
LINE
VIN
NEUTRAL
+12V
12V, 50W Halogen
MR16 Bulb
IBULB
Transformer
(Electronic)
NEUTRAL
SGND
VBULB
VIN (Yellow), IIN (Magenta), IBULB (Green)
LM3444-MR16-Boost Reference Design
NATIONAL SEMICONDUCTOR
Page 5 of 20
VIN (Yellow), IIN (Magenta), IBULB (Green)
VBULB (Blue), IBULB (Green)
LM3444-MR16-Boost Reference Design
NATIONAL SEMICONDUCTOR
Page 6 of 20
LM3444 Boost MR16 Reference Design
This reference design was based on the released LM3444 IC from National Semiconductor.
This design was developed to minimize the current spikes coming out of an electronic transformer to less than 5A,
which is a typical transformer rating, when driving an LED MR16 circuit. The off the shelf LED MR16 solutions
exhibit spikes that significantly exceed a transformer’s maximum rated output current which will degrade the
reliability of the transformer and reduce its operating lifetime.
This design generates a continuous LED current when a 220uF 35V electrolytic capacitor is placed across the
output. The circuit operates in a constant output power mode. The output power is fixed at about 6W.
Operating Specifications
NOTE: The following specifications are typical values based on the LED driver being powered directly by a 12VAC
supply (i.e. no electronic or magnetic step-down transformer).
Input Voltage, VIN: ............................................................................................................................................. 12 VAC
Output Voltage, VOUT: ................................................................................................... 23.5V (Single string of 7 LEDs)
Input Current, IIN .................................................................................................................................................. 710mA
LED Output Current, ILED ..................................................................................................................................... 280mA
Input Power, PIN .................................................................................................................................................. ~ 8.0W
Output Power, POUT ............................................................................................................................................. ~ 6.6W
Efficiency ............................................................................................................................................................. ~ 83 %
Power Factor ........................................................................................................................................................ ~ 0.95
Input Voltage, VIN: ............................................................................................................................................. 12 VAC
Output Voltage, VOUT: ................................................................................................... 26.6V (Single string of 8 LEDs)
Input Current, IIN .................................................................................................................................................. 680mA
LED Output Current, ILED ..................................................................................................................................... 240mA
Input Power, PIN .................................................................................................................................................. ~ 7.7W
Output Power, POUT ............................................................................................................................................. ~ 6.4W
Efficiency ............................................................................................................................................................. ~ 83 %
Power Factor ........................................................................................................................................................ ~ 0.95
Input Voltage, VIN: ............................................................................................................................................. 12 VAC
Output Voltage, VOUT: ................................................................................................... 28.2V (Single string of 9 LEDs)
Input Current, IIN .................................................................................................................................................. 670mA
LED Output Current, ILED ..................................................................................................................................... 220mA
Input Power, PIN .................................................................................................................................................. ~ 7.5W
Output Power, POUT ............................................................................................................................................. ~ 6.2W
Efficiency ............................................................................................................................................................. ~ 83 %
Power Factor ........................................................................................................................................................ ~ 0.95
SMPS Topology .................................................................................................................................................... Boost
LM3444-MR16-Boost Reference Design
NATIONAL SEMICONDUCTOR
Page 7 of 20
PCB Schematic
PCB Layout
LM3444-MR16-Boost Reference Design
NATIONAL SEMICONDUCTOR
Page 8 of 20
Bill of Materials
Designator
Description
MFG
Part Number
C1
CAP, CERM, 1.0uF, 25V, +/-10%, X5R, 0805
MuRata
GRM216R61E105KA12D
C2
CAP, ELECT, 220uF, 35V, +/-20%, Radial 8x11.5mm
Panasonic
ECA-1VHG221
C3
CAP, CERM, 22uF, 25V, +/-10%, X5R, 1210
MuRata
GRM32ER61E226KE15L
C4
CAP, CERM, 330pF, 100V, +/-5%, X7R, 0603
AVX
06031C331JAT2A
C5
CAP, CERM, 4.7uF, 50V, +/-10%, X7R, 1210
MuRata
GRM32ER71H475KA882
C6
CAP, CERM, 4.7uF, 25V, +/-10%, X5R, 0805
MuRata
GRM21BR61E475KA12L
D1-D4
Diode, Schottky, 30V, 3A, SMA
Diodes Inc.
B330A-13-F
D5
Diode, Schottky, 60V, 1A, SMA
Diodes Inc.
B160-13-F
D6
TVS BI-DIR 24V 400W SMA (Optional)
Diodes Inc
SMAJ24CA-13-F
D7
Diode, Zener, 11V, 500mW, SOD-123
Central Semiconductor
CMHZ4698
D8
Diode, Zener, 33V, 500mW, SOD-123
Central Semiconductor
CMHZ4714
L1
Ind, Shielded Drum Core, Ferrite, 33uH, 1.1A, 0.31 ohm, SMD
Coilcraft
MSS6132-333MLB
Q1
Transistor, NPN, 80V, 500mA, SOT-23
Central Semiconductor
CMPTA06
Q2
MOSFET, N-CH, 60V, 1.2A, SOT-23
Diodes Inc.
ZXMN6A07FTA
R1
RES, 0.1 ohm, 5%, 0.125W, 0805
Panasonic
ERJ-6RSJR10V
R2, R4
RES, 1.00k ohm, 1%, 0.1W, 0603
Vishay-Dale
R3
RES, 12.4k ohm, 1%, 0.1W, 0603
Vishay-Dale
CRCW06031K00FKEA
ERJ-6GEYJ4R7V
CRCW060312k4FKEA
R5
RES, 1.00 ohm, 1%, 0.5W, 1206
Stackpole Electronics Inc
CSR1206FK1R00
R6
RES, 4.7 ohm, 5%, 0.125W, 0805
Yageo
RC0805JR-074R7L
U1
AC-DC Off Line LED Driver
National Semiconductor
LM3444MM
LM3444-MR16-Boost Reference Design
NATIONAL SEMICONDUCTOR
Page 9 of 20
Typical Performance (Eight series LEDs)
Bench Circuit
I1
LINE
120VAC
Power
Supply
NEUTRAL
I3
I2
Vp
Vs
Transformer
V1
(Electronic)
Vp
Vs
VIN
V2
LM3444 MR16
LED Driver
VIN
LED
Board
LED+
V3
LED-
The following scope plots show voltage and current waveforms designated by the labels indicated in the following
bench set-up diagram. The electronic transformer used was the Lightech LET-75.
CH2 V1 Voltage, CH4 I3 Current
LM3444-MR16-Boost Reference Design
NATIONAL SEMICONDUCTOR
Page 10 of 20
CH2 V1 Voltage, CH4 I2 Current
4.4A peak
CH2 V1 Voltage, CH4 I2 Current
LM3444-MR16-Boost Reference Design
NATIONAL SEMICONDUCTOR
Page 11 of 20
CH2 V2 Voltage, CH4 I2 Current
LM3444-MR16-Boost Reference Design
NATIONAL SEMICONDUCTOR
Page 12 of 20
LM3444 MR16 Boost evaluation board Dimming Waveforms
Bench Circuit
I1
Vp
LINE
120VAC
Power
Supply
V1
Triac
Dimmer
V2
NEUTRAL
I4
I3
I2
Vs
Transformer
( Electronic )
Vp
Vs
VIN
V3
VIN
LED
Board
LED+
LM3444 MR16
LED Driver
V4
LED-
This LM3444 MR16 Boost evaluation board is designed to operate (flicker-free) with common Electronic Low
Voltage dimmers, and Electronic Transformers.
Dimmer Used – Lutron SELV-300P-GR
Electronic Transformer – Lightech LET75
20:1 dimming ratio
LM3444 MR16 Boost - Eight series connected LEDs at 200mA (90° Conduction Angle)
CH2 V2 Voltage, CH4 I4 Current
LM3444-MR16-Boost Reference Design
NATIONAL SEMICONDUCTOR
Page 13 of 20
LM3444 MR16 Boost - Eight series connected LEDs at 100mA (45° Conduction Angle)
CH2 V2 Voltage, CH4 I4 Current
LM3444 MR16 Boost - Eight series connected LEDs at 10mA (minimum Conduction Angle)
CH2 V2 Voltage, CH4 I4 Current
LM3444-MR16-Boost Reference Design
NATIONAL SEMICONDUCTOR
Page 14 of 20
Thermal Analysis
LM3444-MR16-Boost Reference Design
NATIONAL SEMICONDUCTOR
Page 15 of 20
Reference Design Transformer Compatibility
The following transformers were tested with the National LED driver designs described in this document. A
compatibility matrix is shown below which describes which driver/transformer combinations are suitable (i.e. no
flicker, stable operation).
Electronic Transformers (120VAC to 12VAC):
Lightech, Model: LET-60, 60W
Lightech, Model: LET-75, 75W
Lightech, Model: LET-60 LW, 60W
Hatch, Model: RS12-80M, 80W
Hatch, Model: RS12-60, 60W
Pony, Model: PET-120-12-60, 60W
Eurofase, Model: 0084 CLASS 2, 60W
Magnetic Transformers (120VAC to 12VAC):
Hatch, Model: LS1275EN, 75VA
LM3444-MR16-Boost Reference Design
NATIONAL SEMICONDUCTOR
Page 16 of 20
Performance with 7 LEDs
Performance without transformer
The table below compares the performance of each reference design when powered directly by a 12VAC source
LM3441 BOOST 7 LEDs
11.91
0.708
7.97
23.55
0.281
6.62
83.0%
0.948
Units
VAC
A
W
VDC
A
W
-
Specs
VIN
IIN
PIN
(1)
VOUT
(1)
ILED
(2)
POUT
Efficiency
Power Factor
LM3444 BOOST 7 LEDs
120
0.07
8.18
23.5
0.270
6.23
77.6%
0.970
Units
VAC
A
W
VDC
A
W
-
Specs
VIN
IIN
PIN
VOUT
ILED
POUT
Efficiency
Power Factor
LM3444 BOOST 7 LEDs
2 LEDs
120@ 1A
0.072
8.13
23.5
0.270
6.23
78.0%
0.934
Units
VAC
A
W
VDC
A
W
-
Specs
VIN
IIN
PIN
(1)
VOUT
(1)
ILED
(2)
POUT
Efficiency
Power Factor
Performance with transformer
LET-75
HATCH RS12-80M
LM3444-MR16-Boost Reference Design
NATIONAL SEMICONDUCTOR
Page 17 of 20
Performance with 8 LEDs
Performance without transformer
The table below compares the performance of each reference design when powered directly by a 12VAC source
LM3441 BOOST 8 LEDs
11.91
0.682
7.66
26.64
0.238
6.34
82.8%
0.946
Units
VAC
A
W
VDC
A
W
-
Specs
VIN
IIN
PIN
VOUT
ILED
POUT
Efficiency
Power Factor
LM3444 BOOST 8 LEDs
120
0.067
7.86
26.5
0.230
6.10
77.5%
0.970
Units
VAC
A
W
VDC
A
W
-
Specs
VIN
IIN
PIN
VOUT
ILED
POUT
Efficiency
Power Factor
LM3444 BOOST 8 LEDs
2 LEDs
120@ 1A
0.069
7.82
26.5
0.230
6.10
77.9%
0.930
Units
VAC
A
W
VDC
A
W
-
Specs
VIN
IIN
PIN
(1)
VOUT
(1)
ILED
(2)
POUT
Efficiency
Power Factor
Performance with transformer
LET-75
HATCH RS12-80M
LM3444-MR16-Boost Reference Design
NATIONAL SEMICONDUCTOR
Page 18 of 20
Performance with 9 LEDs
Performance without transformer
The table below compares the performance of each reference design when powered directly by a 12VAC source
LM3441 BOOST 9 LEDs
11.92
0.668
7.51
28.25
0.220
6.22
82.8%
0.946
Units
VAC
A
W
VDC
A
W
-
Specs
VIN
IIN
PIN
VOUT
ILED
POUT
Efficiency
Power Factor
LM3444 BOOST 9 LEDs
120
0.066
7.74
28.0
0.215
6.02
77.8%
0.970
Units
VAC
A
W
VDC
A
W
-
Specs
VIN
IIN
PIN
VOUT
ILED
POUT
Efficiency
Power Factor
LM3444 BOOST 9 LEDs
2 LEDs
120@ 1A
0.068
7.64
28.0
0.212
5.94
77.7%
0.930
Units
VAC
A
W
VDC
A
W
-
Specs
VIN
IIN
PIN
(1)
VOUT
(1)
ILED
(2)
POUT
Efficiency
Power Factor
Performance with transformer
LET-75
HATCH RS12-80M
LM3444-MR16-Boost Reference Design
NATIONAL SEMICONDUCTOR
Page 19 of 20
Revision History
Date
Author
Revision
LM3444-MR16-Boost Reference Design
Description
NATIONAL SEMICONDUCTOR
Page 20 of 20
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