Dimmable 120 Vac, 6.5 W Input Parallel-to-Series Lighting Circuit

DN05084/D
Design Note – DN05084/D
Dimmable 120 Vac, 6.5 W Input
Parallel-to-Series Lighting Circuit
Application
LED Lighting,
AC
Input
Voltage
110 to 130 Vac
Topology
Efficiency
Input Power
Power
Factor
THD
Parallel-toSeries
77%
6.8 W
0.99
17.2%
Figure 1 – Two-Stage Parallel-to-Series LED Lighting Circuit, with Switch-In CCR, available as evaluation board
40WBULBGEVB
Key Features









All of the LEDs are equally bright and can be distributed apart from each other such as in a T8 tube
Dimmable with standard Triac dimmers without wasteful active bleeding
Power factor = 0.99
THD below 20%
Adjustable for different total LED voltages between 135 and 145 volts by changing a single resistor (R3)
Thermal foldback; regulated current decreases as temperature increases
Temperature compensated control circuitry
Tested and proven from -40 °C to 85 °C in temperature chamber with minimal input power variation
Meets EN55022 AV EMI standard without filter (no magnetics required)
June 2016, Rev. 1
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1
DN05084/D
Schematic
Figure 2 – Two-Stage Parallel-to-Series LED Lighting Circuit, with Switch-In CCR. It is possible to mount an
inductor (L1) and a capacitor on the board for additional EMI filtering, but generally these are not needed. Inductor
L1 has a 0 ohm resistor in its place on the evaluation board.
Circuit Operation
This circuit is an enhanced parallel-to-series LED lighting circuit. It uses updated control circuitry that allows the
ability to accommodate multiple LED voltages by simply adjusting a single resistor (R3) as well as compensating
for drift in LED voltage with temperature. It also has superb PF, THD performance, dimmability, and efficiency at
a low cost.
ON Semiconductor’s parallel-to-series topology dynamically adjusts LED load voltage as the instantaneous
bridge output voltage varies. While a switch-mode power supply (a buck converter) reconfigures the input
voltage to match the load, this circuit reconfigures the load to match the input voltage. When the instantaneous
input voltage is relatively low, the LEDs are configured in parallel. When the instantaneous input voltage is
relatively high, the LEDs are configured in series.
The circuit is designed for input voltages between 100 VAC and 140 VAC . ON Semiconductor CCRs are used to
provide constant LED current and to protect LEDs from over-voltage conditions. The circuit employs an additional
CCR (shown as CCR2) to increase LED current at high voltages for improved PF and THD performance.
June 2016, Rev. 1
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DN05084/D
Figure 3 – The LED configuration is dynamically adjusted by the control circuitry depending on the instantaneous
AC input voltage.
How to Adjust the Driver for Different LEDs
For demonstration purposes, this circuit is configured with six LEDs that have a nominal forward voltage of 24 V.
The recommended range for the total voltage of all LEDs combined for this type of circuit is 135 to 145 V. This
range is approximate, but will allow for the best efficiency and dimmability.
Use an oscilloscope to probe the voltage across CCR1 and CCR3. CCR1 and CCR3 should run with their
anode-cathode voltage (VAK) at 3 to 6 volts as the LEDs switch from parallel-to-series. Make slight adjustments to
R3 to accomplish this. For example, the typical value for R3 will be 51k, but different LEDs may require 47k for
R3. If the CCR1 and CCR3 voltage is too high when the strings switch their configuration, the circuit will be less
efficient. If CCR1 and CCR3 Vak is too low the efficiency will improve, but some TRIAC dimmers may misfire.
The base-emitter voltage at Q2 initiates the switch from parallel-to-series. This base-emitter voltage is about 0.6
V. The total LED voltage of the six 24 V Cree LEDs in this circuit was about 142 V. R3, R4, D3, and Q2 set the
switching point.
3+4
)
4
(2) = VBE(Sat) (
51+360
)
360
= 0.6 (
= 86 V
The contribution from D3 is about 62 V, and the contribution from R3, R4, and Q2 is about 94 V. Therefore the
approximate switching point is 86 + 94 V = 148 V.
So to adjust for a lower LED voltage such as 135 V, adjust R3 lower.
3+4
)
4
(2) = VBE(Sat) (
June 2016, Rev. 1
47+360
)
360
= 0.6 (
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= 79 V
3
DN05084/D
These calculations make assumptions such as a constant and precisely measured LED voltage, so be sure to
verify with an oscilloscope that CCR1 has VAK between 3 to 6 V at the switching point. Use Table 1 as a
reference for starting values of R3.
Table 1. Suggested starting values for R3 to tune the circuit for different LED voltages.
Total LED Voltage for all LEDs in
Suggested starting value for R3 (verify CCR1 Vak with
Series
oscilloscope)
136 V
47.7 kΩ
138 V
49.0 kΩ
140 V
50.0 kΩ
142 V
51.0 kΩ
144 V
52.5 kΩ
Also be sure that CCR3 is active just above the switching point. R3 can be manipulated for this purpose if
necessary. If CCR3 is on for too long, THD will improve but efficiency will decrease slightly. To tune this,
decrease the value of R2 in 5 or 10% increments.
If CCR3 is not on for long enough, THD and efficiency will suffer. Increase the value of R2 in 5 or 10%
increments to correct this.
Figure 4 – When adjusting for different LEDs, choose R3 such that CCR1 has 3 to 6 V across it at the point the
red arrow indicates in the figure. This point is where the LEDs switch from parallel to series. When the switch
takes place the CCR1 must continue conducting, so allow for 3 to 6 V across it.
June 2016, Rev. 1
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DN05084/D
Populating L1 and C2
The evaluation board is shipped with L1 shorted as a 0 ohm resistor and C2 unpopulated. L1 and C2 form
an EMI filter. Generally EMI filtering is not needed with these circuits because they are not switching power
supplies.
Using C2 has several advantages and disadvantages. The advantages are increased EMI filtering and
surge protection, but these are not really needed for most applications. Also it ensures compatibility with some
dimmers that require a leakage path to maintain the LEDs in the off state when the dimmer’s manual switch is
turned off. Another way to provide this leakage is with a resistor, but that would decrease efficiency. We
recommend testing with and without C2 and checking whether the circuit satisfies whatever requirements are
being sought for a particular lamp. The disadvantages to C2 are the size, cost, and extra population step.
Circuit Performance Data (with small heat sink attached to LEDs)
Specification
110 VAC
120 VAC
130 VAC
IRMS(out) (mA)
38.9
48.3
53.26
Power Factor
0.979
0.985
0.988
THD Total (IRMS, %)
20.2
17.2
14.8
THD 3rd (IRMS, %)
3.59
5.66
4.4
PIN (W)
5.49
6.76
7.76
Efficiency (%)
75
77
76
Circuit Performance Data (with no heat sink for LEDs)
June 2016, Rev. 1
Specification
110 VAC
120 VAC
130 VAC
IRMS(out) (mA)
40.7
49.2
53.6
Power Factor
0.982
0.987
0.990
THD Total (IRMS, %)
18.9
16.1
13.9
THD 3rd (IRMS, %)
4.88
5.47
3.74
PIN (W)
5.67
6.86
7.82
Efficiency (%)
73
75
73
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DN05084/D
Bill of Materials
Tolerance
Footprint
Manufacturer
Manufacturer Part
Number
Substitution
Allowed
5%
0805
Any
Any
Yes
1%
0805
Any
Any
Yes
1%
0805
Any
Any
Yes
1%
0805
Any
Any
Yes
5%
0805
Any
Any
Yes
5%
0805
Any
Any
Yes
20%
0805
Any
Any
Yes
10%
Through
Hole
Wurth Electronics
Inc
890324023028
Yes
N/A
N/A
TO-269AA
Vishay
MB6S-E3/80
Yes
Diode SMD
62 Vz
5%
SOD-123
MMSZ5265BT1G
No
Diode SMD
N/A
N/A
SOD-323
Designator
Quantity
Description
R1
1
Resistor SMD
R2
1
Resistor SMD
R3
1
Resistor SMD
R4
1
Resistor SMD
R5
1
Resistor SMD
R6, R7, R8
3
Resistor SMD
C1
1
Capacitor
SMD
C2
1
X2 Film
Capacitor
BD1
1
Bridge
Rectifier
D3
1
D4
1
510k,
1/8th W
412,
1/8th W
51k,
1/8th W
360,
1/8th W
10k,
1/8th W
100k,
1/8th W
10nF,
250 V
220 nF,
275
VAC
ON
Semiconductor
ON
Semiconductor
BAS21HT1G
No
No
24V
N/A
2-SMD
Cree
XTEHVW-H0-000000000LD51
N/A
N/A
SOT-23
ON
Semiconductor
MMBT5401LT1G
No
N/A
N/A
SOT-23
ON
Semiconductor
MMBT3904LT1G
No
N/A
N/A
SOT-23
ON
Semiconductor
MMBT5551LT1G
No
120V,
30mA
15%
SMB
ON
Semiconductor
NSIC2030JB
No
120V,
20mA
15%
SMB
ON
Semiconductor
NSIC2020JB
No
Fuse SMD
1.5A,
250V
N/A
2-SMD
Littelfuse
044301.5DR
Yes
1
Varistor SMD
198V,
250A
N/A
2-SMD
Littelfuse
V220CH8T
Yes
1
Resistor SMD
0, 1/8th
W
NA
1206
Any
Any
Yes
D5-D10
6
Q1, Q5
2
Q2
1
Q3, Q4
2
CCR1,
CCR2
2
CCR3
1
F1
1
MOV1
L1
June 2016, Rev. 1
Value
SMD LED
PNP Bipolar
Transistor
SMD
NPN Bipolar
Transistor
SMD
NPN Bipolar
Transistor
SMD
Constant
Current
Regulator
SMD
Constant
Current
Regulator
SMD
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DN05084/D
Compatible with Triac Dimmers
This circuit is inherently compatible with triac dimmers. The LEDs run for a large portion of time and the
sinusoidal current draw resembles that of an incandescent bulb. In the ON Semiconductor lab the circuit was
tested with the dimmers below and found to be fully functional. Populate C2 to ensure compatibility with a small
minority of dimmers which require bleeding current even when manually switched off.
Dimmers Tested
Lutron
DVCL 153P
Lutron
DVWCL 153P
Lutron
CTCL 153P
Lutron
TECL 153P
Lutron
AYCL 153P
Lutron
5LL 153P
Lutron
LGCL 153P
Lutron
SCL-153P
Lutron
MACL 153MH
Leviton
IPL06-10Z
Leviton
6674 - POW
Levitron
1B410S
Legrand
WS703
Legrand
DCL453PTC
1
© 2016 ON Semiconductor.
Disclaimer: ON Semiconductor is providing this design note “AS IS” and does not assume any liability arising from its use; nor
does ON Semiconductor convey any license to its or any third party’s intellectual property rights. This document is provided only to
assist customers in evaluation of the referenced circuit implementation and the recipient assumes all liability and risk associated
with its use, including, but not limited to, compliance with all regulatory standards. ON Semiconductor may change any of its
products at any time, without notice.
Design note created by Andrew Niles, Andrew Stemple, and Cody Campana.
June 2016, Rev. 1
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