NCP3065: SEPIC LED Driver for MR16

DN06033/D
Design Note – DN06033/D
NCP3065 SEPIC LED Driver for MR16
Device
Application
Input Voltage
Output Power
Topology
I/O Isolation
NCP3065
NCV3065
Solid State,
Automotive and
Marine Lighting
8-20 V,
12Vdc,
12Vac
<15 W
SEPIC
NONE
Other Specifications
Output Voltage
Current Ripple
Nominal Current
Max Current
Min Current
Output 1
Output 2
Output 3
Output 4
7.2-23 V
<15 %
0.35, 0.7, 1.0 A
1A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
Minimum Efficiency
75%
Circuit Description
This design note describes a DC-DC
converter circuit that can be easily configured
to drive LEDs at several different output
currents and voltage. It can be configured for
either AC or DC low voltage input. It is
proposed for driving High Brightness LEDs
such as Lumileds LuxeonTM, Osram OstarTM,
TopLEDTM and Golden Dragon as well as the
Cree XLAMPTM etc. and it is designed for
replace traditional MR16 bulbs with LEDs like
mentioned above. MR16 input voltage range
is usually 12 Vdc and 12Vac but you can use
this circuit for wide input voltage. You have to
only think about right component selection.
The circuit uses the NCP3065 switching
regulator configured to drive a series string of
LEDs in constant current mode.
NCP3065 is monolithic power switching
regulator capable of delivering 1.5A at output
voltages 0.235V to 35V. Circuit benefit is in
the wide input and output voltage range and
in the high efficiency and small application
volume.
The brightness of the LED or light
intensity as measured in Lumens is
proportional to the forward current flowing
through the LED. Dimming PWM input is
included.
Pulse Feedback resistor (R2) is used to
vary the slope of the oscillator ramp, achieve
duty cycle control and stabilize switching
frequency in the wide input voltage range.
October 2007, Rev. 0
This demo board can be ordered from
ON
web
site,
its
name
is
NCP3065D1SLDGEVB.
Key Features
y Buck-Boost operation
y Wide input and output operation voltage
y Regulated average output current
y Overcurrent and overvoltage protection
included
y PWM Dimming input
y High operation frequency
y Minimal input and output current ripple
y Whole application in circle with 30mm
diameter
y Designed for MR16 bulbs
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Figure 1 – Demo board top view
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DN06033/D
Schematic
Figure 2 – MR16 SEPIC converter schematic
Design Notes
A SEPIC (single-ended primary inductance converter) is distinguished by the fact that its input
voltage range can overlap the output voltage range. There is principal schema is shown in Figure
3.
Figure 3 – Principal SEPIC schematic
When switch SW is ON, energy from the input is stored in inductor L1. Capacitor CP is
connected in parallel to L2, and energy from CP is transferred to L2. The voltage across L2 is the
same as the CP voltage, which is the same as the input voltage. At this time, the diode is reverse
biased and COUT supplies output current.
If the switch SW is OFF, current in L1 flows through CP and D1 then continues to the load and
COUT. This current recharges CP for the next cycle. Current from L2 also flows through D1 to the
load and COUT that is recharging for the next cycle.
Inductors L1 and L2 could be uncoupled, but then they must be twice as large as if they are
coupled. Another advantage is that if coupled inductors are used there is very small input current
ripple.
Values of coupled inductors are set by these equations
D=
+ VF
VOUT
7,2 + 0.4
min
=
= 0,487
+ VIN
+ VF 7,2 + 8 + 0.4
VOUT
min
min
Load current 350mA:
ΔI = r ⋅ I OUT
D
0.487
= 0.8 ⋅ 0.35 ⋅
= 0.266 A
1− D
1 − 0.487
October 2007, Rev. 0
⋅D
V
8 ⋅ 0.487
=
L1, 2 = IN min
= 29 .3μH
2 ⋅ f ⋅ ΔI
2 ⋅ 250 ⋅ 10 3 ⋅ 0.266
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2
DN06033/D
Load current 700mA:
ΔI = r ⋅ I OUT
V
⋅D
8 ⋅ 0.487
L1,2 = IN min
=
= 14.6 μH
2 ⋅ f ⋅ ΔI
2 ⋅ 250 ⋅ 103 ⋅ 0.532
D
0.487
= 0.8 ⋅ 0.7 ⋅
= 0.532 A
1− D
1 − 0.487
Load current 1000mA:
ΔI = r ⋅ I OUT
⋅D
V
8 ⋅ 0.487
L1,2 = IN min
=
= 10.3μH
2 ⋅ f ⋅ ΔI
2 ⋅ 250 ⋅ 103 ⋅ 0.76
D
0.487
= 0.8 ⋅ 1 ⋅
= 0.76 A
1− D
1 − 0.487
where r is the maximum inductor current ripple factor.
The nearest coupled inductor values for the 0.7 A variant is 15 μH.
Output current is set by RS (R6, R7 and R8) value. So this resistor can be calculating by the
formula:
RS =
0,235
I OUT
.
On the evaluation board, the value of RS can be selected by jumpers J3, J4. When both are
open output current is setup to 350mA. With J3 shorted, the output current increase to 700mA and
when you shorted both J3 and J4 you setup output current to1A.
To protect the circuit against high output voltage on light loads or load disconnection, output
voltage is clamped by a Zener diode (D5) to approximately 24.5 V.
External power MOSFET is forced by internal NPN Darlington transistor, by driver from
external diode D2 and by PNP transistor Q2. Maximum MOSFET current can be calculated by this
formula:
U
max ⎛ 0,8 ⎞
23
⎛ r⎞
I Q1 max = ⎜1 + ⎟ ⋅ I OUT OUT
= ⎜1 +
= 2,5 A
⎟ ⋅ 0,7 ⋅
U IN min
2 ⎠
8
⎝ 2⎠
⎝
To minimize power MOSFET conductance losses, it is recommended to select a transistor
with small RDSON. To minimize switching losses, it is recommended to select a transistor with small
gate charge. Power MOSFET must also have a breakdown voltage higher than:
VFETPK = VIN + VOUT = 20 + 23 = 43V
Switch peak current protection is set by R1 at
I PKset =
0,2
R1
A suitable value is higher than maximum switch current.
R1 <
0,2
I Q1
max
=
0,2
= 80mΩ
2,5
Diode D1 is stressed with reverse voltage
VD1 max = VIN + VOUT = 20 + 23 = 43V
and with current
I D1 = I OUT = 0,7 A
The C1 coupling capacitor is stressed on input voltage and on current
VOUT max
23
D max =
=
= 0,74
VOUT max + VIN min 23 + 8
I C 2 RMS =
VOUT ⋅ I OUT
VIN
1 − D max 23 ⋅ 0,7 1 − 0,74
=
= 1,2 A
D max
8
0,74
and its minimal value is
C2 >
October 2007, Rev. 0
I OUT ⋅ D min
0,7 ⋅ 0,47
=
= 2μF
0,05 ⋅ V IN min ⋅ f 0,05 ⋅ 8 ⋅ 250 ⋅10 3
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DN06033/D
Application
LEDs
configuration
Vf = 7.2V
Vf = 10.8V
Vf = 14.4V
Output
current
350mA
700mA
1000mA
350mA
700mA
1000mA
350mA
700mA
1000mA
Pulse feedback resistor R2 value
Input voltage
12 Vdc
12 Vac
7.5k
5.1k
6.2k
4.3k
5.1k
5.1k
8.2k
6.8k
8.2k
5.1k
9.1k
8.2k
13k
12k
10k
10k
28k
11k
J2-3 input is used for dimming. The dimming signal level is 2-10 V or can be used TTL
compatible signal. Recommended dimming frequency is about 200 Hz. For frequencies below 100
Hz the human eye will see the flicker. The low dimming frequencies are EMI convenient. Dimming
function is based on the NCP3065’s feedback input. The second way to achieve this is to use the
IPK pin as can be seen in application note AND8298.
Conclusion
This circuit was developed based on requirements for replacing traditional MR16 bulb with
new High brightness LEDs. This circuit is ideal in applications with strings of two to six LED chips
connected in series, everywhere where input and output voltage overlap. The advantages of this
circuit include its small size, low price, wide input and output voltage ranges, and very small input
current ripple.
Figure 4 – Application example top side
October 2007, Rev. 0
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4
DN06033/D
PC Board
Figure 5 – components position on PCB
Figure 6 – PCB’s top side – not in scale
Figure 7 – PCB’s bottom side – not in scale
October 2007, Rev. 0
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5
DN06033/D
Table 1– Bill of materials
Designator
Quantity
Description
Value
Tolerance
Footprint
Manufacturer
Manufacturer
Part Number
Substitu
tion
Allowed
Lead
Free
C1
1
Ceramic capacitor SMD
47uF/25V
20%
1812
Taiyo Yuden
TMK432C476MM-T
Yes
Yes
C2, C3
2
Ceramic capacitor SMD
47uF/16V
20%
1210
Taiyo Yuden
EMK325BJ476MM-T
Yes
Yes
C4
1
Ceramic capacitor SMD
3.3nF
5%
0805
TDK
C2012C0G1H332J
Yes
Yes
C5
1
Ceramic capacitor SMD
10uF/25V
20%
1210
Taiyo Yuden
TMK325BJ106MM-TR
Yes
Yes
C6
1
Ceramic capacitor SMD
100nF
10%
0805
TDK
C2012X7R1H104K
Yes
Yes
C7
1
Ceramic capacitor SMD
100pF
5%
0805
TDK
C2012C0G1H101J
Yes
Yes
C8
1
Ceramic capacitor SMD
2.2nF
10%
0805
TDK
C2012X7R2A222K
Yes
Yes
MBRS260T3G
-
SMB
ON Semiconductor
MBRS260T3G
No
Yes
BAT54T1G
-
SOD-123
ON Semiconductor
BAT54T1G
No
Yes
MMSZ24T1G
5%
SOD-123
ON Semiconductor
MMSZ24T1G
No
Yes
Yes
D1
1
Surface Mount Schottky Power Rectifier
D2
1
Schottky Diode 30V
D5
1
J1
1
Zener Diode 500 mW 24 V
AMPMODU Mod II Right-Angle Horizontal
PCB Connector
J2
1
Input connector
J3, J4
2
Jumper, RM 2.54 mm
J3, J4
2
Q1
1
Jumper, RM 2.54 mm, PCB pin's
Power MOSFET 32Amps, 60Volts, Logic
Level, N-Channel
Q2
1
PNP General Purpose Transistor
Q3
1
General Purpose Transistor NPN
5535676-5
-
-
TYCO
5535676-5
Yes
DG350-3.50-03
-
-
Degson
DG350-3.50-03
Yes
Yes
Jumper
-
2.54
Harwin
M7686-05
Yes
Yes
Jumper - PCB pin's
-
0003
Harwin
M20-9990205
Yes
Yes
NTD32N06LT4G
-
DPAK
ON Semiconductor
NTD32N06LT4G
No
Yes
MMBT3906LT1G
-
SOT-23
ON Semiconductor
MMBT3906LT1G
No
Yes
BC817-40LT1G
-
SOT-23
ON Semiconductor
BC817-40LT1G
No
Yes
R1
1
Resistor SMD
WSL1206 -0.05R/0.5W
1%
1206
Welvyn
WSL1206 -0.05R/0.5W
Yes
Yes
R2
1
Resistor SMD
8k2
1%
0805
Vishay
CRCW08058K20FKEA
Yes
Yes
R3
1
Resistor SMD
1k5
1%
0805
Vishay
CRCW08051K50FKEA
Yes
Yes
R4
1
Resistor SMD
1k
1%
0805
Vishay
CRCW08051K00FKEA
Yes
Yes
R5
1
Resistor SMD
1k2
1%
0805
Vishay
CRCW08051K20FKEA
Yes
Yes
R6, R7, R8
3
Resistor SMD
0R68
5%
1206
Tyco Electronics
RL73K2BR68JTD
Yes
Yes
R9
1
Resistor SMD
10k
1%
0805
Vishay
CRCW080510K0FKEA
Yes
Yes
R10
1
Resistor SMD
100R
1%
0805
Vishay
CRCW0805100RFKEA
Yes
Yes
T1
1
Dual inductor
PF0553.153NL
-
-
Pulse Eng.
PF0553.153NL
Yes
Yes
IC1
1
Constant Current Switching Regulator
NCV3065MNTXG
-
DFN
ON Semiconductor
NCV3065MNTXG
No
Yes
October 2007, Rev. 0
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Comments
DN06033/D
Measurements
Figure 8 – Line regulation for VIN = 12Vdc, IOUT = 350 mA
Figure 9 – Line regulation for VIN = 12Vdc, IOUT = 700 mA
October 2007, Rev. 0
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DN06033/D
Figure 10 – Efficiency for VIN = 12Vdc, IOUT = 350mA and 700 mA
Figure 11 – Line regulation for VIN = 12Vac, IOUT = 350 mA
October 2007, Rev. 0
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DN06033/D
Figure 12 – Line regulation for VIN = 12Vac, IOUT = 700 mA
Figure 13 – Efficiency for VIN = 12Vac, IOUT = 350mA and 700 mA
October 2007, Rev. 0
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DN06033/D
Figure 14 – Dimming linearity, dimm.frequency 200Hz
1
© 2007 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 Petr Konvicny, e-mail: [email protected]
October 2007, Rev. 0
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