DN06031 -D - ON Semiconductor

DN06031/D
Design Note – DN06031/D
High Brightness LED SEPIC Driver
Device
Application
Input Voltage
Output Power
Topology
I/O Isolation
NCP3065
NCV3065
Solid State,
Automotive and
Marine Lighting
8-25 V
<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 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
70%
Circuit Description
This circuit is intended for driving high
power LEDs, such as the Cree XLAMP™
series, Lumileds Luxeon™ Rebel and K2 and
OSRAM, Golden and Platinum Dragon™ as
well as the OSTAR™. It is designed for such
wide input nominal 12 Vdc applications as
automotive and low voltage lighting (12
Vdc/12 Vac). An optional dimming PWM input
is included. The circuit is based on NCP3065
operation at 250 kHz in a non-isolated
configuration. The primary advantages of this
circuit are in the wide input voltage range,
wide output voltage range, and in its high
efficiency.
A pulse feedback resistor (R8) is used to
vary the slope of the oscillator ramp,
achieving duty cycle control and steady
switching frequency over a wide input voltage
range.
November 2007, Rev.2
Key Features
y Buck-Boost operation
y Wide input and output operation voltage
y Regulated output current
y Dimming
y High frequency operation
y Minimal input and output current ripple
y Open LED protection
y Output short circuit protection
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DN06031/D
Schematic
Figure 1 – 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. The basic schematic is shown in Figure 2.
Figure 2 – Generalized 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=
VOUT min
7.2
=
= 0.47
VOUT min + V IN min 7.2 + 8
ΔI = r ⋅ I OUT
L1, 2 =
D
0.47
= 0 .8 ⋅ 0 .7 ⋅
= 0.51A
1− D
1 − 0.47
VIN min ⋅ D
8 ⋅ 0.47
=
= 15.0μH
2 ⋅ f ⋅ ΔI
2 ⋅ 250 ⋅ 10 3 ⋅ 0.51
where r is the maximum inductor current ripple factor.
November 2007, Rev.2
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DN06031/D
For a 0.35 A output current variant of this circuit, the values of inductors are
ΔI = r ⋅ I OUT
L1, 2 =
D
0.47
= 0.95 ⋅ 0.35 ⋅
= 0.3 A
1− D
1 − 0.47
V IN min ⋅ D
8 ⋅ 0.47
=
= 25.1μH
2 ⋅ f ⋅ ΔI
2 ⋅ 250 ⋅ 10 3 ⋅ 0.3
The nearest coupled inductor value for the 0.7 A variant is 15 μH. A variant with 0.35 A output
current needs to use inductors with value 22 μH.
The output current is set by R10 (R11). So this resistor can be calculated by the formula:
R10 =
0.235
= 350mΩ .
I OUT
To protect the circuit against high output voltage under light loads or a fault condition, the
output voltage is clamped by a Zener diode (D3) to approximately 24.5 V. Capacitor C7 is used to
stabilize feedback, but it impacts line regulation. R3 fixes the line regulation error caused by C7.
External power MOSFET is driven by internal NPN Darlington transistor, external diode D2
and PNP transistor Q2. Compensated divider C3, R6 and R7 is used to reduce gate-source
voltage, mainly for high input voltage and to keep sharp edges. Maximum gate–source voltage can
be calculated by this formula:
VGS max = (V IN − VCE − V D 2 ) ⋅
R7
1500
= (27 − 1.4 − 0.4 ) ⋅
= 18.4V
R6 + R7
390 + 1500
Maximum MOSFET current can be calculated in this way:
V
max ⎛ 0.8 ⎞
23
⎛ r⎞
I Q 4 max = ⎜1 + ⎟ ⋅ I OUT OUT
= ⎜1 +
= 2.5 A
⎟ ⋅ 0.7 ⋅
VIN 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 = 18 + 23 = 41V
Cycle by cycle switch 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 maximum voltage is determined by this equation:
November 2007, Rev.2
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DN06031/D
VD1 max = VIN + VOUT = 18 + 23 = 41V
and with current
I D1 = I OUT = 0.7 A
The C4 coupling capacitor is selected based on input voltage and on current
D max =
I C 4 RMS =
VOUT max
23
=
= 0.74
VOUT max + V IN min 23 + 8
VOUT ⋅ I OUT
V IN
1 − D max 23 ⋅ 0.7 1 − 0.74
=
= 1.2 A
D max
8
0.74
and its minimal value is
C4 >
I OUT ⋅ D min
0.7 ⋅ 0.47
=
= 2 μF
0.05 ⋅ V IN min⋅ f 0.05 ⋅ 8 ⋅ 250 ⋅ 10 3
The output capacitor’s current is
I C 5 = I OUT ⋅
D max
0.74
= 0.7
= 1.2 A
1 − D max
1 − 0.74
VOUT min
7.3
⋅ I OUT ⋅ D min
⋅ 0.7 ⋅ 0.47
VIN min
8
C5 >
=
= 1.7 μF
f ⋅ r ⋅ VOUT min
250 ⋅ 10 3 ⋅ 0.1 ⋅ 7.3
The value could be much larger for higher stability, but a higher value impacts the dimming
function at low duty cycle.
The resistor R8 is used to stabilize feedback loop. Used value is compromise for whole input
and output voltage range. If this circuit is used for specified load only, it should be tuned by this
resistor to better efficiency and line regulation.
X1-3 input is used for dimming. The dimming signal level is 2-10 V. The recommended
dimming frequency is about 200 Hz. For frequencies below 100 Hz the human eye will see the
flicker. The dimming function utilizes the NCP3065’s peak current protection input. The second way
to achieve this is to use the FB pin. See figure 10.
Conclusion
This circuit is ideal in applications with strings of two to six LED chips powered from a power
supply with wide input range (8-20V). The advantages of this circuit include its small size, low price,
wide input and output voltage ranges, and very small input current ripple.
November 2007, Rev.2
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DN06031/D
PC Board
Figure 3 – components position on PCB
Figure 4 – PCB’s top side
November 2007, Rev.2
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DN06031/D
Figure 5 – PCB’s bottom side
November 2007, Rev.2
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6
R3
R9
R7
C6
C3
R2, R4, R5
C2
R8
C1
C4, C5
C7
R6
X2
X1
D2
Q1
D1
Q2
D3
IC1
Q3
R1
R10, R11
TP1, TP2, TP3, TP4, TP5, TP6
TR1
TR1
Designator
1
1
1
1
1
3
1
1
1
2
1
1
1
1
1
1
1
1
1
1
1
1
2
6
1
1
Resistor SMD
Resistor SMD
Resistor SMD
Ceramic Capacitor SMD
Ceramic Capacitor SMD
Resistor SMD
Ceramic Capacitor SMD
Resistor SMD
Ceramic Capacitor SMD
Capacitor
Ceramic Capacitor SMD
Resistor SMD
Inlet Terminal Block
Outlet Terminal Block
Schottky Diode 30V
General Purpose Transistor NPN
Surface Mount Schottky Power Rectifier
PNP General Purpose Transistor
Zener Diode 500 mW 24 V
Constant Current Switching Regulator
Power MOSFET 24 Amps, 60 Volts, Logic Level, N-Channel
Resistor SMD
Resistor SMD
Test Point
Transformer for 0.35A version
Transformer for 0.7A version
Quantity Description
1M5
1k
1k5
2n7
6n8
10k
10uF/25V
27k
100nF
120uF/50V
330pF
390R
DG350-3.50-02
DG350-3.50-03
BAT54HT1G
BC817-40LT1G
MBRS260T3G
MMBT3906LT1G
MMSZ24T1G
NCV3065MNTXG
NTD24N06LT4G
0R050
0R68
Terminal, PCB Black PK100
PF0553.223
PF0553.153
Value
Vishay
Vishay
Vishay
Murata
Kemet
Vishay
Murata
Vishay
Kemet
Koshin
Kemet
Vishay
Degson
Degson
ON Semiconductor
ON Semiconductor
ON Semiconductor
ON Semiconductor
ON Semiconductor
ON Semiconductor
ON Semiconductor
Welwyn
Tyco Electronics
Vero
Pulse
Pulse
Footprint Manufacturer
1%
0805
1%
0805
1%
0805
5%
0805
10%
0805
1%
0805
+80%/-20%
1210
1%
0805
5%
0805
20%
8x15
5%
0805
1%
0805
SOD-323
SOT-23
SMB
SOT-23
5%
SOT-123
DFN
DPAK
1%
2010
5%
1206
1.02mm
-
Tolerance
Bill of Materials for the NPC3065 SEPIC Demoboard
CRCW08051M50FKEA
CRCW08051K00FKEA
CRCW08051K50FKEA
GCM2165C1H272JA16D
C0805C682K5RAC
CRCW080510K0FKEA
GRM32NF51E106ZA01L
CRCW080527K0FKEA
C0805C104J5RAC
KZH-50V121MG4
C0805C331J5GAC-TU
CRCW0805390RFKEA
DG350-3.50-02
DG350-3.50-03
BAT54HT1G
BC817-40LT1G
MBRS260T3G
MMBT3906LT1G
MMSZ24T1G
NCV3065MNTXG
NTD24N06LT4G
LR2010-R05FW
RL73K2BR68JTD
20-2137
PF0553.223
PF0553.153
Manufacturer Part Number
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
No
No
No
No
No
No
No
Yes
Yes
Yes
No
No
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Substitution Lead
Allowed
Free
Comments
DN06031/D
November 2007, Rev.2
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DN06031/D
Measurements
NCP3065 SEPIC Converter - Line regulation, IOUT = 350 mA
0,400
0,390
0,380
0,370
IOUT [A]
0,360
0,350
0,340
0,330
0,320
0,310
0,300
8
9
10
11
12
13
14
15
6chip LED, Vf = 22V
16
17
VIN [V]
18
19
4chip LED, Vf = 14V
20
21
22
23
24
25
23
24
25
2 LEDs, Vf = 7V
Figure 6 – Line regulation for IOUT = 350 mA
NCP3065 SEPIC Converter - Efficiency, IOUT = 350mA
95
90
η [%]
85
80
75
70
65
8
9
10
11
12
13
14
15
6chip LED, Vf = 22V
16
17
VIN [V]
18
19
4chip LED, Vf = 14V
20
21
22
2 LEDs, Vf = 7V
Figure 7 – Efficiency for IOUT = 350 mA
November 2007, Rev.2
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DN06031/D
NCP3065 SEPIC Converter - Line regulation, IOUT = 700 mA
0,800
0,780
0,760
0,740
IOUT [A]
0,720
0,700
0,680
0,660
0,640
0,620
0,600
8
9
10
11
12
13
14
15
6chip LED, Vf = 22V
16
17
VIN [V]
18
19
4chip LED, Vf = 14V
20
21
22
23
24
25
23
24
25
2 LEDs, Vf = 7V
Figure 8 – Line regulation for IOUT = 700 mA
NCP3065 SEPIC Converter - Efficiency, IOUT = 700 mA
95
90
η [%]
85
80
75
70
8
9
10
11
12
13
14
15
6chip LED, Vf = 22V
16
17
VIN [V]
18
4chip LED, Vf = 14V
19
20
21
22
2 LEDs, Vf = 7V
Figure 9 – Efficiency for IOUT = 700 mA
November 2007, Rev.2
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DN06031/D
NCP3065 SEPIC Converter - Dimming Linearity
700
600
IOUT[mA]
500
400
300
200
100
0
0
10
20
30
40
50
D[%]
60
70
80
90
100
Figure 10 – Dimming linearity, dimming frequency 200Hz
Figure 11 – PCB’s top side
November 2007, Rev.2
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DN06031/D
Figure 12 – PCB’s bottom side
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 Konvičný, Tomáš Tichý, e-mail: [email protected], [email protected]
November 2007, Rev.2
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