Reference Design Report for a 21W (42V/0.5A) LED Driver...

©SiFirst Technology - 1 - SiFirst_RDR_SFL900_V1.0

21W LED Driver Using SFL900 SFL900_LED Driver_21W_42V0.5A_V1.0

Reference Design Report for a 21W (42V/0.5A)

LED Driver Using SFL900

Specification 90-264VAC Input; 42V/0.5A output

Application LED Driver

Author System Engineering Department

Document Number

SFL900_LED Driver_21W_42V0.5A

Date 2012 06

Revision 1.0

Key Features

◆ Both Primary-side control and secondary-side control with single stage PFC for LED driver

◆ Power factor >0.9 ◆ Built in Soft Start ◆ THD



Contents 1. Introduction ................................................................................................................................ 3

2. Specifiction ................................................................................................................................. 3

3. Schematic .................................................................................................................................... 4

4. PCB Layout ................................................................................................................................. 4

5. Module Snapshot .................................................................................................................... 6

6. Bill of Materials ......................................................................................................................... 7

7. Transformer Specifications ............................................................................................... 8

7.1 Electrical Diagram ...................................................................................................................... 8

7.2 Electrical Specification .............................................................................................................. 8

7.3 Materials ......................................................................................................................................... 8

7.4 Transformer Build Diagram ..................................................................................................... 9

7.5 Tranformer Winding Specification .......................................................................................... 9

8. Performance Data ................................................................................................................. 10

8.1 Test Equipments ...................................................................................................................... 10

8.2 Summary of Testing Results ................................................................................................. 10

8.3 PF/THD/Efficiency vs. Power and Line Voltage ............................................................... 11

8.4 No Load Input Power ............................................................................................................... 12

8.5 Output short Input Power ....................................................................................................... 12

9. Waveforms and Testing Results .................................................................................. 13

9.1 Drain Voltage and Current Sense waveform @ Startup .............................................. 13

9.2 Drain Voltage and Current Sense waveform @ Nomal Operation ............................ 13

9.3 Ripple and Noise ....................................................................................................................... 15

9.4 Output current overshoot ........................................................................................................ 16

9.5 Max Mosfet Vds and second diode Vak Voltage ............................................................ 16

10. Protections ............................................................................................................................. 17

10.1 Output Short Circuit Protection .......................................................................................... 17

10.2 Over Voltage Protection ........................................................................................................ 18

11. EMI Testing Results .......................................................................................................... 19

11.1 Conduction EMI Testing Results ....................................................................................... 19

11.2 Radiation EMI Testing Results ........................................................................................... 20



1. Introduction

This engineering report describes a 21W (42V/0.5A) universal input power supply for LED

Driver applications. This reference design is based on the SiFirst’s product SFL900. The

mechanic dimensions are 79mm in length, 46 mm in max width. It can be using to par 38

LED lamp.

SFL900 is a high performance, high power factor flyback PWM controller special for LED

lighting applications. The IC adopts unique super-PFC/PSRTM which can support both PSR

and SSR applications.

SFL900 has built-in load CC compensation and AC line CC compensation function, which

can further increase LED output CC accuracy. The IC has Max.90KHz frequency clamping

function and soft totem pole gate driver to improve system conduction and radiation EMI. The

IC will clear External EA Feedback network before IC power on, which can reduces startup

LED current spike. The IC also has soft start control during power on period.

2. Specifiction

Description Min Typ Max Units Remark Input

Voltage 90 115/230 264 VAC 2 Wire

Frequency 47 50/60 63 Hz

Output (Measure at the end of Cable)

Output Current 0.5 A

Output Ripple Current 150 mA

Output Current A

Line Regulation ±2 %

Load Regulation ±3 %

Continuous Output Power 21 W

Efficiency(Measure at the end of Cable)

Required average efficiency 88 % 115VAC/230VAC

Protection Feature

Short Circuit Protection Over Voltage Protection

Output shut down with automatic recovery

Environmental, Surge and ESD

Ambient Temperature 0 40 ℃

Operating Humidity 20 90 % R.H Storage Temperature -40 60 ℃

Storage Humidity 0 95 % R.H

EMI Test Pass EN55015 Class B and FCC Part15 Class B with 6dB margin



3. Schematic

4. PCB Layout

Print circuit board (PCB) layout and design are very important for switching power supply where the

voltage and current change with high dv/dt and di/dt. Good PCB layout minimizes excessive EMI and

prevents the power supply from being disrupted during surge/ESD tests. The PCB layout guidelines

are highlighted as following:

1. The area enclosed by the transformer auxiliary winding, Ddd and Cdd should be kept short path.

2. The ground of the control circuits should be connected first, then to the other circuitry.

3. Regarding the ESD discharge path, put in the shortcut pad between AC line and DC output (which

is the best way). The other method is to discharge the ESD energy to AC line through the primary

main ground. Because ESD energy is delivered from secondary to primary through the transformer

stray capacitor, the controller circuit should not be placed on the discharge path.

4. For the surge path, select fusible resistor type with wire wound type to reduce inrush current and

surge energy, using π input filter (two bulk capacitor and one inductance) to share the surge energy.

5. The drain trace length should be minimized to reduce EMI.

6. RCD Clamp and output rectifier diode loop areas should be minimized to reduce EMI

7. The AC input is located away from switching nodes to minimize noise coupling that may bypass

input filtering.



PCB Layout (Top view)

PCB

Layout (Assembly Drawing, Bottom view)



PCB Layout (Bottom Copper, Bottom view)

5. Module Snapshot



6. Bill of Materials

POSITION DESCRIPTION QTY

C1 Capacintor metal poly 154/630V, ±20% 1

C2 Capacintor Electrolytic 4.7UF/400V,8*12, ± 20% 1

C3 Capacintor Electrolytic 47UF/50V,6.3*11, ± 20% 1

C4 Capacintor Ceramic 102/1KV, ±20% 1

C5 C6 Capacintor Electrolytic 470UF/50V,10*20, ± 20% 2

C7 Capacintor Ceramic 101/50V, 0805, 10% 1




C11 Capacintor Ceramic 10PF/50V, 0805, 10% 1

C12,C13,C14 NC

CX1 Capacintor X2 0.1UF/275V P=10 1

CX2 Capacintor X2 0.047UF/275V P=10 1

LJ1 Jumper 0.6*18mm 1

R1 Resistor 10K 1206 5% 1

R3，R4 Resistor 470K 1206 5% 2


R6/R7 Resistor 3.9R 1206 1% 2

R8 Resistor 3.0R 1206 1% 1


R10，R18 Resistor 15K 0805 5% 2

R11,R26,R27 Resistor 100R 1206 5% 3

R12 Resistor 82R 1206 5% 1

R13 ,R14 Resistor 47K 1206 5% 2

R15 Resistor 100K 1206 5% 1

R16,R17 Resistor 300K 1206 5% 2

R19,R20 NC

R21 Resistor 0R 1206 5% 1

R22 Resistor 91K 0805 5% 1

R23,R24 Resistor 1M 1206 5% 2

R25 Resistor 30K 1206 5% 1

D1 Diode IN4007 1A/1KV DO-41 1

D2 Diode FR107 1A/1KV DO-41 1

D3 Diode HER304 3A/300V DO-201AD 1

D4 Diode M7 1A1KV SMA 1

D5 Diode 1N4148W SOD-123 1

BR1 Bridge B6S 0.8A/600V TO269AA 1

F1 Fuse, 2A/250V 4*10 1

L1 DR6*8 400UH 0.20mm 1

L2 DR8*10 1.5mH 0.25mm 1

LF1 UU9.8 15 mH min 1

LF2 Core T10*4*5 100UH min 0.6mm 1

T1 RM8 1.5mH 1K/1V 1

Q1 MOSFET, TK5N60 5A/600V TO-220 1

CY1 Capacintor 102/400V 1

IC1 SFL900, SO-8 1

VAR1 NC

PCB SFL9X0.PCB 1.6mm 1

app:ds:bridge



7. Transformer Specifications

7.1 Electrical Diagram

7.2 Electrical Specifications

Primary Inductance Pin 12-10, all other windings open, measured at 1KHz, 1Vrms

1.5mH, ±8%

Primary Leakage Inductance

Pin 12-10, with Pins P1-P2 shorted, measured at 10KHz, 1Vrms

20uH(max)

Electrical Strength 60 seconds, 60Hz, from N1，N2，N4，N5 to N3 3750Vac

7.3 Materials

Item Description

[1] Core: RM8, TDK PC40 or equivalent

[2] Bobbin: R8, Horizontal, 12 pins (6/6). See attached drawing

[3] Magnet Wire: Φ0.28mm, for the Shield Winding

[4] Magnet Wire: Φ0.28mm, for the Primary Winding

[5] Magnet Wire: Φ0.28mm, for the Auxiliary Winding

[6] Triple Insulated Wire: Φ0.40mm, for the Secondary Winding

[7] Tape: 0.05mm thick, 9mm wide

[8] Tube ：Φ0.70mm Teflon Tube



7.4 Transformer Build Diagram

7.5 Transformer Winding Specification

No Winding Material Start Turns Finish

1 N1 0.28mm*1 2UEW 10 28 NC

2 TAPE TAPE W=9mm 2

3 N2 0.28mm*1 2UEW 12 55 11

4 TAPE TAPE W=9mm 2

5 N3 0.40mm*1 triple insulated wire P1 27 P2

6 TAPE TAPE W=9mm 2

7 N4 0.28mm*1 2UEW 11 27 10

8 TAPE TAPE W=9mm 2

9 N5 0.28mm*1 2UEW 3 12 1

10 TAPE TAPE W=9mm 3



8. Performance Data

8.1 Test Equipments

Item Vender Vender

AC Source Gwinstek APS9501

Electrical Load Prodigit 3314F

Digital Power Meter Voltech PM1000

Oscilloscope LeCroy Wavesufer24Xs

Thermal Agilent 34970A

8.2 Summary of Testing Results

Description Test Results Units Remark Input

MAX Total Harmonic Distortion @90~264VAC

9.05 %



8.3 SFL900 PF/THD/Efficiency vs. Power and Line Voltage

Vin (VAC)

Pin (W)

Vout (V)

Iout (A)

Pout (W)

PF THD (%)

Efficiency Average

Efficiency load

regulation

90

17.50 30 0.506 15.17 0.993 6.71 86.69%

86.03% ±1.3%

20.45 35 0.503 17.65 0.994 6.90 86.31%

24.41 42 0.498 20.94 0.993 7.65 85.78%

25.87 45 0.493 22.08 0.993 8.02 85.35%

115

16.82 30 0.494 14.87 0.992 7.02 88.41%

88.30% ±1.3%

19.33 35 0.490 17.09 0.993 6.74 88.41%

23.04 42 0.484 20.33 0.994 6.38 88.24%

24.63 45 0.481 21.71 0.995 6.58 88.14%

180

16.68 30 0.496 14.87 0.982 8.33 89.15%

89.40% ±1.7%

19.17 35 0.490 17.14 0.987 6.18 89.41%

22.61 42 0.483 20.24 0.992 5.03 89.52%

24.08 45 0.479 21.56 0.993 4.81 89.53%

230

17.10 30 0.502 15.19 0.960 8.48 88.83%

89.34% ±1.8%

19.39 35 0.496 17.30 0.967 6.74 89.22%

22.96 42 0.487 20.58 0.976 4.82 89.63%

24.25 45 0.484 21.75 0.978 4.38 89.69%

264

17.24 30 0.506 15.17 0.939 9.05 87.99%

88.73% ±1.9%

19.74 35 0.499 17.49 0.951 7.05 88.60%

23.07 42 0.490 20.56 0.963 5.36 89.12%

24.54 45 0.487 21.89 0.966 4.89 89.20%

line regulation

Vout=30v Vout=35v Vout=42v Vout=45v Total regulation

±1.2% ±1.3% ±1.5% ±1.4% ±2.7%

app:ds:loadapp:ds:regulationapp:ds:regulationapp:ds:regulation



Efficiency VS Voltage

83.00%

84.00%

85.00%

86.00%

87.00%

88.00%

89.00%

90.00%

91.00%

90 115 180 230 264

Input Voltage

Efficiency 30V

35V

42V

45V

Fig.1 Efficiency vs. Line Voltage and Output Voltage

8.4 No Load Input Power

Input Voltage 90VAC 115VAC 230VAC 264VAC

SFL900 182mW 213mW 311mW 371mW

8.5 Output short Input Power

Input Voltage 90VAC 115VAC 230VAC 264VAC

SFL900 71.3mW 123.2mW 255.8mW 315.9mW



9. Waveforms and Testing Results

9.1 Drain Voltage and Current Sense waveform @ Startup

--（Red—Vcomp，Blue—Vout，Yellow—Vcs，Green—Vds）

Fig.2 Startup 90VAC, 42V load Fig.3 Startup 115VAC 42V load

Fig.4 Startup 230VAC, 42V load Fig.5 Startup 264VAC 42V load

9.2 Drain Voltage and Current Sense waveform @ Nomal Operation

--（Red—Vcomp，Blue—Iout，Yellow—Vcs，Green—Vds）

Fig.6 90VAC, 42V load Fig. 7 90VAC 42V load



Fig.8 115VAC, 42V load Fig.9 115VAC, 42V load





9.3 Ripple and Noise

Input Voltage Ripple & Noise

Waveform Ripple current Ripple Voltage

90VAC/60Hz 116mA 3.8V Fig.14

115VAC/60Hz 108mA 3.5V Fig.15

230VAC/50Hz 118mA 3.8V Fig.16

264VAC/50Hz 124mA 3.8V Fig.17

Note: Ripple and noise are measured at cable end with a 0.1uF/50V ceramic cap connected in

parallel with a 47uF/50V aluminum electrolytic cap. The oscilloscope bandwidth is limited to 20MHz.

Fig.14 Ripple & Noise @90VAC/60Hz, 42V load Fig.15 Ripple & Noise @ 115VAC/60Hz, 42V load

(Blue—Iout，Red—Vout) (Blue—Iout，Red—Vout)

Fig.16 Ripple & Noise @230VAC/50Hz, 42V load Fig.17 Ripple & Noise @ 264VAC/50Hz, 42V load

(Blue—Iout，Red—Vout) (Blue—Iout，Red—Vout)



9.4 Output current overshoot

Input Voltage Measure Data (%) SPEC Waveform

90VAC/60Hz 0



Fig.22 Output short 264VAC, 42V load Fig.23 Output short 264VAC, 42V load

10. Protections

10.1 Output Short Circuit Protection

--（Red—Vcomp，Blue—Vcc，Yellow—Vcs，Green—Vds）

Fig.24 output short 90VAC, 42V load Fig.25 output short 90VAC 42V load

Fig.26 output short 264VAC, 42V load Fig.27 output short 264VAC 42V load



10.2 Over Voltage Protection

-- Blue—Vout，Yellow—Vdem

Input Voltage Vout (V) Vdem (V) Waveform

90VAC/60Hz 48.8 3.38 Fig.28

264VAC/50Hz 49.0 3.40 Fig.30

Fig.28 90VAC no load Fig.29 90VAC no load

Fig.30 264VAC no load Fig.31 264VAC no load



11. EMI Testing Results

11.1 Conduction EMI Test

EN55015 @ Full Load Report

VIN=230V/50Hz, Line (Blue—QP yellow--AV ) VIN=230V/50Hz, Neutral (Blue—QP yellow--AV )

FCC 15 Class B @ Full Load Report

VIN=120V/60Hz, Line (QP ) VIN=120V/60Hz, Line (AV )

app:ds:yellowapp:ds:yellow



VIN=120V/60Hz, Neutral (QP ) VIN=120V/60Hz, Neutral (AV )

11.2 Radiation EMI Test

Radiation EN55022 CLASS B @ full load report

VIN=230V/50Hz, Vertical VIN=230V/50Hz, Horizontal



Radiation FCC 15 CLASS B @ full load report

VIN=120V/60Hz, Vertical VIN=120V/60Hz, Horizontal

IMPORTANT NOTICE SiFirst Technology Nanhai, Ltd (SiFirst) reserves the right to make corrections, modifications, enhancements, improvements and other changes to its products and services at any time and to discontinue any product or service without notice. Customers should obtain the latest relevant information before placing orders and should verify that such information is current and complete.

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Reference Design Report for a 21W (42V/0.5A) LED Driver...

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