18V 350mA 5W LED Driver Using AP3706

18V 350mA 5W LED driver using AP3706


System Engineering Department BCD Semiconductor Manufacturing Limited 12/22/2008

Summary of Report Specifications 85~264Vac, 85~264Vac, 18V/350mA Applications

LED driver 

Primary Side Regulation (PSR) solution without opto-coupler



High efficiency (>75% ) due to PFM (Pulse Frequency Modulation) operation and low startup/ operating current

Key features



±5% constant current (CC) regulation



Pass EN55022 Class B with 6dB margin without Y cap



High reliability guaranteed by built-in multi-protection functions, e.g. soft-start, OVP, OVP, OCkP (Open Circuit Protection) and SCP (Short Circuit Protection) functions

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Wide operation temperature range: -5 ~ 75℃



Small size to fit in 25mm diameter and 60mm length lamp holder



Cost effective total LED driver solution

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Contents 1. Introduction .............................................. ..................................................................... ............................................... ............................................... ............................. ...... 3 2. Specifications ............................................ ................................................................... ............................................... ............................................... ............................. ...... 5 3. Schematic ........................................... .................................................................. .............................................. .............................................. ..................................... .............. 6 4. Circuit Description ........................................... .................................................................. .............................................. ............................................. ...................... 7

4.1. AC input filters and Rectifiers: ............................................. .................................................................... ..................................... .............. 7 4.2. Power converter: ............................................ ................................................................... .............................................. ..................................... .............. 7 4.3. AP3706 related circuitry: .............................................. ..................................................................... ............................................. ...................... 7 5. BOM and transformer specifications ............................................ ................................................................... ..................................... .............. 9

5.2. Transformer specifications............................................................ specifications................................................................................... ........................... .... 10 5.2.1. Electrical Diagram............................................................... Diagram...................................................................................... ......................... 10 5.2.2. Electrical Specifications ........................................... .................................................................. ................................... ............ 10 5.2.3. Materials ............................................ ................................................................... .............................................. ....................................1 .............11 1 5.2.4. Transformer Build Diagram ............................................. .................................................................... ............................11 .....11 5.2.5. Transformer Construction.................. Construction......................................... .............................................. ....................................1 .............11 1 6. PCB layout ............................................. .................................................................... .............................................. .............................................. ............................... ........ 12 7. Electrical performance ............................................ ................................................................... .............................................. ................................... ............ 13

7.2. Output I-V and regulation................................................................ regulation....................................................................................... ......................... 13 7.3. No load input power power ............................................. ..................................................................... ............................................... ........................... .... 16 8. Thermal performance .............................................. ..................................................................... .............................................. ................................... ............ 16 9. Key Operating Waveforms ............................................. ..................................................................... ............................................... ........................... .... 17

9.2. Collector voltage of power transistor................................................... transistor....................................................................... .................... 18 9.3. Startup characterize............................ characteriz e................................................... .............................................. .............................................. ......................... 19 10. EMI test results............................ results................................................... .............................................. .............................................. ....................................... ................ 20

10.2. Radiated EMI ........................................... .................................................................. .............................................. ....................................... ................ 21 10.4 Line surge test.................... test ........................................... .............................................. .............................................. .............................................. ......................... 22 10.5 ESD test .............................................. ..................................................................... .............................................. .............................................. ............................... ........ 23 Summary of test results ........................................... .................................................................. .............................................. ....................................... ................ 24 Revision history ............................................ ................................................................... ............................................... ............................................... ........................... .... 25

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1. Introduction This report describes a 5W constant voltage/constant current universal input power supply for LED driver or similar applications. This design was based on BCD’s cost effective Primary Side Regulation (PSR) controller, AP3706. The mechanic dimensions are 55.6mm in length, 20mm in width and 20mm in height.

Figure 1. Photo of 18V/350mA LED driver demo board (Top view and bottom view) The AP3706 is an AC/DC power supply controller for the cost effective LED driver and adapter applications which can pass Energy Star EPS 2.0 and require less than 300mW no load input power. It can achieve constant voltage and constant current (CV and CC) regulation without requiring an opto-coupler and secondary control circuitry. Meanwhile, it also eliminates the need of loop compensation circuitry while maintaining the system stability. With the unique random frequency dithering technique, AP3706 system can get good EMI performance. Compared with the traditional Pulse Width Modulation control for CV and CC control technique, this device uses Pulse Frequency Modulation (PFM) technique to achieve tight CV and CC regulation, which guarantees high efficiency at light loading and makes the driver system built with AP3706 easily to pass the active mode efficiency criteria of Energy Star EPS 2.0. Designed to work in Discontinuous Current Mode (DCM), the power system using the AP3706 operates with constant primary peak current and the CV regulation is realized by modulating switching frequency. So the switching frequency presents a linear characteristic with the change of the loading. The CC regulation is implemented by a fixed ratio between the conduction time and off time of the secondary schottky rectifier. The detailed operation principle can refer to the datasheet of AP3706. The AP3706 consists of a 5V regulator, CV feedback and logic circuitry, constant peak current setting circuit, leading edge blanking circuit, optimized BJT driver circuitry, over voltage/open circuit protection (OVP/OCkP) circuitry and a PFM controller for CV and CC frequency modulation.

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With the built-in soft-start, OVP, OCkP and SCP (Short Circuit Protection) functions, the AP3706 can achieve high reliability in abnormal conditions without additional components and cost. This document contains the power supply specification, schematic, BOM (bill of materials) including transformer architecture, PCB layout and key performance features with detailed test data and waveforms.

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2. Specifications Description

Min

Typ

Max

Units

264

VAC

63

Hz

300

mW

24

V

Conditions

Input

Voltage

85

Frequency

47

50/60

No Load Input Power Output

Output Voltage

16

18

Output Ripple Voltage Output Current

200 315

Output Power (Po)

Efficiency(

EMI

Version 1.0

350 6.3

75

385

mVpp 20M bandwidth mA W

%

Measured at full load,25℃

Pass EN55022 Class B with 6dB margin

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3. Schematic

Figure 2. Schematic of 18V/350mA LED driver solution

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4. Circuit Description The power supply uses AP3706 to realize a primary side regulation flyback converter.

4.1. AC input filters and Rectifiers: The AC line voltage is rectified by diode bridge D1 to a DC bus voltage. C1, L1, L2 and C2 compose a πfilter to achieve good EMI performance in attenuating the differential mode EMI noise, in which L1 is mainly to limit EMI noise in middle frequency (less than 1Mhz) and L2 has good high frequency characteristic to eliminate EMI noise in high frequency (high than 1Mhz). And F1 is used to limit the input surge current and also work as a fuse for ultimate protection in any catastrophic failure. R18 is helpful for the system to pass surge test by generating a bypass path of L1.

4.2. Power converter: In the main power supply topology of a flyback converter, the transformer T1 is magnetized and demagnetized by on/off control of the BJT transistor Q1. Thus the DC bus voltage in the primary side is converted to AC voltage on the secondary winding of T1. A snubber circuit composed of R9, D4 and C6 is added to suppress the spike voltage across the collector of Q1 and achieve good EMI performance as well by decreasing dv/dt of Vce of Q1 and di/dt of leakage current during switching off period. By an optimized driving circuitry within the AP3706, the maximum allowable peak voltage across the collector of Q1 is Vces, which makes the use of popular BJT transistor with 400V Vceo and 700V Vces feasible. The output rectification circuitry is made up of a schottky diode D2 and electrolytic capacitors C3, C5. A dummy load R13 is used to control the output voltage in no load condition to an acceptable level. The adoption of the RC snubber composed of R5 and C12 is to suppress the voltage spike across the schottky diode D2 and thereby attenuate the radiated EMI noise.

4.3. AP3706 related circuitry: A common auxiliary winding is adopted in this schematic for both CV feedback and bias supply. CV feedback and bias supply can be separated as two windings to achieve tighter CV regulation. In the CV feedback network, R15 and R16 are required to use the resistors with 1% precision. And D3 and C4 constitute the bias supply circuitry for the AP3706. In

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order to ensure good driving effect for Q1, C4 should be placed as close as possible to Vcc pin of the AP3706. R3, R10 compose the startup resistor and 1.5M ohm is recommended for the sum of these two resistors considering the tradeoff between a reasonable startup time and guaranteed reliable startup at low AC line. The primary peak current of the flyback converter is set by the current sense resistor R2 and R4 with 1% precision. The ratio of R7 to R8 determines the line compensation to eliminate the variation of CC regulation with the line voltage.

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5. BOM and transformer specifications 5.1. BOM Item

C1, C2

Description

QTY

Electrolytic capacitor 4.7uF/400V,Φ=8mm, Rubycon

2

C3, C5

Electrolytic capacitor 220uF/25V,Φ=8mm

2

C4

Electrolytic capacitor 2.2uF/50V,Φ=4mm

1

C6

CAP 2.2n/1000V, d=5mm

1

C8

CAP 220pF 0603

1

C9

CAP 100nF 0603

1

C12

CAP 10nF 0805

1

D1

Bridge DIODE,MB6S,SOIC-4

1

D2

DIODE, EGP20F, 2A/300V, DO-201

1

DIODE, FR107,DO-41

2

F1

10Ω, 2.5 W, Fusible/Flame resistor

1

L1

Inductor, 1mH/0.3A

1

L2

Inductor, 10uH/0.3A

1

Q1

transistor NPN, APT13003EU-E1, TO126 (BCD)

1

R2

RES 1.8 ohm 1% 1206

1

R4

RES 5.1 ohm 1% 0603

1

R3

RES 510k ohm 1206

1

RES 10 ohm 1206

2

R7

RES 3k ohm 1% 0603

1

R8

RES 5.1M ohm 1% 1206

1

R9

RES 100k ohm 1206

1

R10

RES 470k ohm 1% 1206

1

R13,R15, R18

RES 5.1k ohm 1206

3

D3, D4

R5, R11

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R14

RES 180k ohm 0603

1

R16

RES 12k ohm 0603

1

T1

Transformer EE13

1

U1

AP3706, SOIC-8 (BCD)

1

Z1

24V Zener, SOD80

1

5.2. Transformer specifications 5.2.1. Electrical Diagram

Figure 3. Transformer electrical diagram

5.2.2. Electrical Specifications Primary Inductance

Pin 2-1, all other windings open, measured at 1kHz, 0.4VRMS

Primary Leakage

Pin2-1,all other windings shorted, measured at

Inductance

10kHz, 0.4VRMS

Electrical Strength

60 seconds, 60HZ, from Pin 1-5 to Pin 6-10

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1.85 mH,

5%

50uH (Max) 3000Vac

10


5.2.3. Materials Item

Description

[1]

Core:EE13, PC40 or equivalent

[2]

Bobbin: EE13, Horizontal, 8 Pin, (4/4)

[3]

Wire: ø0.19mm, for the Primary Winding

[4]

Wire: ø0.1mm, for the Auxiliary Winding

[5]

Wire: ø0.3mm for Secondary Winding

[6]

Tape: 0.05mm thick, 7.0 mm wide

[7]

Glue

5.2.4. Transformer Build Diagram

Figure 4. Transformer Build Diagram

5.2.5. Transformer Construction Bobbin Orientation

Place the bobbin on the winding machine with pins 1-4 on the right side and pins 5-8 on the left side. Start at Pin 2. Wind 30 turns of item [3] from left to right. Wind the next 30 turns

W1,

on the next layer from right to left. Wind the next 30 turns of item from left to

Primary Winding

right. Wind the next 30 turns on the next layer from right to left. Wind the last 20 turns from left to right. Finish on Pin 1. Wind tightly & spread evenly.

Insulation

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1 Layer of insulation tape [6].

11

18V 350mA 5W LED driver using AP3706 W2,

Start at Pin 3. Wind 25 turns of item [4] from left to right. Terminate on Pin 4.

Auxiliary winding

Wind tightly.

Shield

Start at Pin4.Wind 35 turns [4] from left to right. Terminate on the float.

Insulation

3 Layers of insulation tape [6].

Bobbin Reorientation Margin Tape

Place the bobbin on the winding machine with pins 5-8 on the right side and pins 1-4 on the left side. Wind 1mm margin tape on the primary side and secondary side both. Start at Pin 7. Wind 13 turns of item [5] from left to right. Wind the next 13 turns

W3, Secondary winding

from right to left. Wind the last 13 turns from left to right. Terminate on Pin 8. Wind tightly & spread evenly.

Insulation

1 Layers of insulation tape [6].

Core Assembly

Assemble Core.

Glue

Glue core & bobbin.

6. PCB layout The PCB layout rules are highlighted as follow: 1.

The loop area composed by the input capacitor, the primary winding of the transformer, power transistor Q1 and current sense resistors R10/R11 should be minimized for better EMI performance

2.

The RCD clamp snubber and output rectifier loop areas should be minimized to achieve good EMI performance

3.

The power ground and signal ground should be connected by one node.

Figure 5. Printed circuit layout Version 1.0

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7. Electrical performance 7.1. Active mode efficiency The LED driver system passes active mode average efficiency criteria of Energy Star EPS 2.0 final version. With five 350mA, 3.5V LED in series, the driver active efficiency at Vin=230V is higher than 78%.

79

77

) % ( y c75 n e i c i f f E 73

71

85

115

145

175

205

235

265

Vin(V)

Figure 6. full load Efficiency vs input voltage

7.2. Output I-V and regulation All the measurements were obtained in the following conditions: 1.

The power supply was assembled closely into a LED lamp holder case.

2.

The power supply with the case was placed into a carton, which was put into a full temperature chamber. The temperature inside the carton was monitored to keep a constant ambient temperature without the airflow for the testing.

3.

The readings of output voltage and current were recorded only after the power supply had worked for 30 minutes under no load condition.

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22

20

18 ) V16 ( t u o V

85V 115V 230V 264V

14

12

10 0

50

100

150

200

250

300

350

400

Iout(mA)

Figure 7. CV/CC Characteristic at 25 ℃

380

370

360

A m350 t u o340 I 330

320 90

120

150

180

210

240

Vin(V)

Figure 8. Line Regulation Of Output Current at 2 5℃

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380

370

360

A m350 t u o 340 I 330

320 90

120

150

180

210

240

Vin(V)

Figure 9. Line Regulation Of Output Current at 75 ℃

380

370

360

) A m350 ( t u o I 340

330

320 90

120

150

180

210

240

Vin (V)

Figure 10. Line Regulation Of Output Current at -5 ℃

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7.3. No load input power The measured no-load input power is 78mW at 115Vac and 160mW at 230Vac. 0.25

0.20

No load (Po=0W)

) W ( r e 0.15 w o P t u p 0.10 n I

0.05

0.00 85

115

145

175

205

235

265

Line Voltage (V)

Figure 11. No Load Input Power Vs. Input Voltage

8. Thermal performance The thermal performance was measured in a carton without the airflow, which was put into a 75 C chamber, and after the power supply had worked for 1 hour under full load condition. Two thermocouples were attached to the case of U1，D1 and Q1 firmly. Table 4. Thermal performance of key components Item

85Vac

U1 (AP3703)

110 C

Q1 (13002)

116 C

T1

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o

o

o

111 C

115Vac o

105 C o

118 C o

110 C

230Vac o

100 C o

105 C o

109 C

264Vac o

100 C o

105 C o

109 C

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9. Key Operating Waveforms 9.1. Output ripple voltage All measurements were made with an oscilloscope with 20 MHz bandwidth.

Figure 12. Ripple, Vin=85Vac, Full Load, 10us, 200mV/div, peak-peak: 412mV

Figure 13. Ripple, Vin=265Vac, Full Load, 10us, 200mV/div, peak-peak: 384mV

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9.2. Collector voltage of power transistor

Figure 14. Collector voltage, Vin=85Vac, full load. 100V, 20us/div.

Figure 15. Collector voltage, Vin=265Vac, full load. 100V, 20us/div.

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9.3. Startup characterize

Figure 16. Rise time, 115Vac, Full Load, 4ms/div

Figure 17. Rise time, 230Vac, Full Load, 4ms/div o

The driver can start at -10 C and 85V ac input voltage.

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10. EMI test results 10.1. Conducted EMI Measured with charger output grounding, >6dB margin to EN55022 class B with QP detector and >6dB margin EN55022 class B with Average detector.

Att 10 dB dBµV

RBW

9 kHz

MT

1 s

PREAMP OFF

1 MHz

80

Att 10 dB dBµV

10 MHz

9 kHz

MT

1 s

PREAMP OFF

1 MHz

80

70

RBW

10 MHz

70

SGL 1 PK

CLRWR

EN55022Q

CLRWR

60

EN55022A

2 AV

SGL 1 PK

EN55022Q

CLRWR

EN55022A

2 AV TDF

50

40

60

CLRWR

TDF 50

40

30

30

6DB

6DB

20

20

10

10

0

0

-10

-10

-20

-20

150 kHz

30 MHz

Date: 22.DEC.2008

08:37:48

150 kHz

30 MHz

Date: 22.DEC.2008

08:32:01

EDIT PEAK LIST (Final Measurement Results)

EDIT PEAK LIST (Final Measurement Results)

Trace1:

EN55022Q

Trace1:

EN55022Q

Trace2:

EN55022A

Trace2:

EN55022A

Trace3:

---

Trace3:

TRACE

FREQUENCY

LEVEL dBµV

2

Average

354 kHz

36.51

1

Quasi Peak

358 kHz

34.17

1

Quasi Peak

838 kHz

43.60

2

Average

838 kHz

36.78

1

Quasi Peak

1.63 MHz

2

Average

1.63 MHz

1

Quasi Peak

2.47 MHz

2

Average

3.57 MHz

1

Quasi Peak

5.554 MHz

2

Average

1

Quasi Peak

2

Average

18.686 MHz

DELTA LIMIT dB -12.35

--FREQUENCY

LEVEL dBµV

Average

810 kHz

-24.60

2

Average

1.378 MHz

36.92

-9.07

-12.39

1

Quasi Peak

810 kHz

44.57

-11.42

-9.21

2

Average

306 kHz

38.63

-11.44

47.55

-8.44

2

Average

4.874 MHz

33.16

-12.83

39.85

-6.14

2

Average

24.066 MHz

36.03

-13.96

46.09

-9.90

1

Quasi Peak

1.77 MHz

41.93

-14.06

37.98

-8.01

1

Quasi Peak

358 kHz

43.66

-15.10

43.31

-16.68

2

Average

10.034 MHz

33.38

-16.61

5.554 MHz

32.58

-17.41

1

Quasi Peak

3.346 MHz

38.62

-17.37

18.382 MHz

39.14

-20.85

1

Quasi Peak

8.37 MHz

41.51

-18.49

30.41

-19.58

1

Quasi Peak

16.886 MHz

26.34

-33.65

230VAC/50Hz, full load, Neutral

38.75

DELTA LIMIT dB

2

Figure 18. Conducted EMI,

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TRACE

-7.24

Figure 19. Conducted EMI, 230VAC/50Hz, full load, Line

20


10.2. Radiated EMI Measure radiated EMI with >6dB margin to EN55022 Class B with QP detector.

Figure 20. Radiated EMI, 230VAC/50Hz, full load, Vertical

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Figure 21. Radiated EMI, 230VAC/50Hz, full load, Horizontal

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5V/890mA Battery Charger Solution Using AP3703

10.3 Line surge test The surge test follows IEC61000-4-5 using input line surge (1.2us/50us).

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10.4 ESD test The ESD test follows IEC61000-4-2.

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Summary of test results Description

Min

Typ

Max

Units

Tested results

264

VAC

63

Hz

300

mW

78mW at 115Vac and 160mW at 230Vac

19

V

Pass

500

mVpp

Pass

367.5

mA

Pass

W

Pass

%

79% at 230Vac

Input

Voltage

85

Frequency

47

50/60

No Load Input Power

Output

Output Voltage

16

18

Output Ripple Voltage Output Current

332.5

Output Power (Pno)

350 6.3

Efficiency(

75

EMI

Pass EN55022 Class B with 6dB margin

Pass

Surge

IEC61000-4-5, Pass 2KV

Pass

ESD

IEC61000-4-2, Pass 8KV

Pass

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Revision history Versions

Date

Author

Description for changes

Reviewed

Version 1.0

12/22/2008

Jian Sun/Simon Zhu

Initial release

Charles Sun

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18V 350mA 5W LED Driver Using AP3706

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