ST AN2753 Application note

AN2753

Application note

6 W single-output VIPer17 demonstration board

Introduction

The new VIPer17 device integrates in the same package two components: an advanced PWM controller with built-in BCD6 technology and an 800 V avalanche rugged vertical power MOSFET. The device is suitable for offline power conversion operating either with wide range input voltage (85 VAC - 270 VAC) up to 6 W or with single range input voltage (85 VAC - 132 VAC or 175 VAC - 265 VAC). With European range input voltage (175 VAC - 265 VAC) the device can handle up to 10 W of output power. The proposed solution has the advantage of using few external components compared to a discrete solution, providing several switch mode power supply protections and very low standby consumption in no-load condition. The device operates at fixed frequency that can be 115 kHz or 60 kHz. Frequency jittering is implemented which helps to meet the standards regarding electromagnetic disturbance. The protections present on the device such as overload and output overvoltage protections, secondary winding short-circuit protection, hard transformer saturation and brownout protections improve the reliability and safety of the design. Moreover internal thermal shutdown and an 800 V avalanche rugged power MOSFET improve the robustness of the system.

The VIPer17 demonstration board is a standard single-output isolated flyback converter that uses all the protections mentioned above. If brownout and overvoltage protection are not necessary, the number of external components is further reduced.

Figure 1. VIPer17HN demonstration board

Note:

VIPer17HN is the full order code.

October 2009

Doc ID 14654 Rev 2

1/31

www.st.com

Contents	AN2753

Contents

1	Board description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		. 5
	1.1	Transformer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	8
2	Testing the board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		9
	2.1	Typical board waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	9
3	Precision of the regulation and output voltage ripple . . . . . . . . . . . . .		11

3.1 Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 3.2 Light-load performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 3.3 Soft-start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 3.4 Overload protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 3.5 Secondary winding short-circuit protection . . . . . . . . . . . . . . . . . . . . . . . 20 3.6 Output overvoltage protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 3.7 Brownout protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 3.8 EMI measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

4	Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	28
5	References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	29
6	Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	30

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AN2753	List of tables

List of tables

Table 1. Electrical specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Table 2. Bill of materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Table 3. Transformer characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Table 4. Output voltage and VDD line-load regulation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Table 5. High frequency output voltage ripple . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Table 6. Burst mode related output voltage ripple . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Table 7. Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Table 8. Active mode efficiencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Table 9. Line voltage averaged efficiency vs. load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Table 10. ENERGY STAR® recommended active mode efficiency vs. Pno [1]. . . . . . . . . . . . . . . . . 17 Table 11. No-load input power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Table 12. Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

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List of figures	AN2753

List of figures

Figure 1. VIPer17HN demonstration board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Figure 2. Schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Figure 3. Bottom view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Figure 4. Side view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Figure 5. Pins distances. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Figure 6. Electrical diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Figure 7. Drain current and voltage at full load and nominal input voltages (115 VAC) . . . . . . . . . . . . 9 Figure 8. Drain current and voltage at full load and nominal input voltages (230 VAC) . . . . . . . . . . . . 9 Figure 9. Drain current and voltage at full load and minimum input voltage (90 VAC) . . . . . . . . . . . . 9 Figure 10. Drain current and voltage at full load and maximum input voltages (265 VAC). . . . . . . . . . . 9 Figure 11. Frequency jittering (115 VIN_AC, full load) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Figure 12. Output voltage ripple 115 VIN_AC full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Figure 13. Output voltage ripple 115 VIN_AC full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Figure 14. Output voltage ripple 115 VIN_AC no load (burst mode) . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Figure 15. Output voltage ripple 230 VIN_AC no load (burst mode) . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Figure 16. Efficiency vs. VIN. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Figure 17. Efficiency vs. load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Figure 18. Active mode efficiency vs. VIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Figure 19. VIN Average efficiency vs. load. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Figure 20. Soft-start feature waveforms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Figure 21. Output short-circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Figure 22. Operation with output shorted. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Figure 23. 2nd OCP protection tripping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Figure 24. Operating with secondary winding shorted. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Figure 25. OVP circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Figure 26. OVP protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Figure 27. OVP protection (detail) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Figure 28. Jumper J3 setting for brownout protection - brownout disabled . . . . . . . . . . . . . . . . . . . . . 24 Figure 29. Jumper J3 setting for brownout protection - brownout enabled . . . . . . . . . . . . . . . . . . . . . 24 Figure 30. Brownout protection block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Figure 31. Brownout protection tripping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Figure 32. Operating with brownout protection activated. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Figure 33. Restart after brownout protection activated (detail) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Figure 34. Restart after brownout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Figure 35. 115 VAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Figure 36. 230 VAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

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AN2753	Board description

1 Board description

The electrical specifications of the VIPer17 demonstration board are listed in the table below.

Table 1.	Electrical specification
	Parameter	Symbol	Value

	Input voltage range	VIN	90 VRMS; 265 VRMS
	Output voltage	VOUT	12 V
	Max output current	IOUT	500 mA
Precision of output regulation		VOUT_LF	±5%

High frequency output voltage ripple		VOUT_HF	50 mV

The schematics and bill of material of the board are shown in Figure 2 and Table 2 respectively and the transformer description is given in Table 3.

In order to minimize magnetic component size, the higher operating frequency device (VIPer17) in the DIP7 package was selected. The average switching frequency (fSW_avg) is 115 kHz (typ.). The switching frequency is modulated by a triangular waveform at 250 Hz

between fSWavg = fm and where fm is 8 kHz (typ.). This frequency modulation

(frequency jittering) spreads the spectrum of the electromagnetic interference generated by the switching of the MOSFET, reducing its maximum value and facilitating compliance with EMI standards.

In order to obtain good precision in the output regulation, a secondary regulation scheme was used, monitoring directly the output voltage.

Thanks to the adjustable primary current limitation it is possible to fix the maximum power that the converter can deliver to the output. The overload protection offers a good degree of safety under output short-circuit or overload condition. As the protection is tripped the system operates in hiccup mode reducing the power throughput to a few hundreds of milliwatts. A second level of current limitation that latches the device if exceeded ensures safety also in case of output diode failure (short) or secondary winding short-circuit. Output overvoltage protection and brownout protection are also implemented. By simply changing the position of a jumper in the board it is possible to disable the brownout protection if it is not necessary in the specific application.

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Board

Figure

description

10uF 450V

P6KE250

D5 STTH1L06 D3

10uF 450V

N.M

STPS2H100

10uH

12V 500mA

Schematic

BR1

C10

ZL 470uF 25V

ZLG 47uF 25V

CON2

TRANSFORMER

1600k

1N4148

BAT46

Y1 1.8nF

ID Doc

NTC1

R14

Rev 14654

R13

10 Ohm NTC

180k

1600k

VIPER17HN

OPTO1

VDD

DRAIN

PC817

BROWN OUT

500mA FUSE

JUMPER

CONTROL

15k 1%

CONT

C11

C12

SOURCE

33nF

R10

22uF 25V

10nF

VR1

82k

1 2

22k

33nF

TL431

CON2

47k

3.3nF

R12

3.9k 1%

10k

AN2753

AN2753					Board description

	Table 2.	Bill of materials

	Item		Quantity	Reference	Part

	1		1	BR1	Bridge

	2		1	C1	EPCOS X2 100 nF MKP B32922

	3		2	C2,C3	Rubycon YXA 10 µF 450 V

	4		1	C4	22 µF 25 V

	5		1	C5	47 pF 630 V (not mounted)

	6		1	C6	3.3 nF

	7		2	C7,C11	33 nF

	8		1	C8	Y1 1.8 nF

	9		1	C9	Rubycon ZL 470 µF 25 V

	10		1	C10	Rubycon ZLG 47 µF 25V

	11		1	C12	10 nF

	12		1	D1	BAT46

	13		1	D2	1N4148

	14		1	D3	STTH1L06

	15		1	D4	STPS2H100

	16		1	D5	P6KE250

	17		1	F1	500 mA fuse

	20		1	L1	10 µH

	21		1	NTC1	EPCOS B57153S0100M 10 Ω NTC

	22		1	OPTO1	PC817

	23		1	R1	10

	24		2	R2,R4	1500 kΩ

	25		1	R3	47 kΩ

	26		1	R5	18 kΩ

	27		2	R6,R13	1 kΩ

	28		1	R8	15 kΩ 1%

	29		1	R9	3.9 kΩ 1%

	30		1	R10	82 kΩ

	31		1	R12	10 kΩ

	32		1	R14	180 kΩ

	33		1	T1	Transformer

	34		1	T2	Coilcraft BU9-10325BL

	35		1	U1	VIPer17

	36		1	VR1	TL431

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Board description	AN2753

1.1Transformer

Transformer characteristics are listed in the table below.

Table 3.	Transformer characteristics
	Item name	Value	Measure condition

	Manufacturer	Magnetica

	Part number	1335.0034 Rev01

Primary inductance		1.2 mH +/- 15%	Fr = 1 kHz, Ta = 20 °C

Leakage primary inductance		3.2% of primary	Pins 1 & 2 shorted, pins 7 & 8 shorted
Leakage primary inductance		3.2% of primary	Fr=10 kHz, Ta = 20 °C
			Fr=10 kHz, Ta = 20 °C

Primary to secondary turn ratio		7.85 ± 5%	Fr = 10 kHz Ta = 20 °C

Primary to auxiliary turn ratio		7.85 ± 5%	Fr = 10 kHz Ta = 20 °C

	Insulation	4 kV	Primary to secondary

Figure 3, 4, 5, 6 show size (mm), pin connection and pins distances (mm) of the transformer.

Figure 3. Bottom view	Figure 4. Side view

Figure 5. Pins distances	Figure 6.	Electrical diagram
	5
		A
		7
	4	C
	4
	1	8
		B
	2

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AN2753	Testing the board

2 Testing the board

2.1Typical board waveforms

The board operates with wide range input voltages and the relevant waveforms are shown with the minimum, maximum and nominal input voltages.

Figure 7 and Figure 8 show the drain current and the drain voltage waveforms at the nominal input voltages, that are 115 VAC and 230 VAC when the load is the maximum

(500 mA). Figure 9 and Figure 10 show the same waveforms for the same load condition, but the input voltages are the minimum (90 VAC) and the maximum (265 VAC).

Figure 7. Drain current and voltage at full	Figure 8. Drain current and voltage at full
load and nominal input voltages	load and nominal input voltages
(115 VAC)	(230 VAC)

Figure 9. Drain current and voltage at full load and minimum input voltage (90 VAC)

Figure 10. Drain current and voltage at full load and maximum input voltages (265 VAC)

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Testing the board	AN2753

Figure 11 shows the drain current and the voltage on the feedback pin in a time interval of about 10 ms. The system is working with a constant load but the voltage on the feedback pin is a triangular wave shape as well as the peak drain current. These changes are the result of the frequency jittering.

In a fixed frequency flyback converter, operating in discontinuous conduction mode, the output power is proportional to the switching frequency according to the following formula:

Equation 1

P		=	1	L		I	2		η
	OUT		--		P		PK f	SW
			2

where LP is the transformer primary inductance, IPK is the drain peak current and η is the converter's efficiency. The VIPer17 internal oscillator gives a switching frequency modulated by a triangular waveform of 250 Hz (typ.). The power demand of the load is constant, but, due to the variable switching frequency, the power delivered is not constant if IPK is constant. The control loop reacts to the unsteady switching frequency, modulating the feedback pin voltage and then, the drain peak current.

Figure 11. Frequency jittering (115 VIN_AC, full load)

CH2: VFB 200 mV/Div (Light blue)

CH4: IDRAIN 50 mA/Div (Green)

Time: 1 ms/Div

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