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 V
(85 V
265 V
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.

- 132 VAC or 175 VAC - 265 VAC). With European range input voltage (175 VAC -

AC

) the device can handle up to 10 W of output power. The proposed solution has the

AC

- 270 VAC) up to 6 W or with single range input voltage

AC

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

2/31 Doc ID 14654 Rev 2

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 V

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

Table 11. No-load input power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Table 12. Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

®

line-load regulation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

DD

recommended active mode efficiency vs. Pno [1]. . . . . . . . . . . . . . . . . 17

Doc ID 14654 Rev 2 3/31

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 V
Figure 8. Drain current and voltage at full load and nominal input voltages (230 V
Figure 9. Drain current and voltage at full load and minimum input voltage (90 V
Figure 10. Drain current and voltage at full load and maximum input voltages (265 V

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. V

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

IN

Figure 17. Efficiency vs. load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Figure 18. Active mode efficiency vs. V
Figure 19. V

Average efficiency vs. load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

IN

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

IN

Figure 20. Soft-start feature waveforms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

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

Figure 22. Operation with output shorted. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Figure 23. 2

nd

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 V
Figure 36. 230 V

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

AC

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

AC

) . . . . . . . . . . . . 9

AC

) . . . . . . . . . . . . 9

AC

) . . . . . . . . . . . . 9

AC

). . . . . . . . . . . 9

AC

4/31 Doc ID 14654 Rev 2

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 V

Output voltage V

Max output current I

Precision of output regulation Δ

High frequency output voltage ripple Δ

IN

OUT

OUT

VOUT_LF

VOUT_ HF

90 V

; 265 V

RMS

12 V

500 mA

±5%

50 mV

RMS

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

In order to minimize magnetic component size, the higher operating frequency device
(VIPer17) in the DIP7 package was selected. The average switching frequency (f

SW_avg

) is

115 kHz (typ.). The switching frequency is modulated by a triangular waveform at 250 Hz
between and where Δf
(frequency jittering) spreads the spectrum of the electromagnetic interference generated by

f

SWavg

-

fmΔ=

is 8 kHz (typ.). This frequency modulation

m

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.

Doc ID 14654 Rev 2 5/31

Board description AN2753

Figure 2. Schematic

1

2

J2

12V 500mA

CON2

R8

15k 1%

R9

3.9k 1%

C10

R6

L1 10uH

ZLG 47uF 25V

R13

1k

C9

1k

12

R10

C11

82k

33nF

3

VR1

TL431

2 1

43

OPTO1

PC817

81
7

DRAIN

VIPER17HN

VDD

BROWN OUT

5

U1

2

13

J3

JUMPER

F1

500mA F U SE

C7

SOURCE

FB

4 2

CONTROL

33nF

R12

10k

C6

3.3nF

CONT

3

R3

R5

47k

22k

2
1

J1 CON2

C4

C12

10nF

22uF 25V

7

4 691

ZL 470uF 25V

8

C8 Y1 1.8nF

TRANSFORMER

2

D4

STPS2H100

T1

5

D3

STTH1L06

D5

P6KE250

D1

BAT46

R1

10

C5

N.M

R14

D2

1N4148

C3

10uF 450V

4

T2

C2

2

1 3

10uF 450V

2

-+

3

BR1

1

R4

1600k

4

C1 X2

180k

R2

1600k

NTC1

10 Ohm NTC

12

t

6/31 Doc ID 14654 Rev 2

AN2753 Board description

Table 2. Bill of materials

Item Quantity Reference Part

11BR1 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

Doc ID 14654 Rev 2 7/31

Board description AN2753

1.1 Transformer

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

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.

Pins 1 & 2 shorted, pins 7 & 8 shorted

Fr=10 kHz, Ta = 20 °C

Figure 3. Bottom view Figure 4. Side view

Figure 5. Pins distances Figure 6. Electrical diagram

5

A

C

4

1

2

B

7

8

8/31 Doc ID 14654 Rev 2

AN2753 Testing the board

2 Testing the board

2.1 Typical 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 V
(500 mA). Figure 9 and Figure 10 show the same waveforms for the same load condition,
but the input voltages are the minimum (90 V

and 230 VAC when the load is the maximum

AC

) and the maximum (265 VAC).

AC

Figure 7. Drain current and voltage at full

load and nominal input voltages
(115 V

AC

)

Figure 9. Drain current and voltage at full

load and minimum input voltage
(90 V

AC

)

Figure 8. Drain current and voltage at full

load and nominal input voltages
(230 VAC)

Figure 10. Drain current and voltage at full

load and maximum input voltages
(265 VAC)

Doc ID 14654 Rev 2 9/31

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

OUT

1

-- -

2

2

L

I

fSWη⋅⋅ ⋅ ⋅=

PK

P

where L

is the transformer primary inductance, IPK is the drain peak current and η is the

P

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 I

is constant.

PK

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 V

IN_AC

, full load)

CH2: VFB 200 mV/Div (Light blue)
CH4: I

50 mA/Div (Green)

DRAIN

Time: 1 ms/Div

10/31 Doc ID 14654 Rev 2