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Design Idea DI-30
TOPSwitch-GX

180 W PC Main SFX Supply

December 2002

DI-30

®

Application

PC Main

TOP249Y

3.3 V / 5 V / 12 V / -12 V

Power Output

180 W

Input Voltage

Output Voltage

Topology

Device

90-130 VAC / 180-265 VAC

Forward

Design Highlights

• 180 W cont. (200 W peak) in PC SFX form factor
• Includes passive power factor correction (PFC)
• TOPSwitch-GX integrated features enable extremely low

component count

• Meets 1 W standby spec (0.91 W input, 0.5 W output)
• High efficiency (71% minimum)
• Integrated line undervoltage and overvoltage detection
• Low EMI due to frequency jitter
• SOURCE referenced TO-220 tab lowers conducted EMI
• Maximum duty cycle reduction (DC

MAX

) prevents transformer

saturation for fault and transient loads

• Uses conventional magamp for 3.3 V output
• Meets CISPR22B/EN55022B conducted EMI

Operation

TOPSwitch-GX integrates many features designed for use with
forward converters. Passive power factor correction (PFC) is
implemented using inductors LPFC1 and LPFC2. Transistors
Q4, Q6, R1, R2, R3, R5, and R6 form an active capacitor (C2,

Figure 1.

180 W (200 W pk.) PC Main Power Supply Schematic (Note: Schematic does not include transformer Y-capacitor)

.

C3) balancing circuit, operating only as needed to minimize
zero-load power consumption.

Resistors R3, R5 and R6 implement start-up undervoltage
lockout, which prevents the supply from starting below
180 VDC. Components R4, R14, Q1 and R30 implement an
independent undervoltage using the X pin, which allows the
supply to continue delivering power all the way down to
140 VDC (increasing holdup time). Resistor R7 provides
additional hysteresis.

The primary side components D1, VR3-5 and C4, along with
secondary side C9 and R30, implement the Zener/capacitor
reset/clamp circuit. This circuit provides reset voltage for the
transformer and clamps the DRAIN pin voltage to a safe level
(<~600 V) under all conditions.

The reset circuit works in conjunction with the DC

MAX

reduction circuit (R8, R36, C22, VR19 and D18) to limit the
maximum duty cycle and prevent transformer saturation
under fault and transient conditions.

®

C13

220 µF

63 V

C3

470 µF

200 V

C2

470 µF

200 V

L

G

N

RTN

+5 V

+12 V

R20

270 kΩ

R16

1 kΩ

U5

TL431

D

S

C

L

F

X

CONTROL

R19

4.12 kΩ

1%

F1

4 A

RV1

275 V, 14 mm

R10

560 K
1/2 W

CX2

0.33 µF

250V

CY4

2.2 nF

(Safety)

RT1

10 Ω

CY3

2.2 nF

(Safety)

JP9

CX1

0.047 µF

250 VAC

L7

8.2 mH

BR1

KBL06

To AC Selector

Switch

R1

330 kΩ

R2

330 kΩ

D1

1N5407

R3

2.2 MΩ

R5

180 kΩ

R6

2.2 MΩ

R8

130 kΩ

1%

R14

75 kΩ

R12

12 kΩ

R30

3.3 kΩ

Q1

2N3908

C22

100 pF

50 V

C10

1 nF
50 V

C20

330 pF

50 V

D7

MBR3045

R36

43.2 kΩ

1%

R13

10 Ω

D18

BAV20

VR19

1N5229

R4

2.2 MΩ

R7

560 kΩ

R11

300 Ω

Coupled

choke

L1

13 µH

R30

1 Ω

1 W

D8

MBR6045

C9

47 nF

50 V

C12

2200 µF

6.3 V

C11

1000 µF

16 V

L2

0.5 µH

U2

SFH615A-2

R17

15 kΩ

C16

100 nF

50 V

D6

BAV20

C8

0.033

µ

F

50 V

R9

47 Ω

C6

47

µ

F

16 V

C7

100 nF

50 V

D105

1N4148

Remote
ON/OFF

R38

5.1 kΩ

U3

LTV817

R37

10 kΩ

R106

27 kΩ

+12 V STBY

C23

33 nF

50 V

VR3

BZY97C-

200

C4

2.2 nF

1 kV

VR4

BZY97C-

180

VR5

BZY97C-

180

D20

UF4002

C5

1

µ

F

100 V

C27

330 pF

50 V

R11

330 Ω

LM

320

C25

1 µF

50 V

TO
MAGAMP OUT
(3.3 V)

- 12 V

R18

4.74 kΩ

1%

R15

1.8 kΩ

C17

100 nF

50 V

C24

330 µF

25 V

Q7

2N3904

PI-3384-120902

TOPSwitch-GX

U1

TOP249

2

1

13

14

11,12

8, 9, 10

4

3

4

5

1, 2

7, 8

3

6

Q6

MPSA92

Q4

MPSA42

R21

270 Ω

LPFC1

LPFC2

www.powerint.com

B
12/02

DI-30

WORLD HEADQUARTERS
AMERICAS
Power Integrations, Inc.
San Jose, CA 95138 USA
Customer Service:
Phone:

[phone]

Fax:

[phone]

e-mail: [e-mail]

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Power Integrations International
Holdings, Inc.
China
Phone:

[phone]

Fax:

[phone]

e-mail: [e-mail]

SINGAPORE
Power Integrations, Singapore
Republic of Singapore 308900
Phone:

[phone]

Fax:

[phone]

e-mail: [e-mail]

JAPAN
Power Integrations, K.K.
Keihin-Tatemono 1st Bldg.
Japan
Phone:

[phone]

Fax:

[phone]

e-mail: [e-mail]

EUROPE & AFRICA
Power Integrations (Europe) Ltd.
United Kingdom
Phone:

[phone]

Fax:

[phone]

e-mail: [e-mail]

KOREA
Power Integrations
International Holdings, Inc.
Seoul, Korea
Phone:

[phone]

Fax:

[phone]

e-mail: [e-mail]

TAIWAN
Power Integrations
International Holdings, Inc.
Taipei, Taiwan
Phone:

[phone]

Fax:

[phone]

e-mail: [e-mail]

INDIA (Technical Support)
Innovatech
Bangalore, India
Phone:

[phone]

Fax:

[phone]

e-mail: [e-mail]

APPLICATIONS HOTLINE APPLICATIONS FAX
World Wide [phone] World Wide [phone]

Figure 2. Magamp for Independent 3.3 V Secondary Regulation.

The components R12, C7, R38, Q7, C23, R37, U3, R106 and
D105 implement the remote ON/OFF drive circuit. During
the ON state, U3 and hence Q7 conduct, pulling the X pin to
SOURCE via resistor R12 (which sets the current limit).

During the OFF state, U3 and Q7 are off, allowing the X pin
to be pulled high by the +15 V standby supply via R38 and R12
and putting the TOPSwitch-GX into the OFF state. Components
R38 and D105 reduce device consumption to around 2mW by
supplying external current to the CONTROL pin from the
+15 V standby supply. Resistor R11 is required to allow
external bias feed.

Key Design Points

• The passive PFC inductors (LPFC1 and LPFC2) are

constrained by both thermal and efficiency requirements.
Design of these inductors is not covered in this Design Idea.

• Transformer reset: Use recommended Zener/capacitor

clamp/reset circuit to maintain drain voltage < 600 V and
DC

MAX

reduction to prevent transformer saturation.

• Maintain maximum flux density on transformer (T1)

< 2500 gauss.

• Check for balanced currents on coupled inductor (L1) for

all load combinations.

• Use PI Expert (PIXls) Design Spreadsheet and refer to

Application Note AN-30 for details on designing forward
converters with TOPSwitch-GX.

This particular PC SFX 12 specification delivers a larger
proportion of power on the 12 V winding; efficiency would be
lower if that power were drawn from the 3.3 V output.

Due to the complexity of this design it is not possible to include
all details in this Design Idea. An Engineering Prototype Report
(EPR) will be available for this design Dec. 2000. For updates
and all other information please refer to Power Integrations'
Web site.

For the latest updates, visit our Web site: www.powerint.com
Power Integrations reserves the right to make changes to its products at any time to improve reliability or manufacturability.
Power Integrations does not assume any liability arising from the use of any device or circuit described herein, nor does it convey any
license under its patent rights or the rights of others. The products and applications illustrated herein (including circuits external to the
products and transformer construction) may be covered by one or more U.S. and foreign patents or potentially by pending U.S. and foreign
patent applications assigned to Power Integrations. A complete list of Power Integrations’ patents may be found at www.powerint.com.

The PI Logo, TOPSwitch, TinySwitch, LinkSwitch and EcoSmart are registered trademarks of Power Integrations, Inc.
PI Expert is a trademark of Power Integrations, Inc. ©Copyright 2002, Power Integrations, Inc.

3.3 V

RTN

RTN

PI-3385-093002

D11

UF4002

D10

UF4002

R22

3 Ω

Q2

TIP32

D9

MBR2045

L4

20 µH

L5

0.5 µH

R34

33 Ω

R27

390 Ω

R23

1 kΩ

R25

2.7 kΩ

C18

0.1 µF

50 V

R24

3.84 kΩ

1%

R26

10 kΩ

1%

U8

TL431

C21

1 µF

50 V

L3

Mag Amp

6 Turns

C14

1200 µF

10 V

C15

1200 µF

10 V

FROM MAIN

CONVERTER
5 V WINDING