www.powerint.com

A

9/02

DI-22

Table 1. Transformer Construction Information.

To reduce winding and diode dissipation the secondary is split

into two windings and diode OR’ed into the output capacitors

(C2, 3). Regulation is provided by a secondary side reference

(U3), the output voltage sensed by R4, R13 and R6.

Key Design Points

• D1 and VR1 clamp leakage inductance spikes. A Zener

clamp provides lower zero load consumption than an RCD

clamp and higher efficiency below full load.

• C11 reduces VR1 dissipation, raising efficiency.

• Additional differential filtering is provided by C13 and L3.

• C12 provides high frequency bypass, reducing high

frequency EMI.

• Use foil windings to reduce dissipation and reduce leakage

inductance.

• Sandwich secondary winding between two halves of

primary to reduce leakage inductance.

• High core temperature reduces saturation flux density.

Keep flux density below 3000 gauss (0.3 T) to prevent

saturation.

• Use 100 V Schottky diodes for highest efficiency.

• Good layout practices should be followed:

- Locate C8, R3, C5, R9, R10 and R11 close to U1.

- Power and signal source currents should be separated,

joined using a Kelvin connection at the SOURCE pin.

-Minimize the primary and secondary loop areas to reduce

parasitic leakage and EMI.

• Consult DAK-11 and EPR-11 for more information.

WORLD HEADQUARTERS

AMERICAS

Power Integrations, Inc.

San Jose, CA 95138 USA

Customer Service:

Phone:

+1 408-414-9665

Fax:

+1 408-414-9765

e-mail: usasales@powerint.com

CHINA

Power Integrations International

Holdings, Inc.

China

Phone:

+86-755-8367-5143

Fax:

+86-755-8377-9610

e-mail: chinasales@powerint.com

SINGAPORE

Power Integrations, Singapore

Republic of Singapore 308900

Phone:

+65-6358-2160

Fax:

+65-6358-2015

e-mail: singaporesales@powerint.com

JAPAN

Power Integrations, K.K.

Keihin-Tatemono 1st Bldg.

Japan

Phone:

+81-45-471-1021

Fax:

+81-45-471-3717

e-mail: japansales@powerint.com

EUROPE & AFRICA

Power Integrations (Europe) Ltd.

United Kingdom

Phone:

+44-1344-462-300

Fax:

+44-1344-311-732

e-mail: eurosales@powerint.com

KOREA

Power Integrations

International Holdings, Inc.

Seoul, Korea

Phone:

+82-2-782-2840

Fax:

+82-2-782-4427

e-mail: koreasales@powerint.com

TAIWAN

Power Integrations

International Holdings, Inc.

Taipei, Taiwan

Phone:

+886-2-2727-1221

Fax:

+886-2-2727-1223

e-mail: taiwansales@powerint.com

INDIA (Technical Support)

Innovatech

Bangalore, India

Phone:

+91-80-226-6023

Fax:

+91-80-228-9727

e-mail: indiasales@powerint.com

APPLICATIONS HOTLINE

APPLICATIONS FAX

World Wide +1-408-414-9660

World Wide +1-408-414-9760

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 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 and EcoSmart are registered trademarks of Power Integrations, Inc.

PI Expert is a trademark of Power Integrations, Inc. ©Copyright 2002, Power Integrations, Inc.

TRANSFORMER PARAMETERS

Core Material

FPQ26/20-A

TDK PC40 gappped for A

2

Bobbin

TDK BPQ26/20-1112CP

Winding Details

Primary: 9T + 9T, 2 x 26 AWG

Shield: 1T, 8 mm x 0.015 mm Cu foil

Secondary 1: 3T, 3 x 26 AWG T.I.W.

Secondary 2: 3T, 3 x 26 AWG T.I.W.

Bias: 2T, 8 mm x 0.015 mm Cu foil

(T.I.W. = Triple Insulated Wire)

Inductance

Primary: 273 µH ± 10%,

Leakge: 3 µH (maximum)

Primary Resonant

Frequency

1.5 MHz (minimum)

Winding Order

(Pin Numbers)

Primary (2-1), Shield (1-NC),

tape, Secondary 1 (12-9),

Secondary 2 (11-8),

Bias (6-5), tape, Primary (3-2), tape