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12/02

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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.

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

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Power Integrations, K.K.

Keihin-Tatemono 1st Bldg.

Japan

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+81-45-471-1021

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+81-45-471-3717

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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

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TAIWAN

Power Integrations

International Holdings, Inc.

Taipei, Taiwan

Phone:

+886-2-2727-1221

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+886-2-2727-1223

e-mail: taiwansales@powerint.com

INDIA (Technical Support)

Innovatech

Bangalore, India

Phone:

+91-80-226-6023

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APPLICATIONS HOTLINE

APPLICATIONS FAX

World Wide +1-408-414-9660

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Figure 2. Efficiency vs. Output Power.

Key Design Points

• For nominal under-voltage set point V

R1 = (V

• Zener VR1 voltage is 130 V to safely limit the DRAIN

voltage below V

• Opto U2 should have a CTR of between 100% and 200%

for optimum loop stability.

• Set resonance of L2 and C13 + C14 to beyond loop

crossover frequency (typically 5% to 10% of switching

frequency).

• Good layout practices should be followed:

- Locate C5, C6 and R4 close to U1, with grounds

returned to the SOURCE pin.

- Primary return should be connected to the DPA-Switch

tab, not the SOURCE pin.

-Minimize the primary and secondary loop areas to

reduce parasitic leakage inductance.

Table 1. Transformer Construction Information.

Core Material

Bobbin

Winding Order

(pin numbers)

Inductance

Primary Resonant

Frequency

PR1408

Siemens N87

Gap for 340 nH/T

2

P1408 8 pin (B&B B-096 or equivalent)

Primary (4-FL), tape, Bias (2-3), tape,

Secondary (5,6-7,8), tape,

Primary (FL-1), tape

Primary: 6T + 6T, 2 x 27 AWG

Secondary: 3T, 4 x 25 AWG

Bias: 6T, 32 AWG

3.8 MHz (minimum)

Primary: 49 µH ±10%, Leakage: 1 µH (max)

Transformer Parameters

Winding Details

20

0

510

15

20

25

Output Current (W)

0

40

80

100

60

36 VDC

48 VDC

60 VDC

72 VDC