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A

9/02

DI-24

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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.

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

Core

Bobbin

Winding Details

Winding Order

(pin numbers)

Inductance

Primary Resonant

Frequency

TRANSFORMER PARAMETERS

Table 1. Transformer Construction Information.

PR1408

Siemens N87 material, ungapped

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

Primary: 7T + 8T, 27 AWG

Secondary: 4T x 27 AWG

Primary (4-3), tape, Secondary

(5,6-7,8), Tape, Primary (3-1),tape

Primary: 450 µH ± 25%, Leakage 1 µH (max)

3.8 MHz (minimum)

Table 2. Output Inductor Construction Information.

Core

Bobbin

Winding Details

Winding Order

(pin numbers)

Inductance

Pins 5,6-7,8

OUTPUT INDUCTOR PARAMETERS

PR1408 Siemens N87 material

Gap for A

2

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

Bias: 18T, 32 AWG, Main: 7T, 2x24 AWG

Bias (1-2), tape, Main winding (7,8-5,6), tape

8 µH ± 10%

90

80

75

85

0

10

20

30

40

Output Power (W)

60

65

70

Figure 2. Efficiency vs. Output Power.

Key Design Points

• For nominal under-voltage set point V

R1 = (V

• Select C9 such that the core resets at V

voltage

≤170 V at V

be added, adjusting C9 accordingly.

• Zener VR1 safely limits the DRAIN voltage below BV

DSS

and guarantees transformer reset.

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

for optimum loop stability.

• At zero load, maximum input voltage, the bias voltage

across C4 should be

≥8 V (12 V to 15 V under nominal

conditions).

• 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.

• Consult AN-31 and EPR-21 for additional design tips and

information.