www.powerint.com

A

9/02

DI-13

Key Design Points

• Design transformer for low leakage inductance.

• Varnish transformer to practically eliminate acoustic

noise - gluing not required.

• Maximum flux density of main transformer should be no

more than 3000 gauss.

• Use primary RCD clamp that allows no more than

600 V across the TinySwitch-II DRAIN and SOURCE

pins.

• Provide adequate copper area on PCB at the connection

to the TinySwitch-II SOURCE pin, for heatsinking.

Core: EF 12.6, gapped for A

L

Bobbin: Hical EF 12.6, 8 pin

Primary (3-1)

Shield winding (1-2)

Secondary (8-5)

1.25 mH

700 kHz (min)

50 µH

Core Material

Bobbin

Winding Order

Primary Inductance

Primary Resonant

Leakage Inductance (all

secondary windings shorted)

Transformer Parameters

Figure 2. Efficiency vs. Input Voltage.

Table 1. Transformer Construction Information.

For the latest updates, visit our Web site: www.powerint.com

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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.

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85

185

235

135

285

Input Voltage (VAC)

74%

72%

70%

68%

76%

78%

75

115 135

95

155

Input Voltage (VAC)

150

100

50

0

200

250

175 195 215 235 255 275

Figure 3. Efficiency vs. Input Voltage.