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A

11/02

DI-43

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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 (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.

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

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Phone:

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APPLICATIONS HOTLINE

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Figure 2. P

Table 1. Transformer Construction Information.

Optional components D4, C11, and R7 implement soft finish

to limit startup overshoot. Resistor R7 discharges this soft-

finish capacitor at power down.

Key Design Points

• Use reflected voltage from 90 V to 120 V

• Compact layout for components D3, C6 and C7 will

improve efficiency. Make sure the both capacitors C6 and

C7 have equal secondary loop areas to balance the ripple

currents in each.

• Clamp: for lowest cost use an RCD clamp replacing Zener

VR1 with a power resistor. For best no-load performance,

use the Zener clamp as shown.

•Reference voltage: Use low current Zener secondary

reference with 5 mA bias current for lowest cost. Use

TL431 as shown for both better regulation accuracy and

no-load consumption (due to lower bias current 1 mA).

80

120

AC Input Voltage

.20

.15

.10

.05

0

.25

.30

.35

160

200

240

280

TRANSFORMER PARAMETERS

Core Material

EF25 Nippon Ceramic NC-2H

A

2

Bobbin

EF25 10 pin

(Miles Platts FE0100 with TBS-601)

Winding Details

1/2 Primary, tape, 1/2 primary (1-3),

tape, Bias (5-4), tape,

12 V (9-10, 6-7), tape

Inductance

Primary: 876

µH ± 10% at 132 kHz,

Leakage: 28

µH (maximum)

Primary Resonant Frequency

570 kHz (minimum)

Winding Order

(Pin Numbers)

Primary: 58T x 26 AWG

Bias: 2T x 26 AWG

12 V: 6T 4 x 25 AWG T.I.W.

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