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. POWER INTEGRATIONS MAKES NO WARRANTY HEREIN AND SPECIFICALLY DISCLAIMS ALL

WARRANTIES INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS

FOR A PARTICULAR PURPOSE, AND NON-INFRINGEMENT OF THIRD PARTY RIGHTS. The products and applications

illustrated herein (transformer construction and circuits external to the products) 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. Power Integrations grants its

customers a license under certain patent rights as set forth at http://www.powerint.com/ip.htm.

The PI logo,

TOPSwitch, TinySwitch,LinkSwitch, DPA-Switch,PeakSwitch,EcoSmart,

Clampless,

E-Shield,Filterfuse,StackFET, PI ExpertandPI FACTS are trademarks of Power

Integrations, Inc. Other trademarks are property of their respective companies. ©Copyright 2007, Power Integrations,

For the latest updates, visit

www.powerint.com

Rev. A 1/07

Power Integrations

5245 Hellyer Avenue

San Jose, CA 95138

Phone: 1-408-414-9200

Apps: 1-408-414-9660

Apps Fax: 1-408-414-9760

For a complete listing of worldwide

sales offices, please visit

www.powerint.com

Table 2. Transformer Construction Information.

Key Design Points

• The secondary side bias current, set by R7, should be kept

lowtominimizelightloadandno-loadpowerconsumption.

• The output voltage that is reflected across the transformer

(V

primary side RCD clamp.

•Optimizetheturnsratioofthetwooutputsforvoltage

centering.

• For good output cross regulation, design for continuous

conductionmode(minimizethevalueofK

PI Xls

spreadsheet).

• Use a Schottky diode for D3 to limit EN/UV pin >-0.3V.

• AstheforwarddropofD3isafunctionoftemperature,diode

type and current, use a schottky diode. Do not reduce the

value of R3, and verify EN/UV pin absolute maximum

ratingsareobservedatlowtemperatures(~<-10°C).

TRANSFORMER PARAMETERS

Core Material

EF20 TDK PC40, or equivalent

A

2

Bobbin

EF20, 10 pin (5 + 5)

Winding Details

Shield: 23T, Primary: 95T

Shield: 9T (trifilar), –5 V: 5T,

–12 V: 7T

Primary

Inductance

1.28 mH

±10%

Figure 3. Conducted EMI at 230 VAC, Full Load.

Figure 2. Full Load Efficiency vs. Input Voltage.

-5 V

-12 V

20% on -5 V,

100% on -12 V

-5.05 V

-11.49 V

100% on -5 V,

20% on -12 V

-5.03 V

-12.95 V

100% on -5 V,

5% on -12 V

-5.02 V

-13.90 V

Table 1. Worst Case Cross Regulation at 85 VAC.

85

115

175

145

235

205

265

AC Input Voltage (V)

82

80

78

76

74

72

70

Nominal Load

1.0

EN55022B Limits

0.15

10.0

70.0

-20

-10

0

10

20

30

40

50

60

80

70

MHz

QP

AV

QP

AV

• ThevalueofR4canbeusedtomakesmalloutput

voltageadjustments.

• Theregulationpointisthesumofthevoltageratingof

VR1,V

• BiasingtheZenerbelowitstestcurrentlowersits

voltagedrop,inthiscaseto~4.3V.

•Selecttransformerwiregaugesizessothateachwinding

layer occupies the entire bobbin width (lowers leakage

inductanceandimprovesoutputcrossregulation).

• Use option to add E-ShieldwindingsinPI Transformer

Designer

softwaretoreduceconductedEMInoise

generation.

• No-load power consumption can be lowered by adding a

biaswindingtofeedthesupplycurrentofU1intotheBPpin.