DER-19

TOP245P Multiple Output Set Top Box

March 30, 2004

Page 12 of 25

Power Integrations, Inc.

Tel: +1 408 414 9200 Fax: +1 408 414 9201

www.powerint.com

8

Transformer Spreadsheets

This design was produced using PIExpert assuming a TOP245P device with a current

limit capability of 1.1A and an Rdson of 4

Ω. The data below reflects the full continuous

load, which gives approximately 0.7A peak primary current. The transformer has been

designed to operate with safe flux levels with primary currents of up to 1.2A allowing for

the peak power capability.

Power Supply Input

VACMIN

Volts

195

Min Input AC Voltage

VACMAX

Volts

265

Max Input AC Voltage

FL

Hertz

50

AC Main Frequency

TC

mSeconds

1.81

Bridge Rectifier

Conduction Time

Estimate

Z

0.68

Loss Allocation Factor

N

%

74.0

Efficiency Estimate

Power Supply

Outputs

VOx

Volts

3.30

5.00

12.00

20.00 Output Voltage

IOx

Amps

3.000

2.000

0.500

0.300 Output Current

VB

Volts

15.00

Bias Voltage

IB

Amps

0.006

Bias Current

Device Variables

Device

TOP245P

Device Name

PO

Watts

31.99

Total Output Power

VDRAIN

Volts

678

Maximum Drain Voltage

Estimate (Includes

Effect of Leakage

Inductance)

FS

Hertz

132000

Device Switching

Frequency

KRPKDP

0.70

Ripple to Peak Current

Ratio

KI

1.00

External Current Limit

Ratio

IP

Amps

0.75

Peak Primary Current

IRMS

Amps

0.31

Primary RMS Current

DMAX

0.36

Maximum Duty Cycle

Power Supply Components

Selection

CIN

uFarads

47.0

Input Filter Capacitor