U1

DPA426R

D2 SBG3045CT

D1 BAV19WS

C3

1 µF

100 V

D4

ES2D

VR1

SMCJ

100 A

2

9,10

6,7

NC

4

5

1

C5

220 nF

R2

68 Ω

1/4 W

C4

180 pF

200 V

C6

68 µF

10 V

C7 1 nF

1.5 kV

R14

10 Ω

U2

R15, R16

33 Ω

1/4 W

C9

2.2 nF

50 V

R3

8.8 kΩ

1%

R1

619 kΩ

1%

R4

1.0 Ω

L1

1 µH, 2.5 A

C23

4.7 µF

20 V

C1

1 µF

100 V

C2

1 µF

100 V

DL

SX

F

C

CONTROL

CONTROL

PI-3662-082603

DPA-Switch

T1

RTN

12 V, 5 A

U2

PC 357N1T

VR2

BTZ52C11

C10-C14

100 µF, 16 V

(OSCON)

C19

1 µF

16 V

C15-C18

47 µF, 16 V (CERAMIC)

R7

1 kΩ

C8

1 µF

16 V

R6

150 Ω

36-75 VDC

www.powerint.com

Design Idea DI-57

DPA-Switch

60 W DC-DC Converter

August 2003

DI-57

Application

Telecom

DPA426R

12 V

Power Output

60 W

Input Voltage

Output Voltage

Topology

Device

36-75 VDC

Flyback

Figure 1. DPA426R - 60 W, 12 V, 5 A DC-DC Converter.

®

™

Design Highlights

• Low cost 400 kHz flyback design

• Simple Zener referenced 12 V output

• Efficiency – 82% at 36 VDC and full load

• Low component count

• Accurate line OV and UV protection

• Thermal, short circuit and output overload protection

• No current sense components

Operation

DPA-Switch greatly simplifies the design compared to a discrete

implementation. Resistor R1 programs the under/over voltages

and linearly reduces the maximum duty cycle with input voltage

to prevent core saturation during load transients. Resistor R3

programs the DPA-Switch current limit at 85% of nominal to

minimize fault and overload power. Drain voltage clamping

is provided by diode D4 and Zener diode VR1 with optional

components C4 and R2 to provide high frequency snubbing.

The output is rectified by diode D2 with optional high

frequency damping from components C9, R15 and R16. The

output capacitors are alternated to share the ripple current

evenly between the Oscon capacitors (C10-14) and the

ceramic capacitors (C15-C18). A final decoupling ceramic

capacitor C19 is placed at the output pins of the power supply.

Output regulation is taken from the +12 V output. Zener

diode VR2 is DC-biased by resistor R7 with the opto-diode

of U2 providing feedback and resistor R6 programming the

gain. Optional capacitor C8 implements a soft-finish network

to slow the rise of the output voltage at start-up.