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Design Idea DI-56

DPA-Switch

19.2 W DC-DC Converter

September 2003

DI-56

Application

Telecom

DPA425R

±12 V

Power Output

19.2 W

Input Voltage

Output Voltage

Topology

Device

36-75 VDC

Flyback

Figure 1. DPA425R - 19.2 W,

±12 V, 0.8 A, DC-DC Converter.

®

™

Design Highlights

• Low cost 400 kHz flyback design

•

±12 V outputs at ±5% accuracy

• Highly efficient diode rectification design - 80% at 48 V

• 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 77% of nominal to

minimize fault and overload power. Drain voltage clamping

is provided by Zener diode VR1.

Output regulation is taken from the +12 V output. The -12 V

output is magnetically coupled. Shared regulation of +12 V

and -12 V may be used if better cross-regulation is required

between the two outputs. Optional resistor R7, diode D3 and

capacitor C16 implement a soft-finish network to slow the

rise of the output voltage at start-up, preventing overshoot.

The bias winding provides operating power to the

DPA-Switch. The regulation is fed back from the secondary

through the opto-transistor of U2. The DPA-Switch will go

into auto-restart in the event of optocoupler (U2) failure, or

output short circuit. The optional resistor R5 and Zener diode

VR2 provide a fail-safe output regulation path, limiting the

instantaneous output overvoltage in the event of U2 failure.

D

S

C

L

F

X

CONTROL

PI-3649-081103

R11

10.0 kΩ

1%

R9

220 Ω

R10

38 kΩ

1%

R14

10 Ω

R4

1.0 Ω

1%

R5

180 Ω

L2

300 nH

L3

300 nH

L1

1 µH

2.5 A

C4

4.7 µF

D1 BAV19W5

D3

BAVAW5

D20

MBR360

R3

10 kΩ

1%

R1

619 kΩ

1%

U1

DPA425R

R6

560 Ω

VR2

5.1 V

R7

10 kΩ

R12

5.1 Ω

1%

C14

1 µF

C6

68 µF

10 V

C5

220 nF

C16

10 µF

16 V

U3

LM41

AIM3

U2

C13

100 nF

C22

100 µF

16 V

C32

100 µF

16 V

C33

1 µF

C30

100 µF

16 V

C7

1 nF

1.5 kV

1

NC

8

7

6

5

2

3

4

D30

MBR360

C20

100 µF

16 V

C1- C2

1 µF

100 V

C3

1 µF

100 V

VR1

SMBJ

130

C21

100 µF

16 V

C31

100 µF

16 V

C23

1 µF

+V

IN

36-75 VDC

-V

IN

DPA-Switch

+12 V,

0.8 A

RTN

RTN

-12 V,

0.8 A