Design Idea DI-56
™
DPA-Switch
19.2 W DC-DC Converter
Application
Telecom
Device
DPA425R
Power Output
19.2 W
Input Voltage
36-75 VDC
Output Voltage
±12
V
Topology
Flyback
®
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
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.
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
C7
R14
1 nF
1.5 kV 10
Ω
+V
IN
36-75 VDC
L1
1
µH
2.5 A
1
8
7
NC
6
4
R1
619 kΩ
1%
DPA-Switch
U1
DPA425R
C
D30
MBR360
C30
C31
100
µF
100
µF
16 V
16 V
C32
L3
100
µF
300 nH
16 V
C33
1
µF
+12 V,
0.8 A
RTN
RTN
C20
D20 100
µF
MBR360 16 V
D1 BAV19W5
C21
100
µF
16 V
L2
300 nH
C22
100
µF
16 V
C23
1
µF
R10
38 kΩ
1%
C13
100 nF
R12
5.1
Ω
1%
C14
1
µF
C16
10
µF
16 V
U3
LM41
AIM3
R9
220
Ω
R11
10.0 kΩ
1%
PI-3649-081103
5
2
-12 V,
0.8 A
C1- C2
1
µF
100 V
C3
1
µF
100 V
C4
3 4.7
µF
R5
180
Ω
D3
BAVAW5
U2
R7
10 kΩ
R6
560
Ω
VR2
5.1 V
D
L
CONTROL
S
X
F
VR1
SMBJ
130
-V
IN
C5
220 nF
R3
10 kΩ
1%
R4
1.0
Ω
1%
C6
68
µF
10 V
Figure 1. DPA425R - 19.2 W,
±
12 V, 0.8 A, DC-DC Converter.
DI-56
www.powerint.com
September 2003
POWERINT [ POWER INTEGRATIONS, INC. ]
