Design Idea DI-57
™
DPA-Switch
60 W DC-DC Converter
Application
Telecom
Device
DPA426R
Power Output
60 W
Input Voltage
36-75 VDC
Output Voltage
12 V
Topology
Flyback
®
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
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.
R15, R16
33
Ω
1/4 W
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
C7 1 nF
1.5 kV
+
VIN
L1
36-75 VDC
1
µH,
2.5 A
2
R14
10
Ω
T1
9,10
C9
2.2 nF
50 V
C10-C14
100
µF,
16 V
(OSCON)
C19
1
µF
16 V
12 V, 5 A
VR1
SMCJ
100 A
NC
6,7
D2 SBG3045CT
D1 BAV19WS
C15-C18
47
µF,
16 V (CERAMIC)
RTN
D4
ES2D
4
1
5
C23
4.7
µF
20 V
U2
R7 U2
1 kΩ
R1
619 kΩ
1%
C1
1
µF
100 V
C2
1
µF
100 V
C3
1
µF
100 V
C4
180 pF
200 V
PC 357N1T
DPA-Switch
U1
DPA426R
D
L
CONTROL
R6
150
Ω
C
S
X
F
R2
68
Ω
1/4 W
-VIN
R3
8.8 kΩ C5
1% 220 nF
R4
1.0
Ω
C6
68
µF
10 V
C8
1
µF
16 V
VR2
BTZ52C11
Figure 1. DPA426R - 60 W, 12 V, 5 A DC-DC Converter.
DI-57
PI-3662-082603
www.powerint.com
August 2003
POWERINT [ POWER INTEGRATIONS, INC. ]
