®
Design Idea DI-51
DPA-Switch™
5 W Flyback DC-DC Converter
Topology
Flyback
Device
Power Output
Input Voltage
Output Voltage
Application
DC-DC Converter
5 W
36-75 VDC
DPA423R
5 V
Design Highlights
Resistor R3 programs the internal current limit of the
DPA423Rto53%ofnominal.Thislimitstheoverloadpower
that can be delivered in a fault condition.
• Small footprint: 35 mm x 20 mm (1.4 in. x 0.8 in.)
• High efficiency flyback (>80% min.)
• 8.8 W per cu. in.
Zener VR1 clamps the leakage inductance spikes to keep the
DRAIN voltage at a safe level. The bias supply for U1 is
provided from the auxiliary flyback transformer winding
(pins 2 and 4), rectified and filtered by diode D1 and
capacitor C23.
• Low component count
• Accurate line OV and UV protection
• Thermal, short circuit and output overload protection
• No current sense components
A snubber for diode D2 (capacitor and resistor) can be used,
but was not needed in this application. Inductor L2 and
capacitor C12 form a post filter to reduce high frequency
output switching ripple. A soft-finish network, C18, D3 and
R7, eliminates output turn-on overshoot. The remaining
components provide output voltage regulation and loop
compensation.
Operation
DPA-Switchgreatlysimplifiesthedesigncomparedtoadiscrete
implementation. Resistor R1 sets the input under/over voltages
to 33 V and 86 V, respectively. Including tolerances, these
thresholds guarantee the converter is operational between 36 V
and 75 V without the cost of additional line sense components.
C7 1 nF
R14
1.5 kV
10 Ω
L2
300 nH
6 A
L1
C12
100 µF
10 V
C10
C11
+ V
36-75 VDC
D2 SL23
1A/30 V
10 µH
IN
100 µF 100 µF
0.85 A
5 V, 1 A
RTN
10 V 10 V
T1
7,8
1
5,6
FL
D1 BAV19WS
2
3
C23
4.7 µF
20 V
4
R1
619 kΩ
1%
R10
18 kΩ
1%
U2
R7
10 kΩ
U2
C1
0.22 µF
100 V
C2
1 µF
100 V
DPA-Switch
C16
220 nF
U1
D3
BAV19WS
DPA423R
R6
R12
D
S
L
150 Ω
5.1 Ω
CONTROL
C
C17
1 µF
R9
220 Ω
C18
10 µF
10 V
R4
X
F
R3
1.0 Ω
VR1
14.4 kΩ
C5
47 nF
SMBJ
150 A
1%
U3
LM431AIM3
C6
68 µF
10 V
R11
18 kΩ
1%
-V
IN
PI-3547-062403
Figure 1. DPA-Switch Flyback DC-DC Converter.
.
July 2003
DI-51
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