Design Idea DI-31
™
DPA-Switch
5 V, 70 W DC-DC
Converter with Synchronous Rectification
Application
DC-DC Converter
Device
DPA426R
Power Output
70 W
Input Voltage
36-75 VDC
Output Voltage
5V
®
Topology
Forward
Design Highlights
•
•
•
•
•
•
Extremely low component count
High efficiency, 90% using synchronous rectification
No current sense resistor or current transformer required
Output overload, open loop and thermal protection
Accurate input under/overvoltage meets ETSI standards
300 kHz switching frequency – optimizes efficiency using Capacitor C9, diodes D1-D2, and inductor L2 form a resonant
simple self-driven synchronous rectification
snubber that recycles leakage and magnetizing energy stored
in T1, and also helps to reset T1. Zener diode VR1 provides
a hard voltage limit and only conducts during output transient
Operation
and overload conditions. Capacitor C12 and Resistor R7
The 70 W converter shown in Figure 1 benefits from many of damp secondary switching spikes and help to reset T1.
the
DPA-Switch
integrated features. In particular, no external
current sense components are required. In a discrete
implementation, an expensive current transformer and a number
Key Design Points
of additional components would increase the cost of this • For nominal undervoltage set point V :
UV
converter significantly.
R1 = (V
UV
- 2.35 V)/50
µA.
V
OV
= (R1
x
135
µA)
+ 2.5 V.
• Locate C10, C11, and R3 close to the U1 CONTROL pin,
R1 programs the input UV/OV thresholds. The tight tolerance
with ground connections returned to SOURCE pin.
of the UV/OV thresholds limits the range of gate drive voltages
C7 1 nF
1.5 kV
+
VIN
36-75 VDC
L1
1
µH
2.5 A
1
applied to MOSFETs Q1 to Q6, eliminating the need for gate
voltage clamp circuitry. The self-driven synchronous
rectification configuration is therefore very simple, with R4
to R6 filtering voltage spikes at the gates of Q1, Q2 and Q3
and D4 preventing the body diodes of Q4, Q5 and Q6 from
conducting.
T1
9,10
R4-R6
10
Ω
Q4-Q6
SI4842DY
L3
3.8
µH
20 A
C13, C14,
C15, C16, C17
100
µF
10 V
(x5)
L4
100 nH
20 A
C18, C19
100
µF
10 V
5 V, 14 A
C20
1
µF
10 V
RTN
D1
ESD1
R1
619 kΩ
6,7
2
D4
Q1-Q3
42CTQ30S
SI4842DY
C12 2.2 nF, 50 V
R7
1
Ω
U2
3
C1, C2
1
µF
100 V
C3, C4,
C5, C6
1
µF
100 V
(x4)
C9
150 pF
200 V
5
4
D
L
CONTROL
CONTROL
L5
D3
2.2 mH
BAV19WS 40 mA
D5
BAV19WS
C8
1
µF
25 V
R13
10 kΩ
D6
BAV19WS
R15
10.0 kΩ
1%
C22
100 nF
R10
5.1
Ω
R14
220
Ω
C21 1
µF
DPA-Switch
C
L2
220
µH
S
U1
DPA426R
R11
150
Ω
U2
PC357N1T
C23
10
µF
10 V
U3
LM431AIM3
X
F
-VIN
VR1
SMBJ
150
D2
ESD1
R3
1.0
Ω
C10
220 nF
R2
6.8 kΩ
1%
C11
68
µF
10 V
R16
10.0 kΩ
1%
PI-3375-121602
Figure 1. DPA426 70 W, 5 V, 14 A DC-DC Converter.
DI-31
www.powerint.com
December 2002
POWERINT [ POWER INTEGRATIONS, INC. ]
