DI-31 View Datasheet(PDF) - Power Integrations, Inc
Part Name
Description
MFG CO.
'DI-31' PDF : 2 Pages View PDF
1
2
Design Idea DI-31
®
DPA-Switch™ 5 V, 70 W DC-DC
Converter with Synchronous Rectification
Application
Device
DC-DC Converter 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
simple self-driven synchronous rectification
Operation
The 70 W converter shown in Figure 1 benefits from many of
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
of additional components would increase the cost of this
converter significantly.
R1 programs the input UV/OV thresholds. The tight tolerance
of the UV/OV thresholds limits the range of gate drive voltages
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.
Capacitor C9, diodes D1-D2, and inductor L2 form a resonant
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
and overload conditions. Capacitor C12 and Resistor R7
damp secondary switching spikes and help to reset T1.
Key Design Points
• For nominal undervoltage set point V :
UV
R1 = (VUV - 2.35 V)/50 µA. VOV = (R1 x 135 µA) + 2.5 V.
• Locate C10, C11, and R3 close to the U1 CONTROL pin,
with ground connections returned to SOURCE pin.
+ VIN
36-75 VDC
L1
1 µH
2.5 A
C7 1 nF
1.5 kV
T1
1
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
C1, C2
1 µF
100 V
-VIN
D1
ESD1
6,7
R1
619 kΩ
2
D4
Q1-Q3 42CTQ30S
SI4842DY
C3, C4,
C5, C6
1 µF 100 V
(x4)
L2
220 µH
VR1
SMBJ
150
D2
ESD1
C9
150 pF
200 V
D
S
C12 2.2 nF, 50 V
3
R7
5
L5
1Ω
D3 2.2 mH
BAV19WS 40 mA
D5
BAV19WS
4
L DPA-Switch
CCOONNTTRROOLL
C
U1
DPA426R
XF
C10
220 nF
R2
6.8 kΩ
1%
C8
1 µF
25 V
R3
1.0 Ω
C11
68 µF
10 V
U2
PC357N1T
C23
10 µF
10 V
U2
R13
10 kΩ
D6
BAV19WS
R11
150 Ω
U3
LM431AIM3
R15
10.0 kΩ
1%
C22
100 nF
R10
5.1 Ω
R14
220 Ω
C21 1 µF
R16
10.0 kΩ
1%
5 V, 14 A
C20
1 µF
10 V
RTN
Figure 1. DPA426 70 W, 5 V, 14 A DC-DC Converter.
PI-3375-121602
DI-31
www.powerint.com
December 2002
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