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Description of the Digital Phase-Shifted Full-Bridge Converter
12.3.3
Sensing Input Voltage on Secondary-Side
In
Figure 25
there is sample-and-hold circuit on the secondary side of the PWR050, which senses the
primary-side voltage. When the Q2 switch turns on, D5 turns on. The voltage on the winding (6, 7) of the
bias transformer T1 charges capacitor C9 to a voltage equal to VIN / N after the divider of R16 and R14,
where N is the turns ratio of T1. When Q2 turns off, D5 turns off, and the voltage on C9 is held until the
next switching period. The voltage on C9 is proportional to the input voltage. U4 is used to scale the
sampled voltage to the application.
PIN3
+
R13
C2
C7
3.01k
PIN4
330 µF
10µF
-VIN/VAUX RETURN
PIN1
PWRGND
+VIN
R48
R5
R6
150k
150k
150k
R7
150k
C3
+
10uF
PWRGND
+
C6
47 uF
C21
100nF
100nF
PIN2
-VIN
PWRGND
28
Using the UCD3138PSFBEVM-027
R3
C1
100
100pF
D3
C8
R10
150pF
4.99
R45
R4
165k
499
MMBD1204
D1
MUR1100ERLG
R2
U1
10
UCC28600D
6 VDD
7
OVP
8 STATUS
5
OUT
1 SS
3
CS
2 FB
4
GND
C5
R1
UCC28600D
C15
47.5k
220pF
PWRGND
Figure 25. PWR050 Bias Board Schematics
Copyright © 2013, Texas Instruments Incorporated
R12
D5
4.99
T1
3
7
4
6
D2
1
8
VAUXSEC
GND
2
5
R47
100
R11
100k
GND
C20
100pF
D4
GND
Q2
FQD3N60
R56
1.5k
C12
R46
220pF
2.4
R52
R43
12.1k
4.99k
C13
220pF
U2
4
1
R41
33.2k
3
2
C18
1
100nF
U3
TL431AQDBZ
2
3
R9
GND
4.42k
GND
C11
10nF
GND
+VSS
VAUX SECONDARY
+
R15
C4
C19
3.01k
330 µF
10µF
+VSS
C10
100nF
R16
20k
GND
U4
R18
22.1
3
1
4
R8
GND
16.9k
R17
1k
C9
R14
220pF
1.37k
GND
SLUUAK4 – August 2013
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PIN5
12Vout
PIN7
GND
PIN6
400-V monitor
400V = 1.5V
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