Feed-Back Circuit - BenQ G2420HD Product Service Manual

Feed-back Circuit

IC801
9
NDR1
10
PDR1
11
VDDA
12
TIMER
13
PWM
14
ISEN
15
OVPT
16
ENA
C814 R827
0.033U K 365 F
Fig. 2 shows the feedback circuit consists of a lamp, R816, D805, R827 and C814.
With the lamp current through D805, a half sine-waveform voltage signal is produced.
We may get the Maximum value through R827/C814.
After OZ9933 gets the feedback voltage signal from PIN14, the duty of the full-bridge
driver outputs is decided.
F1
T 801
.
6 5
.
3 4
F3
.
7 8
8
NDR2
C821-2
.
7
GNDP
2 1
6
PDR2
C822
5 470P J
GNDA
4
RT1
3
CT
2
SST/CMP
1
VSEN
- 68 -
C815
100P J
C819
5PF D
R819
100K
C831
C820
0.22U K
470P J
R820
20K F
C816
100P J
C821
5PF D
R821
100K
R816
2.2K
R822
20K F
D805
BAV99
K A
Fig. 2
R815
2.2K
D809
LL4148
K A K
D801
R831
R834
BAV99
511 F
1M
TP801
CN801
1
1
TP802
2
2
2K62272102
A
TP803
CN802
1
1
TP804
2
2
2K62272102