Read Sharp 28JW-74H (serv.man2) Service Manual online
50Hz Widescreen Colour Television – GA20 Chassis
Sharp Electronics (UK) Ltd
Technical Support
Issued June 02
Page 10
Vertical Driver
The STV9380 is a vertical deflection circuit operating in class D. Class D is a modulation method
where the output transistors work in switching mode at high frequency. The outputted square wave
signal is restored to an analogue signal by an external low pass filter. This method has a low power
dissipation comparatively to traditional amplifiers operating in class AB, eliminating the need of a
heat-sink and makes the device environmentally friendly due to it high efficiency.
Except for the output stage of this device which uses the class D modulation, the circuit operation is
similar to the one of a traditional linear vertical amplifier. A reference signal (sawtooth) has to be
applied to the circuit which can accept a differential or single ended signal. This sawtooth is amplified
and applied as a current to the deflection yoke. This current is measured by means of a low value
resistor (R523). The resulting voltage is used as a feed-back signal to guarantee the conformity of the
yoke current with the reference input signal.
The overvoltage necessary for a fast retrace is obtained with a capacitor (C513) charged by the
supply voltage. At the flyback moment this capacitor is connected in series with the output stage
power supply. This method avoids the need of an additional power supply for the flyback period
C514
470pF
R520
10k
C515
470pF
C516
0.1uF
IC502
SY9380
+v
cc
ea
ou
t
-vc
c
c
-vc
c
c
-vc
c
c
-v
cc
-vc
c
c
-vc
c
c
ou
t
cf
lb
+
cf
lb
-
bo
ot
vre
g
g
Fe
ed
ed
Ca
p
p
Fr
eq
in
+
in
-
gn
d
-vc
c
c
11
20
12
13
14
16 15
17
18
19
1
10
9
8
7
6
5
4
3
2
C517
0.22uF
C513
100uF
R522
1k
D1005
c4v7
+14v
-14v
-14v
L504
C519
560pF
Vertical
Scan Coils
Vprot
Vertical Drive
From IC1001
+v
cc
R519
68k
C521
100pF
R524
150
R525
220
R518
6k8
R523
0R56
0R56
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