Samsung SF-830 Service Manual page 155

CIRCUIT DESCRIPTION
3-5-7-6. THV(THV(+)/THV(-) Output Unit)
Transfer(+) output unit is the transfer output control signal 'PWM-LOW ACTIVE'.
When THV-PWM LOW signal is received, Q203 turns on and the steady voltage will be accepted to the non-inverting ter-
minal of OP-AMP 324. As the voltage is higher than the inverting reference voltage of OP-AMP, OP-AMP output turns high.
The 24V power adjusts the electric potential to ZD201 and ZD202, sends IB to TRANS auxiliary wire through current-
restricting resistance R215 via R212 and C204, and eventually Q204 will turn on. When the current is accepted to Q402,
Ic increases to the current proportional to time through the T201 primary coil, and when it reaches the Hfe limit of Q204, it will
not retain the "on" state, but will turn to "off". As Q402 turns 'off', TRANS N1 will have counter-electromotive force, dis-
charge energy to the secondary coil, sends current to the load and outputs THV voltage through the high voltage output
enable, which is comprised of Regulation– circuit. The output voltage is determined by the DUTY width. Q203 switches
with PWM DUTY cycle to fluctuate the output by fluctuating the OP-AMP non-inverting end VREF electric potential, and
the
maximum is output at 0% and the minimum, at 100%.Transfer(-) output unit is THV-EA 'L' enable.
When THV-EA is 'L', Q302 turns on and the VCE electric potential of Q302 will be formed and sends IB to TRANS auxil-
iary wire through R311, C305 and VR302 via current-restricting resistance R314, and eventually Q303 will turn on. When
the current is accepted to Q303, Q303's Ic increases to the current proportional to time through the T301 primary coil, and
when it reaches the Hfe limit of Q303, it will not retain the "on" state, but will turn to "off". As Q303 turns 'off', TRANS
N1 will have counter-electromotive force, discharge energy to the secondary coil, send current to load and output THV(-)
voltage through the high voltage output enable, which is comprised of Regulation– circuit.
5V
R201
10K
U2
U2
1 2 3
#7 TEV-PWM
R206
R205
100
1.8K
Q203
A708Y
R207
24VS 2K
+ C101
35V47 F
U
#17
5V
#19
5V
5 6
TEV-EA
#5
U2
7 7407
D-GND
#24 TEV-READ
Repair Manual
3-36
18V
D201
1N4148
R208
30K
R209
100KF
C201 C202 D202
R210 R211
121
103 1N4148
VR201 845KF 1MF
50K
D301
1N4148
24VS
C4
103
10
+
8
U1
R302 R303
9
R304
_
33K 100KF
389KF
KA324
C302 C303
D302
102 103 R305
1N4148
R301
10KF
470K
VR301
5K
C301
222
24VS
5
+
7
R213
U1
2.2K
_
6 Q204
D526
11 KA324
C204
R212 C203 D203 R214
ZD201 ZD202
333Z
680K 472 1N4148
5.65V 705V 2.2K
18V
R312
R309
1W56
202K
Q301
A708Y
R307
R313
33K
1W56
18V
R310
Q303
2.2K
D526
Q302
A708Y
R308
33K
VR302
2K
R306
C305
R314
R311
26.1KF
333Z
100KF 1.7K
C304
500V103Z
T201
C206
C208
KAB-007
6KV470pF
6KV
1 7
C205
D204 D205
2KV68pF 6KV 6KV
5 6
C207
3KV470pF
2
R216 R218
MGR1/2W100KF
SBR306
4
R217
R215
SBR207
390
KAB-006
C307 D304
T301
3KW470pF 4KV
1
6
C306 D303 C308
R315
4KV
2KV68pF 3KV470pF SBR306
5
7
2
4
Samsung Electronics
D206
D207
6KV
6KV
C209
6KV