Xerox Phaser 3450 Service Manual page 154

11.4.3 THV(THV(+) / THV(-) Section)
Transfer (+) output enable is 'THV-PWMLOW ACTIVE', transfer output controlling signal.
When THV-PWMLOW signal is applied, Q201 turns on, and regular voltage flows to OP-AMP non-inverting terminal via
filter R;204 C201, R205, and C202. It becomes HIGH or LOW in comparison with feedback voltage which flows to OP-
AMP inverting terminal. If OP-AMP output becomes high, Q202 turns off, and voltage of 24V1 flows normally to base unit
of Q203, switching TR, and it turns on.
After voltage flows to Q203, IC passes the first T201, and after passing coil, it is increased as voltage that is proportionate
to time. When this voltage reaches to the HFE critical point of Q203 it turns off. At this time, counter electromotive force is
created on trans 1 by turn-off action, and energy is emitted to trans 2 to send voltage to output THV voltage (+) via high
voltage output unit consisted of rectifier circuit.
When OP-AMP output becomes low, Q202 turns on. At this time, base voltage of Q203 becomes GND voltage and Q203
turns off to prevent to create high voltage.
Charging circuit detects changes due to environment of charging roller, and applies proper voltage to OPC for each
environment. The environment changes (resistance) are detected by comparator, and comparator converts analog input
to digital output.
Depending on such digital output, program inputted in ROM of engine controller applies proper charging voltage for each
environment in consideration of resistance changes.
Transfer (-) output enable is 'THV- EA HIGH ACTIVE', transfer output controlling signal.
When THV-EA HIGH SIGNAL is applied, Q300 turns off and voltage of 24V1 flows normally to base unite of Q302,
switching TR, for turn-on.
After voltage flows to Q302, IC passes the coil of first T301, and after passing coil, it is increased as voltage that is
proportionate to time. When this voltage reaches to the HFE critical point of Q203, it becomes off. At this time, counter
electromotive force is created on trans 1 by turn-off action of Q302, and energy is emitted to trans 2 to send voltage to
output THV voltage (-) via high voltage output unit consisted of rectifier circuit.
When THV-EA LOW signal is applied, Q300 and Q301 turn on. Base voltage of Q302 becomes ground voltage, and it is
turned off to prevent to create high voltage.
5V1
R203
100
Q201
THV
A708-Y
R202 D201
430 1N4148
THV-sen >>
R204 R205
47K 22K
R201
2K C201
C202
473
102
5V1
R300
100
THV -EA
CN1-#14
THV
R301
430
C306
MY2A473J
INDEX
50K
R308
THV READ
1.5K
CN1-#12
7
THV_READ
C307 IC105/B
473
ZD302
3.3B
5V1
C204
CE-103
IC105/A
KA358
3
+
Q202
1
945C-Y
2
-
R208
10K
THV
50K
C203 R207
C205
681 330KF
R206 471
16.2KF
ZD201
2.7VB
R302
470K
Q300
A708-Y
Q301
R310
945C-Y
1K
R311
2.2k
ZD301
+5V1
2.7VB
R307
330KF
D305
1N4148
5
+
6
-
24V1
C207
R209 CE-103
100K
T201
4
R210 C206
5.6KJ 104
2
5 6
1 7
Q203
C208
C2383 D203
681
D1NL20U
D202
D1NL20U
C213
221
R211
24V1
1/4W4.7J
C302
CE-103
T301
4
R303
C301
470
104
2
C303
5 6
103
1 7
Q302
C2383
D301
D1NL20U
R304
1/4W4.7
CIRCUIT DESCRIPTION
C209
6KV221
C211
6KV221
D205 D206
D204 6KV 6KV
6KV C210
>> THV
6KV221
R212
RDS1/2W100K
VA201
R213
7D431K
BLR1/2W30MF
VA202
7D431K
D302
4KV
R305
C304
BLR1/2W50MF
3KV151
>> THV-sen
R306
100KF
D303
1N4148
D304 C305
1N4148 CE-104
Service Manual
11-23