Xerox Phaser 3450, Service Manual, Page: 154 / 155

11-23
CIRCUIT DESCRIPTION
Service Manual
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.
R302
470K C302
CE-103
R213
BLR1/2W30MF
R208
10K
ZD201
2.7VB
Q203
C2383
D202
D1NL20U
D203
D1NL20U
ZD301
2.7VB
D301
D1NL20U
Q302
C2383
C304
3KV151
R305
BLR1/2W50MF
C305
CE-104 D304
1N4148
Q202
945C-Y
C208
681
R212
RDS1/2W100K
D303
1N4148
D302
4KV
24V1
24V1
INDEX
50K
C207
CE-103
R209
100K
5V1
D201
1N4148
C204
CE-103
R205
22K
C202
102
T301
C206
104
THV
50K
R206
16.2KF
C203
681
T201
C301
104
R304
1/4W4.7
C306
MY2A473J
D305
1N4148
R307
330KF
+
5
-
6
7
IC105/B
5V1
R203
100
R202
430
Q201
A708-Y
R300
100
R301
430
Q300
A708-Y
R211
1/4W4.7J
Q301
945C-Y
+
3
-
2
1
11
4
IC105/A
KA358
R210
5.6KJ
5V1
R311
2.2k
R310
1K
D204
6KV C210
6KV221
C211
6KV221
C209
6KV221
D205
6KV D206
6KV
C205
471
R207
330KF
C307
473
ZD302
3.3B
VA201
7D431K
VA202
7D431K
C213
221
C303
103
R308
1.5K
C201
473
R303
470
R306
100KF
R201
2K
R204
47K
THV_READ
THV
THV
>> THV-sen
THV READ
CN1-#12
>> THV
>> THV-sen
4
2
5
1
4
2
5
1
6
7
+5V1
CN1-#14
THV -EA
7
6