Xerox Phaser 3450 Service Manual page 152

11.4 High Pressure Printing
11.4.1 MHV (Electric Charge Printing Section)
Charging output of ENABLE is 'MHV-PWM LOW ACTIVE', which is charging output controlling signal. When MHV-PWM
signal is applied, regular voltage flows to OP-AMP non-inverting terminal via filter R401, C401, R402, and C402. It
becomes HIGH or LOW in comparison with feedback voltage which flows to OP-AMP inverting terminal. If OP-AMP output
becomes high, Q401 turns off, and voltage of 24V1 flows normally to base unit of Q404, switching TR, and it turns on.
After voltage flows to Q404, IC passes the first T401, and it increases as voltage, which is proportionate to time. When this
voltage reaches to the HFE critical point of Q404, 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 MHV voltage via high voltage output unit
consisted of rectifier circuit.
When OP-AMP output becomes low, Q401 and Q403 turn on. At this time, base voltage of Q404 becomes GND voltage
and Q404 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.
5V1
5V1
D401
R400
1N4148
5.6K
MHV-sen >>
MHV PWM
CN1-#6
13 12
MHV
R401 R402
IC103/F
47K 22K
7407
C401 C402 D402
473 102 1N4148
R461
RD1/8W2.2KJ RS1/8W30KF
MHV_READ
MHV READ
CN1-#10
C456
MY2A473
ZD404
3.3B
C404 R403
472 1.5M
R409
5.6K
5
+
Q401
7
A708-Y
6
-
R404
10K
R408
10K
C403
331 C458
Q403
MY2A473
C945C-Y
MHV_READ
R458
50K
IC104/D
12
+
14
13
-
R460
RD1/8W1.5K KA324
24V1
ZD401 C406
2.7V R410 CE-103
100K
T401
4
R411 C405
470 104
2
5
C407
103
1
Q404
C2316
ZD402 R412 D403
2.7VB 1/4W4.7J D1NL20U
D455
1N4148
C457
CE-103 D456
1N4148
CIRCUIT DESCRIPTION
D404 R450 R415
4KV MGR1/4W560KJ RDS1/2W100K
R416
R414
C409 BLR1/2W100MJ
BLR1/2W60MF
6
3KV471
7
>>MHV-sen
5V1
ZD403
R417
100V
100J
R413 C459
30KF C-CE221
5V1
MHV
20K
C460
47uF
C410
CE-104
Service Manual
>> MHV
>> OPC
11-21