Xerox WorkCentre M20 Service Manual page 260

BIAS (Supply/Dev/Blade Output Unit)
BIAS (Electrification Output Enable) Electrification Output Enable is the electrification output
control signal 'PWM-LOW ACTIVE'.When BIAS-PWM LOW signal is received, Q501 turns on
and the steady voltage will be accepted to the non-inverting terminal of OP-AMP 324. As the
voltage higher than the inverting reference voltage of OP-AMP, which is set to R506 and R507,
OP-AMP output turns high. This output sends IB to the TRANS auxiliary wire through cur-
rent-restricting resistance Q502 via R509 and C504 and Q502 turns on. When the current is
accepted to Q502, Ic increases to the current proportional to time through the T201 primary
coil, and when it reaches the Hfe limit of Q502, it will not retain the "on" state, but will turn to
"off". As Q502 turns 'off', TRANS N1
energy to the secondary unit, sends current to the load and outputs DEV voltage through the
high voltage output enable, which is comprised of Regulation-circuit. Refer to Figure 7.
Figure 7 Bias signal
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 terminal 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 auxil-
iary wire through current-restricting resistance
Q204 will turn on. When the current is accepted to Q402, Ic increases to the current propor-
tional 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
counter-electromotive force, discharge energy to the secondary coil, sends current to the load
and outputs THV voltage through the high voltage output enable, which is comprised of Reg-
ulation– 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(-) out-
put unit is THV-EA 'L' enable.
General Procedures and Information
GP 16
will have counter-electromotive force, discharge
R215 via R212 and C204, and eventually
N1 will have
December 2006
When THV-EA is 'L', Q302 turns on and the VCE electric potential of Q302 will be formed and
sends IB to TRANS auxiliary wire through R311, C305 and VR302 via current-restricting resis-
tance 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 second-
ary coil, send current to load and output THV(-) voltage through the high voltage output enable,
which is comprised of Regulation-circuit. Refer to Figure 8.
Figure 8 THV signal
Environment Recognition
THV voltage recognizes changes in transfer roller environment and allows the voltage suitable
for the environment in order to realize optimum image output. The analog input is converted to
digital output by the comparator that recognizes the environmental changes of the transfer
roller. It is to allow the right transfer voltage to perform appropriate environmental response
considering the environment and the type of paper depending on this digital output by the pro-
grams that can be input to the engine controller ROM.
This environment recognition setting is organized as follows: First, set the THV(+) standard
voltage. Allow 200M load to transfer output, enable output and set the standard voltage 800V
using VR201. Then set 56 (CPU's recognition index value) as the standard using VR302. This
standard value with CPU makes sure that the current feedback is 4A when output voltage is
800V and load is 200M. If the load shows different resistance value when 800V is output, the
current feedback will also be different and thus the index value will also be different. according
to the index value read by CPU, the transfer voltage output will differ according to the preset
transfer table.
The changes in transfer output required by each load is controlled by PWM-DUTY.
6-54 WorkCentre M20, 4118, FaxCentre 2218 Family