Controlling The Transfer Roller Bias - Canon NP6412 Service Manual

D.

Controlling the Transfer Roller Bias

1. Outline
The circuit shown in Figure 4-105 is used to control the voltage applied to the transfer charging
roller, and has the following functions:
• Turning on and off the transfer bias.
• Controlling the transfer bias to a constant voltage.
• Correcting the transfer bias voltage level (ATVC)
• Switching the transfer bias polarity (cleaning bias)
(Q101)
Serial
communi-
cation
DC controller PCB
COPYRIGHT © 1999 CANON INC.
Main
transformer
Transfer positive DC
bias generation circuit
T101
Transfer positive DC bias ON signal
T_REV_ON*
Transfer overcurrent detection signal
(Q900)
Transfer current detection signal
T_FW_S
Transfer bias voltage
detection signal
T_FEEDBACK
Transfer DC bias
control signal
T_FW_DRV
Transfer DC bias ON signal
T_FW_ON
High-voltage transformer
control signal
CLK32K
CANON NP6512/6612/7120/7130/7130F REV.0 AUG. 1999 PRINTED IN JAPAN (IMPRIME AU JAPON)
CHAPTER 4 IMAGE FORMATION SYSTEM
HV_LIMIT
Transfer bias
detection circuit
Transfer bias
control circuit
+24V
Composite power supply PCB
Figure 4-105
Photo-
sensitive
drum
T302
Transfer
high-voltage
transformer
Transfer
charging
roller
4-9