Canon GP160, Service Manual

Page: 101 / 797

COPYRIGHT © 1999 CANON INC. CANON GP160 REV.0 FEB. 1999 PRINTED IN JAPAN (IMPRIME AU JAPON)
CHAPTER 6 IMAGE FORMATION SYSTEM
6-3
II. PRIMARY CHARGING ROLLER BIAS CONTROL
A. Outline
The primary charging roller bias is controlled by the DC controller PCB’s CPU
(IC301). AC bias as well as DC bias is applied to the primary charging roller in order to
stabilize the charging.
• DC bias fixed voltage control
• AC bias fixed current control
• Bias switching control
B. Control operation
The outputs of the DC bias and AC bias, which are applied to the primary charging
roller, are controlled by the DC (DCPWM) control signal and AC (PRACON) control sig-
nal respectively, which are output from the CPU (IC301). The DC bias, which is output
from the DC drive unit, is detected by the DC voltage sensor circuit, and is fed back to
the DC drive circuit via the comparison circuit. In this way, the CPU controls the primary
high-voltage DC component (constant voltage control).The AC bias output is detected
by the AC current control circuit, is fed back to the AC drive circuit via the comparison
circuit, and controlled by the CPU (constant current control).
Furthermore, the bias output to the primary charging roller of this unit changes
depending on the print resolution (1200dpi equivalent or 600dpi equivalent).
The bias output switches between the DC and AC drive circuits, in response to the
bias switching signal (1200dpi equivalent) from the CPU.
Figure 6-201
AC voltage
control
Compari-
son
Compari-
son
AC drive
DC drive
Bias switching
DC voltage
control
Primary charging roller
Photo-
sensitive
drum
CPU
(IC301)
DC controller PCB
Super-
impose
[1] PRACON
[2] 1200DPI
[3] DCPWM
JH401
[1] PRACON: AC control signal
[2] 1200DPI: Bias switching signal
[3] DCWM: DC control signal