Keeping The Primary/Transfer Corona Current At A Specific Level - Canon NP6330 Service Manual

3. Keeping the Primary/Transfer Corona Current at a Specific Level

If an excess (or inadequate) corona current flows from the primary charging
assembly or the transfer charging assembly because of changes in the environment, the
level of the return current to the current control circuit will be higher (lower).
In such cases, the current control circuit controls the primary/transfer drive circuit so
that the current on the secondary side of the respective high-voltage transformer will be
smaller (larger). At the same time, the return voltage on the secondary side is introduced
to the voltage control circuit to control the primary/transfer drive circuit, thereby keeping
the primary side voltage constant.
As shown in Figure 4-105, the shielding plate of the primary charging assembly
receives the corona current generated by the primary corona wire. The high-voltage
power supply PCB (HVT) monitors the level of this current at all times; if it finds it to be
different from the standard value (-1.2 kV), the primary/transfer drive circuit starts to
control the primary corona current so that the current remains at a specific level at all
times.
Primary corona
wire
Grid
COPYRIGHT © 1997 CANON INC.
Photosensitive drum
Figure 4-105
CANON NP6330 REV.0 MAY 1997 PRINTED IN JAPAN (IMPRIME AU JAPON)
CHAPTER 4 IMAGE FORMATION SYSTEM
HVT
AC Drive circuite
R123~R125 R104
Current control circuit
1200V
constant
4-7