Canon PC300 Service Manual page 50

=. Transfer Charging Control
Circuit
i. Outline
Figure 3-20 shows the circuit that con-
trols transfer charging, and the circuit has
the following functions:
* Controls the constant current in mea-
surement mode.
* Controls the constant voltage of the
DC bias.
* Switches the polarities of the DC bias
(cleaning mode).
The internal resistance of the transfer
corona roller tends to vary from one roller to
another or because of changes in the envi-
ronment.
The copier sends constant current to the
transfer charging roller so that the micropro-
cessor can check the changes in terms of
voltage (measurement mode).
Based on the measured voltage, the
microprocessor corrects the DC bias.
Further, the copier is equipped with a
cleaning mechanism (cleaning mode) that
prevents adhesion of toner to the transfer
charging roller.
In cleaning mode while the drum is rotat-
ing, except during transfer, a DC bias is
applied to the transfer charging roller with a
reversed polarity, thereby returning the toner
to the photosensitive drum.
Transfer
(negative DC bias)
Cleaning mode
(positive DC bias)
COPYRIGHT © 1994 CANON INC. CANON PC300/320/925,FC210/200 REV.O JULY 1994 PRINTED IN JAPAN (IMPRIME AU JAPON)
<i¢ OPERATIONS AND TIMING 2a)
3-23