Canon NP6012 Service Manual page 69

2. Operation
a. Turning On and Off the DC Bias
When the Copy Start key is pressed, the
microprocessor on the DC controller PCB
instructs the microprocessor on the compos-
ite power supply PCB to turn on the DC bias.
The microprocessor on the composite
power supply PCB drives the main trans-
former (T102).
The DC bias is generated by rectifying
the voltage from the main transformer
(7102) and is sent to the primary charging
roller.
b. Controlling the DC Bias to a Specific
Voltage
The DC bias is controlled to a specific
voltage by the microprocessor on the com-
posite power supply PCB. The microproces-
sor on the composite power supply PCB
constantly monitors the DC voltage. The
microprocessor serves to maintain the DC
bias voltage to a constant value by varying
the DC bias control signal (PDCPWM)
based on measurements of voltage taken.
c. Switching the DC Bias Voltage Level!
The copier switches the level of the DC
bias voltage according to whether or not
copy images are being formed.
The DC bias voltage is switched by the
microprocessor on the composite power
supply PCB by varying the DC bias control
signal (PDCPWM) according to the DC bias
switching timing signal sent by the micropro-
cessor on the DC controller PCB.
during copying: -900 V
other: -1376 V
Copy Start key
ON
Main motor (M1)
Sra [TA [Sew [SRN] (SiR
Scanning lamp (FL1)
Primary charging roller DC bias
a a
SS
SYLLLA
a
Figure 3-308
3-24 COPYRIGHT © 1995 CANON INC.
CANON NP6C12/NP5012F/NP6212 REV SEPT. 1996 PRINTED IN JAPAN (IMPRIME AU JAPON)