Canon PC720 Service Manual - Page 69

Microprocessor

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I OPERATIONS AND TIMING Figure 3-315 shows the circuit that controls the foregoing three types of bias, and the circuit has the following functions: • turns on and off the transfer roller bias. • controls the transfer bias to a constant voltage. • corrects the voltage level of the transfer bias (ATVC) - switches the polarity of the DC bias (cleaning). Transfer Photosensitive charging drum roller former 1302 +24V tl Voltage77-/control circuit Trans ormer T 0 Positive bias control circuit A 0 ciliation circuit 0 Transformer/ rectifier circuit Constant current control circuit Current detection - circuit Ca Io-n "c7r er DC bias sian .6"" C.) O >0 w 0 IC-C o0n1 0. (15 uc ) C EIL c 1- 0 I- Pulse/DC cone sion circuit o or >cc u) 2 -(S C Microprocessor Current limiter circuit a Composite power supply PCB U 0 0 -2 Oo "1-7, O E 1P-2 C0..00.1,.E Microprocessor DC control PCB Figure 3-315 COPYRIGHT © 1994 CANONINC. CANON PC72017401T50/770 REV.0 AUG.1994 PRINTED IN JAPAN (IMPRIME AU JAPON) 3 - 29

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I
OPERATIONS
AND
TIMING
Figure
3-315
shows
the
circuit
that
controls
the
foregoing
three
types
of
bias,
and
the
circuit
has
the
following
functions:
•
turns
on
and
off
the
transfer
roller
bias.
•
controls
the
transfer
bias
to
a
constant
voltage.
•
corrects
the
voltage
level
of
the
transfer
bias
(ATVC)
-
switches
the
polarity
of
the
DC
bias
(cleaning).
Photosensitive
drum
Transfer
charging
roller
Trans
ormer
T
0
Positive
bias
control
circuit
A
Ca
C.)
O
0
>
w
CC
0
I-
0.
(15
u)
c
EL
I c
1—
0
"c7r
.
6""
01
on
former
1302
0
cil-
iation
circuit
+24V
tl
Voltage
77-/-
control
circuit
0
I—
on
er
DC
bias
sian
C
I
—
Transformer/
rectifier
circuit
Constant
current
control
circuit
Pulse/DC
cone
sion
circuit
o
or
>
cc
u)
2
(S
—
C
Current
detection
—
circuit
Current
limiter
circuit
a
Microprocessor
Composite
power
supply
PCB
U
—
o
0
0
2
O
"1-7,
O
E
P2
C
0,
1-
0..0
1
..E
Microprocessor
DC
control
PCB
Figure
3-315
COPYRIGHT
©
1994
CANON
INC.
CANON
PC72017401T50/770
REV.0
AUG.1994
PRINTED
IN
JAPAN
(IMPRIME
AU
JAPON)
3
-
29