Canon PC720 Service Manual - Page 70

transformer/rectifier

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=OPERATIONS AND TIMING 2. Turning On and Off the Transfer Roller Bias The microprocessor on the DC controller PCB sends the transfer bias on signal to the microprocessor on the composite power supply PCB. In response, the microprocessor on the composite power supply generates the transfer bias on signal to drive the transformer (T302), thereby supplying the transfer charging roller with transfer bias. 3. Controlling the Transfer Bias to a Specific Voltage The transfer bias is controlled to a spe- cific voltage by the microprocessor on the composite power supply PCB. The microprocessor on the composite power supply PCB monitors the voltage of the transfer bias at all times. The microprocessor on the composite power supply PCB sends the transfer bias control signal through the pulse/DC conversion circuit according to the detected voltage to the voltage control circuit to maintain the transfer bias to a specific voltage. 4. Correcting the Voltage Level of the Transfer Bias The copier corrects the voltage level of the transfer bias in any of the following two ways: • before starting copying (ATVC) • after starting copying a. Before Starting Copying (ATVC) To correct changes in the transfer effi- ciency caused by changes in the environment or deterioration of the transfer roller, the copier automatically corrects the application voltage level of the transfer bias. During initial rotation after the Copy Start key is pressed, the copier feeds a specific current to the transfer roller. The current detection circuit on the composite power supply PCB sends measurements of the current to the microprocessor in the form of the current detection signal. The microprocessor determines the voltage to be applied to the transfer roller based on such data. This control is executed once during initial rotation after a press on the Copy Start key. b. After Starting Copying The copier automatically corrects the application voltage during copying operation to compensate for the changes in the transfer efficiency caused by different types of copy paper. The current detection circuit detects the current flowing through the transfer charging roller and sends the data to the microprocessor on the composite power supply PCB. Using the data, the microprocessor determines the voltage to be applied to the transfer charging roller and controls the DC bias voltage by generating the transfer DC bias control signal so that the voltage will be optimum. 5. Switching the Polarity of the DC Bias (cleaning) The microprocessor on the DC controller PCB sends the transfer bias switching timing signal to the microprocessor on the composite power supply PCB. The microprocessor on the composite power supply PCB, on the other hand, turns off the transfer DC bias on signal and, at the same time, sends the transfer positive DC bias on signal to the positive bias control circuit. The voltage from the positive bias control circuit is sent to the transfer charging roller through the transformer/rectifier circuit. 3 - 30 COPYRIGHT © 1994 CANON CANON PC72011401150= RBA AUG.1994 PRINTED IN JAPAN (IMPRNE AU JAPONI

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=OPERATIONS
AND
TIMING
2.
Turning
On
and
Off
the
Transfer
Roller
Bias
The
microprocessor
on
the
DC
controller
PCB
sends
the
transfer
bias
on
signal
to
the
microprocessor
on
the
composite
power
supply
PCB.
In
response,
the
microproces-
sor
on
the
composite
power
supply
gener-
ates
the
transfer
bias
on
signal
to
drive
the
transformer
(T302),
thereby
supplying
the
transfer
charging
roller
with
transfer
bias.
3.
Controlling
the
Transfer
Bias
to
a
Specific
Voltage
The
transfer
bias
is
controlled
to
a
spe-
cific
voltage
by
the
microprocessor
on
the
composite
power
supply
PCB.
The
micropro-
cessor
on
the
composite
power
supply
PCB
monitors
the
voltage
of
the
transfer
bias
at
all
times.
The
microprocessor
on
the
com-
posite
power
supply
PCB
sends
the
transfer
bias
control
signal
through
the
pulse/DC
conversion
circuit
according
to
the
detected
voltage
to
the
voltage
control
circuit
to
main-
tain
the
transfer
bias
to
a
specific
voltage.
4.
Correcting
the
Voltage
Level
of
the
Transfer
Bias
The
copier
corrects
the
voltage
level
of
the
transfer
bias
in
any
of
the
following
two
ways:
•
before
starting
copying
(ATVC)
•
after
starting
copying
a.
Before
Starting
Copying
(ATVC)
To
correct
changes
in
the
transfer
effi-
ciency
caused
by
changes
in
the
environ-
ment
or
deterioration
of
the
transfer
roller,
the
copier
automatically
corrects the
applica-
tion
voltage
level
of
the
transfer
bias.
During
initial
rotation
after
the
Copy
Start
key
is
pressed,
the
copier
feeds
a
specific
current
to
the
transfer
roller.
The
current
detection
circuit
on
the
composite
power
supply
PCB
sends
measurements
of
the
cur-
rent
to
the
microprocessor
in
the
form
of
the
current
detection
signal.
The
microprocessor
determines
the
voltage
to
be
applied
to
the
transfer
roller
based
on
such
data.
This
control
is
executed
once
during
ini-
tial
rotation
after
a
press
on
the
Copy
Start
key.
b.
After
Starting
Copying
The
copier
automatically
corrects
the
application
voltage
during
copying
operation
to
compensate
for
the
changes
in
the
trans-
fer
efficiency
caused
by
different
types
of
copy
paper.
The
current
detection
circuit
detects
the
current
flowing
through
the
transfer
charging
roller
and
sends
the
data
to
the
microproces-
sor
on
the
composite
power
supply
PCB.
Using
the
data,
the
microprocessor
deter-
mines
the
voltage
to
be
applied
to
the
trans-
fer
charging
roller
and
controls
the
DC
bias
voltage
by
generating
the
transfer
DC
bias
control
signal
so
that
the
voltage
will
be
opti-
mum.
5.
Switching
the
Polarity
of
the
DC
Bias
(cleaning)
The
microprocessor
on
the
DC
controller
PCB
sends
the
transfer
bias
switching
timing
signal
to
the
microprocessor
on
the
compos-
ite
power
supply
PCB.
The
microprocessor
on
the
composite
power
supply
PCB,
on
the
other
hand,
turns
off
the
transfer
DC
bias
on
signal
and,
at
the
same
time,
sends
the
transfer
positive
DC
bias
on
signal
to
the
positive
bias
control
cir-
cuit.
The
voltage
from
the
positive
bias
con-
trol
circuit
is
sent
to
the
transfer
charging
roller
through
the
transformer/rectifier
circuit.
3
-
30
COPYRIGHT
©
1994
CANON
CANON
PC72011401150=
RBA
AUG.1994
PRINTED
IN
JAPAN
(IMPRNE
AU
JAPONI