Canon 1000S, Service Manual

Page: 167 / 840

COPYRIGHT © 2001 CANON INC. CANON CLC1000/1000S/3100 REV.2 MAY 2001 PRINTED IN JAPAN (IMPRIME AU JAPON)
3-123
3. OPERATION AND TIMING
2. Controlling the Transfer Current
Figure 3-555 shows the circuit that controls the transfer current, and the circuit has the following
functions:
• Turns on and off the transfer current.
• Controls the transfer current.
Figure 3-555
The transfer current is turned on and off by the transfer current drive signal (HVT-Y, HVT-M, HVT-C,
HVT-Bk) as follows:
Input in the range of HVTR-Y=0V to 12V
Q1 turns on, and a drive voltage suited to the voltage level of HVTR-Y is sent to the transformer.
The transformer is driven, and transfer current is generated.
The output of transfer current is monitored by its current value, and the data is fed back to the transistor
Q1. The feedback signal is used to control the transformer drive voltage, thereby maintaining the transfer
current at a specific level.
If an abnormally high voltage occurs, because of passage of the edge of paper for example, and
overcurrent is detected, the OC signal forces Q1 OFF to stop the supply of the transformer drive voltage for
20 msec; the supply will return automatically thereafter.
Further, with the help of the environment sensor, the current value is corrected each time the Start key
is pressed.
DC controller
Transfer blade
HVT1
Pulse oscillator circuit
24V
Overcurrent
detection circuit
Current
detection circuit
Transformer
Environment
sensor
Q1
Q2
Transfer current
Feedback
OC
HVTR-Y
24V