Canon 1000 Service Manual page 144

3. OPERATION AND TIMING
4. Controlling the Pre-Primary Charging
Figure 3-524 shows the circuit that controls pre-primary charging current, and the circuit has the
following functions:
1 Turns ON/OFF the pre-primary corona current.
2 Executes constant current control.
The pre-primary corona current is turned off and on by the pre-primary corona current drive signal
(HVPPR) as follows:
Input in the range of HVPPR=0V to 12V
An output voltage suited to voltage of HVGR is generated by the transformer.
The pulse output drives the transformer.
Corona current that suits the voltage of HVPPR is generated.
The output of the pre-primary current is monitored with reference to its current value, and the data is fed
back to the variable pulse oscillator circuit. The feedback signal is used to ensure a specific level of pre-
primary corona current. If overcurrent, because of leakage for example, is detected, the pulse output is
forced off; the pre-primary corona current will remain OFF for 20 ms and thereafter will return automatically.
3-100
COPYRIGHT © 2001 CANON INC.
DC controller PCB
24V
Variable width pulse
oscillator circuit
OC
Overcurrent
detection circuit
(Correction is executed each time the Start key is pressed based on
HVPPR data from the environment sensor and the potential control.)
HVT2-1
Transformer
Current
detection
circuit
Pre-primary charging assembly
Figure 3-524
CANON CLC1000/1000S/3100 REV.2 MAY 2001 PRINTED IN JAPAN (IMPRIME AU JAPON)
Environment
sensor
Corona current