Canon 1000 Service Manual page 143

3. Controlling the Grid Bias
Figure 3-523 shows the circuit that controls the grid bias, and the circuit has the following functions:
1.Controls the voltage.
2.Detects overcurrent.
The grid bias is controlled by the grid bias control signal (HVGR) as follows:
Input in the range of HVGR=0V to 12V
An output voltage suited to voltage of HVGR is generated by the transformer.
The changes in the grid bias generated to suit
the grid bias control signal (HVG) are as shown in
Figure 3-522.
The output of the grid bias is monitored with reference to its voltage, and the data is fed back to the
current control circuit. The feedback signal is used to ensure a specific level of grid bias. If an overcurrent is
detected, because of leakage for example, the OC signal will turn on Q1, thereby forcing off the pulse output.
When such occurs, the grid bias will remain off for 20 ms and then will return automatically.
Pulse oscillator circuit
COPYRIGHT © 2001 CANON INC.
(Correction is executed each time the Start key is pressed based on
HVGR data from the enviroment sensor and the potential control.)
A specific voltage is applied to the grid.
DC controller PCB
24V
OC
Overcurrent
Q1
detection circuit
Voltage
detection circuit
Figure 3-523
CANON CLC1000/1000S/3100 REV.2 MAY 2001 PRINTED IN JAPAN (IMPRIME AU JAPON)
12V
11V
0V
-200V
Figure 3-522
HVT2-1
Transformer
Current
control circuit
3. OPERATION AND TIMING
-950V
Grid bias
Potential sensor
Environment sensor
Grid bias
Grid
3-99