Canon NP6412 Service Manual page 98

CHAPTER 4 IMAGE FORMATION SYSTEM
2. Operations
a. Turning On and Off the DC Bias
The DC bias applied to the primary charging roller is turned on or off by the serial communica-
tion signal and the primary charging bias ON signal (PR_DC_ON) from the DC controller PCB.
When the Copy Start key is pressed, the DC bias ON signal (serial) and the primary charging
bias ON signal (PR_DC_ON) are sent. The microprocessor (Q900) on the composite power supply
PCB generates the DC bias control signal (PDC_PWM) based on the combination of the serial
signal and the PR_DC_ON signal, applying a DC bias to the primary charging roller.
DC bias ON
(image area)
DC bias ON
(non-image area)
DC bias ON
(non-image area)
DC bias ON
(APVC)
DC bias OFF
*1: Area between sheets
*2: Cleaning area by transfer / trailing edge area
Table 4-102 Relationship between DC Bias Output and Signal
b. Controlling the DC Bias to a Specific Voltage/Current
The DC bias applied to the primary charging roller is controlled by the microprocessor (Q900)
on the composite power supply PCB so that it remains a specific level.
When a DC bias is generated, the microprocessor (Q900) on the composite power supply PCB
detects the DC voltage monitor signal (PDC_S), compares its level against the reference level, and
varies the DC bias control signal (PDC_PWM) according to the difference so as to ensure that it
remains specific level.
Reference:
The DC bias control signal varies its pulse duty ratio to change the level of the DC bias.
4-6
COPYRIGHT © 1999 CANON INC.
DC bias ON signal
(8-bit signal communication)
bit0
1
1
*1
1
*2
0
0
CANON NP6512/6612/7120/7130/7130F REV.0 AUG. 1999 PRINTED IN JAPAN (IMPRIME AU JAPON)
PR_DC_ON
(J103-5)
bit1
– 0
0 1
1 1
– 0
0 1