Canon LBP-2000 Service Manual page 59

CHAPTER 2
2 . Operation
a . Primary charging
DC controller PCB
/DCPWM
ASIC
/PRDCFOT
/PRACFOT
/PRACON
CPU
The ASIC generates the primary AC bias drive signal (/PRACFOT), the primary AC bias ON/OFF
signal (/PRACON), the primary DC bias drive signal (/PRDCFOT), and the primary/developing DC
bias output level signal (/DCPWM); it also applies a voltage which is a combination of a primary AC
bias and a primary DC bias to the primary charging roller.
The primary AC bias is detected by the primary AC bias current detection circuit, and is fed
back to the AC generation circuit by way of the comparison circuit, thereby controlling the current
of the primary charging bias.
The primary DC bias is detected by the primary DC bias voltage detection circuit, and is fed
back to the DC generation circuit by way of the comparison circuit, thereby controlling the voltage
of the primary DC bias. The voltage of the primary DC bias is varied in conjunction with the
voltage of the developing DC bias according to the image data from the video controller PCB.
2 - 20
Primary bias circuit
Primary DC bias
Comparison
voltage detection
circuit
circuit
DC
generation circuit
Combination
AC
generation circuit
Primary AC bias
Comparison
current detection
circuit
circuit
To developing bias circuit
Figure 2-2-10
Pr TB401/TB402
To primary
charging roller