Canon LBP-2000 Service Manual page 60

b. Development
DC controller PCB
/DCPWM
ASIC
/DVDCUP
/DVDCFOT
/DVACFOT
/DVACON
TNRCHKD
CPU
TNRCHKT
The ASIC generates the developing AC bias drive signal (/DVACFOT), developing AC bias ON/OFF
signal (/DVACON), developing DC bias drive signal (/DVDCFOT), and primary /developing DC
bias output level signal (/DCPWM), and applies a voltage which is a combination of a developing
AC bias and a developing DC bias to the developing cylinder.
When not forming images, the developing DC bias output switch signal (/DVDCUP) is used to
apply the developing DC bias (with a voltage higher than that used when forming an image) to
prevent soiling of the pressure roller.
The developing DC bias is monitored by the developing DC bias voltage detection circuit, and is
fed back to the DC generation circuit by way of the comparison circuit so that the Printer may
control the voltage of the developing DC bias. The developing DC bias is varied in conjunction with
the voltage of the primary DC bias according to the image density data from the video controller
PCB.
To primary bias circuit
Developing bias circuit
Developing DC
Comparison
bias voltage
circuit
detection circuit
DC generation circuit
Superimposition
AC generating circuit
Developing bias
detection circuit
Toner level
detecting circuit
Figure 2-2-11
CHAPTER 2
Dv TB403/TB404
To developing
cylinder
Ant TB405/TB406
From toner level sensor
2 - 21