Canon LBP3250 Series, Service Manual, Page: 32 / 98

Chapter 2
2-13
2.4.2 High-Voltage Control
2.4.2.1 Overview
0019-9522
This circuit is comprised of the circuits that apply biases to the primary charging roller, developing cylinder, transfer roller, and the fixing control circuit. The CPU
of the engine controller controls the high-voltage power supply circuit to generate these biases. The fixing control circuit executes heater control of the fixing as-
sembly according to the instruction by the CPU of the engine controller.
The following is the block diagram of this circuit.
F-2-15
2.4.2.2 Generating Primary Charging Bias
0019-9523
The primary charging bias (PRI) is a DC negative bias that is output to apply an even negative potential to the surface of the photosensitive drum. The primary
charging high-voltage generating circuit in the high-voltage power supply circuit generates this bias.
The high-voltage power supply circuit applies the generated primary charging bias to the primary charging roller at a specified timing.
The primary charging bias varies in conjunction with the developing bias according to the information of image density sent from the main controller.
2.4.2.3 Generating Developing Bias
0019-9524
The developing bias is a DC negative bias that is output to affix toner to the static latent images formed on the photosensitive drum. This bias is a development DC
and AC superimposed bias and generated by the development high-voltage generating circuit in the high-voltage power supply circuit.
The high-voltage power supply circuit applies the generated developing bias to the developing cylinder at a specified timing.
The developing bias varies in conjunction with the primary charging bias according to the information of image density sent from the main controller.
2.4.2.4 Generating Transfer Bias
0019-9525
Transfer bias (TR) is a bias that is output to transfer toner to papers. There are two types of bias; DC positive bias and DC negative bias, and generated by the transfer
high-voltage generating circuit in the high-voltage power supply circuit. The DC positive bias is output at the time of toner transfer, and the DC negative bias at the
time of cleaning the photosensitive drum.
The high-voltage power supply circuit applies the generated transfer bias to the transfer roller according to each print sequence.
Each print sequence is described below.
- Cleaning bias:
The bias to move (clean) the toner attached to the transfer roller to the photosensitive drum at the time of warming up or last rotation sequence.
The transfer negative bias is applied to the transfer roller.
- Paper intervals bias:
The bias to prevent the toner remained on the photosensitive drum from attaching to the transfer roller at paper intervals during continuous printing. A minor
transfer positive bias is applied to the transfer roller.
- Print bias:
The bias to transfer the toner on the surface of the photosensitive drum to papers at the time of print sequence. The transfer positive bias is applied to the transfer
roller.
Transfer roller
CPU
High-voltage power supply
Primary
charging
high-voltage
generation
circuit
Developing
high-voltage
generation
circuit
Transfer
high-voltage
generation
circuit
primary charging roller
developing cylinder
Engine controller
PRI
DEV
TR