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Chapter 2

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The primary charging bias circuit generates the negative DC voltage and AC voltage. They are superimposed and applied to the primary charging roller. The circuit

also applies the negative DC voltage to the fixing film unit through the pressure roller. In addition, this circuit detects the presence of cartridge.

The developing bias circuit generates negative DC voltage and AC voltage. They are superimposed and applied to the developing cylinder.

The transfer charging bias circuit generates positive or negative DC voltage and applies the positive or negative DC voltage to the transfer charging roller.

These circuits are controlled by the commands from the CPU (IC201) on the engine controller.

The following section describes each generation circuit.

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2.4.2.2 Primary charging bias generation

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The primary charging bias (PR) is generated according to two signals output from the CPU: the PRIMARY CHARGING DC BIAS DRIVE signal (PRDCC) and

the PRIMARY CHARGING AC BIAS DRIVE signal (PRACC).

The PRDCC signal is a clock signal to generate the DC bias and the primary charging DC bias is generated according to this signal. The PRACC signal is a clock

signal to generate the AC bias and the primary charging AC bias is generated according to this signal. The superimposed voltage of primary charging AC and the

primary charging DC biases is applied to the primary charging roller.

The primary DC bias changes with the developing DC bias in response to the image density information sent from the video controller.

2.4.2.3 Developing bias generation

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The developing bias (DV) is generated according to the DEVELOPING AC BIAS DRIVE signal (DVACC) output from the CPU.

The DVACC signal is a clock signal to generate the AC bias and the developing AC bias is generated according to this signal. The developing DC bias is generated

according to the developing AC bias generated in the developing AC bias generation circuit. The superimposed voltage

of the developing DC bias and the developing AC bias is applied to the developing cylinder.

The developing DC bias changes with the primary charging DC bias, in response to the image density information sent from the video controller.

2.4.2.4 Transfer charging bias generation

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The transfer bias (TR) is generated by three signals output from the CPU: the TRANSFER POSITIVE BIAS DRIVE signal (TRPFOT), the TRANSFER NEGA-

TIVE BIAS DRIVE signal (TRNFOT), and the TRANSFER OUTPUT SWITCHING signal (TRPWM).

The TRPFOT signal is a clock signal to generate the positive bias and the transfer positive bias is generated according to this signal. The TRNFOT signal is a clock

signal to generate the negative bias and the transfer negative bias is generated according to this signal. The voltage of either the transfer positive bias or the transfer

Developing cylinder

Photosensitive drum

Primary charging roller

Transfer charging roller

Pressure roller

Fixing film unit

IC201

CPU

DVACC

TRNFOT

TRCRNT

TRPFOT