Canon FY8-13EX-000, NP6218 service manual Controlling the Development Bias, Mpwm

CHAPTER 4 IMAGE FORMATION SYSTEM

C. Controlling the Development Bias

1. Outline

Figure 4-204 shows the circuit used to control the development bias; the circuit has the following functions:

•turns on and off the AC component of the development bias

•turns on and off the DC component of the development bias

•controls the voltage level of the DC component of the development bias

•controls the DC component of the development bias to a constant level

2.Turning On and Off the DC Component of the Developing Bias and Controlling the Voltage to a Constant Level

The microprocessor (Q512) on the composite power supply PCB generates the

BPWM signal (pulse signal) under the control of the microprocessor master (Q301) on the DC controller PCB. In response, the secondary side of the main transformer (T101) turns on to apply the DC component of the development bias.

In addition, while the DC component of the development bias is being applied, the application voltage is taken in from the development DC bias voltage detection circuit in the form of the BIASS signal (analog signal) to exert control so that the output voltage is maintained at a constant level.

The main transformer (T101) is driven by the drive signal (MPWM) from the microprocessor (Q512). In addition to the foregoing functions, the main transformer (T101) is also used as the high-voltage transformer for the DC power supply and other loads.

Composite power supply PCB
Main transformer
T101	Development
	DC bias drive	Development AC bias
	circuit
		transformer
	Development	T301			Photosensitive
	DC bias voltage	Development			drum
	detection circuit
		AC transformer
		drive circuit		ACBIAS	Developing cylinder
		BPWM
Transformer (T101)	BIASS	Microprocessor
		(Q512)
drive circuit
	MPWM
			J211
		J302	1~15
			J210
		J301
			1~6

AE sensor

Copy Density key

Microprocessor

(Q301)

Copy density correction volume (VR302)

DC controller PCB

Figure 4-204

COPYRIGHT © 1997 CANON INC. CANON NP6218 REV. 0 MAY 1997 PRINTED IN JAPAN (IMPRIME AU JAPON) 4-25