C. Controlling the Development Bias1. OutlineFigure 4-204 shows the circuit used to control the development bias; the circuit hasthe 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 level2. Turning On and Off the DC Component of the Developing Bias and Controllingthe Voltage to a Constant LevelThe microprocessor (Q512) on the composite power supply PCB generates theBPWM signal (pulse signal) under the control of the microprocessor master (Q301) onthe 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, theapplication voltage is taken in from the development DC bias voltage detection circuit inthe form of the BIASS signal (analog signal) to exert control so that the output voltage ismaintained at a constant level.The main transformer (T101) is driven by the drive signal (MPWM) from themicroprocessor (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 otherloads.Figure 4-204COPYRIGHT © 1997 CANON INC. CANON NP6218 REV. 0 MAY 1997 PRINTED IN JAPAN (IMPRIME AU JAPON)CHAPTER 4 IMAGE FORMATION SYSTEM4-25Composite power supply PCBMain transformerT101Transformer (T101)drive circuitDevelopmentDC bias drivecircuitDevelopmentDC bias voltagedetection circuitDevelopment AC biastransformerT301BPWMBIASSMPWMJ2111~15J2101~6J302J301DevelopmentAC transformerdrive circuitMicroprocessor(Q512)PhotosensitivedrumDeveloping cylinderAE sensorCopy Density keyDC controller PCBMicroprocessor(Q301) Copy densitycorrection volume(VR302)ACBIAS
