Figuire 4-109In this condition, the high-voltage transformer sends high voltage that suits the outputof the primary charging level control signal (HVTPC) to the primary charging assembly.If an excess corona current flows from the primary charging assembly because ofchanges in the environment, the return current to the comparator circuit increases,causing the output to decrease. This in turn decreases the corona current from theprimary charging assembly so that the current is controlled to a specific level at all times.In the photo mode, a target value lower than the dark area potential (V D ) target valueused for normal copying mode by about 80 V is used. As such, potential control isexecuted during copying in photo mode for the first time after the power switch is turnedon to control the primary corona current.3. Controlling the Transfer Corona CurrentThe transfer efficiency representing the transfer of toner from the photosensitivedrum to copy paper is affected by changes in the environment (temperature, humidity).To limit changes occurring in the density caused by changes in the environment, thetransfer current is varied according to the temperature and humidity measured by theenvironment sensor.Figure 4-110Humidity (%)Transfer current (+)+--+--DC controller PCBQ156D/AconverterSwitchingcircuitVariablewidth pulseoscillatorcircuitDrivecircuitPrimary high-voltagetransformerTransfer high-voltagetransformerHVTPCHVTTCDCONComparator circuitHVTT501T502 Primary chargingassemblyPhoto-sensitivedrumTransfer chargingassemblyJ202-6J202-5J202-1J114-A5J114-A6J114-A10Variablewidth pulseoscillatorcircuitDrivecircuitMicro-processorCOPYRIGHT © 1997 CANON INC. CANON NP6045 REV. 1 MAR. 1997 PRINTED IN JAPAN (IMPRIME AU JAPON)CHAPTER 4 IMAGE FORMATION SYSTEM4-11
