3. Keeping the Primary/Transfer Corona Current at a Specific LevelIf an excess (or inadequate) corona current flows from the primary chargingassembly or the transfer charging assembly because of changes in the environment, thelevel of the return current to the current control circuit will be higher (lower).In such cases, the current control circuit controls the primary/transfer drive circuit sothat the current on the secondary side of the respective high-voltage transformer will besmaller (larger). At the same time, the return voltage on the secondary side is introducedto the voltage control circuit to control the primary/transfer drive circuit, thereby keepingthe primary side voltage constant.As shown in Figure 4-105, the shielding plate of the primary charging assemblyreceives the corona current generated by the primary corona wire. The high-voltagepower supply PCB (HVT) monitors the level of this current at all times; if it finds it to bedifferent from the standard value (-1.2 kV), the primary/transfer drive circuit starts tocontrol the primary corona current so that the current remains at a specific level at alltimes.Figure 4-105CHAPTER 4 IMAGE FORMATION SYSTEMCOPYRIGHT © 1997 CANON INC. CANON NP6330 REV.0 MAY 1997 PRINTED IN JAPAN (IMPRIME AU JAPON) 4-71200VconstantR123~R125 R104Primary coronawireGridPhotosensitive drumHVTAC Drive circuiteCurrent control circuit
