Canon MF4690 - ImageCLASS B/W Laser Service Manual

Also see for ImageCLASS MF4690: Reference guide Instructions Starter Guide Operation guide Driver guide

Contents

Chapter 55-25.2 Controlling the Laser Activation Timing5.2.1 Laser ON / OFF Control 0016-1834This is the control where the laser driver turns on / off the laser diode (LD) based on the laser control signal sent from the DCNT board.The following is the circuit diagram for laser control.F-5-2The DCNT board sends the video signal (VDO, /VDO) for image formation and the laser control signal (CNT0, CNT1) for switching the laser operation mode tothe logic circuit in the laser driver IC.The laser driver IC performs laser control based on the combination of CNT0 and CNT1 signals.The following chart shows the combination of the laser control signals (CNT0, CNT1).T-5-15.3 Controlling the Intensity of Laser Light5.3.1 Auto Photoelectric Current Control (APC) 0016-1835This is the control to emit the definite level of laser diode.There are initial APC during initial rotation (note 1) and line space APC during printing (note 2), which are performed in the same procedure. The following is itsprocedure.1) When the laser control signal (CNT0, CNT1) turned into LD APC mode, the laser driver emits LD forcedly.2) After being detected with the photodiode (PD), the LD emission level as current is converted to the one as voltage and compared with the reference voltage (thevoltage equivalent to the target laser level).3) The laser driver controls the laser current until it reaches the voltage of LD target level.4) When the laser control signal turns into LD forced OFF mode, LD is forcedly off and the laser driver converts the adjusted laser level to the voltage of the con-denser and keeps it.Note 1. Initial APCAPC during initial rotation. Laser level is adjusted by APC.Note 2. Line space APCAPC during printing. Adjustment of laser level for one line is performed before writing one line.Operation mode CNT0 CNT1 RemarksDischarge mode L L Discharge of C803Print mode H L Use at normal printingLD APC mode L H Use at LD APCLD forced OFF mode H H Use at masking imageJ931-8-9-5-6-3-2/BDICNT1CNT0VDO/VDOIC902CPULaser driver circuit+5VSCNT boardJ902-2-1-5-4-8-7/BDVDO/VDOJ901-6-3-2ComparatorPD LDC803DCNT boardBD sensorPhoto diode) Laser diode)Laser driver ICLogiccircuitDrivecircuitSampleholdcircuit