COPYRIGHT © 1999 CANON INC. CANON 660/2100 REV.0 FEB. 1999 PRINTED IN JAPAN (IMPRIME AU JAPON)C. Controlling the Laser IntensityThe auto intensity control mechanism (APC) of the laser diode is controlled by thelaser drive IC (IC1002) to ensure that the laser diode emits light at a specific intensity.The DC controller PCB causes the APC sampling timing signal (SAMPLE*) to go ‘0’for each line of image data. The image enable signal (LENB*) and the laser drive signal(DATA*) go ‘0’, and the laser drive IC (IC1002) enters sampling mode (Note 1). As aresult, the laser diode (LD) turns on, and its intensity is detected by the photodiode (PD).The intensity detected by the photodiode is fed back to the comparator through thecurrent/voltage conversion circuit, and is compared against the reference voltage select-ed in the laser drive circuit IC to control the laser current sent to the laser diode.At the end of a specific period of time (end of unblanking), the SAMPLE* signal goes‘1’, and the printer unit enters hold/print mode (Note 2) to end forcing the laser diode (LD)to emit light. In response, the laser drive IC converts the controlled laser light into a volt-age for retention in a capacitor (C1004).The voltage retained by the capacitor (C1004) is cleared when the capacitor is dis-charged in response to the image enable signal (LENB*) going ‘1’ at the end of each sin-gle line. (Note 3)When video signals are received, the ELENB* signal goes ‘0’, SAMPLE* signal goes‘1’, and DATA* signals are generated; the printer unit enters hold/print mode.Table 3-201 shows the above relationship:Table 3-201CHAPTER 3 LASER EXPOSURE SYSTEM3-6LaserOnOn/OffOffLENB*LLHDATA*LH/L—SAMPLE*LH—APC sampling modeHold/print modeClear modeDownload free service manual at http://printer1.blogspot.com
