Lexmark 5021-0XX - Manual (Page 76)

1-50 Service Manual
5021-0XX
Laser drive control circuit
The laser drive control circuit (LDC) consists of a video signal input
circuit, laser drive circuit, laser diode, output sensing circuit, and
output control circuit. See the illustration.
1. When the video signal is received, the laser drive control circuit
switches the laser diode switch on and radiates according to the
video signal.
2. The radiated laser beam senses the photo detector (PD). The
detected signal is returned to the output control circuit.
3. The output control circuit controls the radiated output to a
constant, by comparing the laser output default with the
feedback value transmitted from the output sensing circuit.
4. The laser beam, scanned by the scanner motor, is sensed by
the beam detector (PD), and then outputs the beam detecting
timing (BDT) signal.