Brother HL-2400C Service Manual page 87

(2) Laser Drive Control Circuit
Laser Drive Control Circuit (LDC) consists of the video signal input circuit, laser
drive circuit, laser diode, output sensing circuit and output control circuit, as shown
in Fig.4-34.
<Operation>
(1) When the video signal is received, the laser drive control circuit switches the
laser diode according to the video signal data.
(2) The radiated laser beam is sensed by the photo detector (PD) and the signal is
fed back to the output control circuit.
(3) The output control circuit controls the laser output to make the level constant by
comparing the laser output with the feed-back value transmitted from the output
sensing circuit.
(4) The scanning laser beam is sensed by the beam detector (PD), then the beam
detecting timing (BDT) signal is output.
IV-38