Harman Kardon HD750, Technical Manual

Page: 14 / 63

APC
The laser diode has large negative temperature characteristic in its optical output when
driven with a constant current on laser diode. Therefore, the output on processing monitor
photo diode, must be a controlled current for getting regular output power, thus the APC
(Auto Power Control) circuit is composed.
Reference Power Supply
A reference power supply for servo is built-in. The current capacity of the reference supply
is about 3 mA.
V
REF1
= 1/2 V
CC1
= 2.5 V
V
REF2
= 1/2 V
CC2
= 1.65 V
where V
CC1
= 5 V and V
CC2
= 3.3 V
19
LD
2
1
V
CC1
PD
170mV
LASER UNIT
C33
R18
Q1
LDON
20
R
V
CC1
R
R/2
V
REF1
22
R
V
CC2
R
R/2
V
REF2
14
HD750