13
PN301
18
19
16
R317
R318
C332
C335
Q302
C331
C333
CD LD
CD PD
DVD LD
IC301 SSI3723
DVD PD
Q303
R315
R316
Vcc
5V
Vcc
5V
22
27
DVD-
MD
DVD-
VR
DVD-
LD
LD
LD
CD-
PD
CD-VR
CD-
LD
DVD-LD(LASER DIODE)
CD-LD(LASER DIODE)
PICK-UP Unit
Monitor
Diode
Monitor
Diode
22
24
21
23
21
1-2. APC Circuit Operation
It drives the LD to the constant current and adjusts the LD input current , so that the output current is
constant.
IC301 (SSI3723) Pin , : PD IN, Monitor Input of Laser diode APC
IC301 (SSI3723) Pin , : LD OUT, External Current Driver Control output of the LD (Laser Diode)
The detect current from the monitor diode converts to the I/V (Current/Voltage) at the external resistor.
Beforehand, it adjusts a fixed level over for a standard GND.
If this voltage inputs to the PD IN (IC301 Pin 23, 24), it is amplified about 36.4 times (about 31.2dB).
So this voltage outputs from the LD OUT (IC301 Pin 21, 22).
The LD driving element (Q302/Q303) uses the TR more than 200hfe, and controls LD OUT (IC301 Pin 21,
22) connected to the base of Q302/Q303.
The APC control for the each DVD/CD sets Register of the IC301 (SSI3723) according to Disc in the
µ-COM.
DESCRIPTION OF CIRCUIT
1. APC (Automatic Power Control) Circuit
1-1. APC Circuit Constitution
23
24
21
22