12
PN201
20
22
R201
R202
C201
R203
Q201
D201
C216
LDO (CD)
MDI (CD)
LDO (DVD)
IC201 TA1254F
MDI (DVD)
Q202
R221
D202
R222
R217
R218
R205
Vcc
5V
Vcc
5V
10
9
DVD-
MD
DVD-
LD
LD
LD
CD-
MD
CD-
LD
DVD-LD(LASER DIODE)
CD-LD(LASER DIODE)
PICK-UP Unit
Monitor
Diode
Monitor
Diode
4
5
45
44
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.
IC201 (TA1254F) Pin , : MD IN, Monitor Input of Laser diode APC
IC201 (TA1254F) 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 MD IN (IC201 Pin 44, 5), it is amplified about 270 times (about 48.7dB).
So this voltage outputs from the LD OUT (IC201 Pin 45, 4).
The LD driving element (Q201/Q202) uses the TR more than 200hfe, and controls LD OUT (IC201 Pin 45,
4) connected to the base of Q201/Q202.
The APC control for the each DVD/CD sets Registor of the IC201 (TA1254F) according to Disc in the
µ
-COM.
DESCRIPTION OF CIRCUIT
1. APC (Automatic Power Control) Circuit
1-1. APC Circuit Constitution
44
5
45
4