Description Of Circuit - LG DRD-820B Manual

1. APC (Automatic Power Control) Circuit
1-1. APC Circuit Constitution
DVD-LD(LASER DIODE)
Monitor
Diode
CD-LD(LASER DIODE)
LD
Monitor
Diode
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
IC201 (TA1254F) Pin
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 200h fe , 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.
12

DESCRIPTION OF CIRCUIT

PN201
20
22
LD
10
9
PICK-UP Unit
44 , : MD IN, Monitor Input of Laser diode APC
5
4
45 , : LD OUT, External Current Driver Control output of the LD (Laser Diode)
DVD-
MD
DVD-
LD
R201
R202
R205
CD-
MD
CD-
LD
R217
R218
Q202
R221
Vcc
5V
C201
R203
Q201
D201
Vcc
5V
C216
R222
D202
IC201 TA1254F
44
MDI (DVD)
LDO (DVD)
45
5
MDI (CD)
4 LDO (CD)