3.2.3 Laser power control circuit
Laser power control circuit is shown as in the following figure 3.2.3.1:
Q301
2SB1132-S
Q302
2SB1132-S
R301 4.7R
R302
4.7R
TC302
47uF/16V
TC303
47uF/16V
LDO-AV33
LDO-AV33
LDO2
LDO1
MT1389E
MD1
20/21
XS301
23
20
19
2. Working principle
Pin 20/21 of MT1389 is laser power detect signal input pin, pin 21 is DVD laser power strong/weak
detect signal input pin, pin 23 is VCD laser power drive control output pin, pin 22 is DVD laser power
drive control output pin.
When reading VCD disc, laser power becomes weak, voltage of MDII pin decreases, voltage
decrease of pin 23 of MT1389 makes voltage of pin 19 of XS301 increase to reach the purpose of raising
laser power. When laser power is too strong, voltage of MDII pin increases to lead to voltage of pin 23 of
MT1389 increase to make voltage of pin 19 of XS301 decrease to reach the purpose of reducing laser
power to form an auto power control circuit.
When reading DVD disc, pin 21 is detect signal input pin, pin 22 is drive control input pin, and the
working principle is the same with that when playing VCD disc.
3. Key point voltage (unit: V) is shown as the following table:
Figure 3.2.3.1 Laser power control circuit diagram
Location number
Read DVD disc
Read VCD disc
Location number
Read DVD disc
Read VCD disc
V103_E
2.9V
3.2V
V104_B
3.2V
2.2V
V103_B
2.2V
3.2V
V104_E
3.2V
2.9V
V103_C
2.2V
0
MT1389_20
0.2V
0.2V
V104_C
0
2.2V
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