3.2.7 Main axis control circuit
1. Main axis control circuit is shown as in the following figure 3.2.7.1:
Figure 3.2.7.1 Main axis control circuit diagram
- 87 -
Open disc tray to
proper position
0
0
0
0
0
Open disc tray
0
0.63
0
0
0
0
3.12
0
0
Close disc tray
0
0
0.93
0
0
0
0
3.12
0
2. Function: disc is always in high speed rotation in the course of disc reading, when you need to
open the door to change disc, MT1389 stops the positive direction drive signal which is given to main
axis drive circuit, for the function of inertia disc is still rotating. If disc out order is performed at this time,
disc will be abrasively damaged. Therefore, machine must be baking to main axis, that whether disc has
stopped rotating and whether disc is reversing, decode chip of the machine cannot recognize. So a main
axis control circuit is added to make decode chip can effective monitor that whether disc has stopped
rotating.
3. Working principle: MT1389 has a comparator inside composed of operational amplifier, in which
OP+ is the in-phase input end of operational amplifier, OP- is reverse input end, OPO is output end,
when playing disc normally, for electric machine is positive direction rotating, voltage of OP+ is higher
than that of OP-, voltage of OPO is more than 1.4V. When disc out is needed, main axis drive signal
stops, for electric machine is permanent magnetic, when in rotating, induced electromotive force
produces in two ends to give to decode chip through R204, R205 sampling to make OPO output less
than 1.4V voltage and transmit to input pin of MT1389 ADIN through R207. When ADIN is high level,
main axis drive output end has not any drive signal output, when ADIN is low level, MT1389 outputs a
reversing drive signal to main axis drive circuit to make main axis electric machine speed down. Thus
circular working goes on until main axis stops rotating. PDVD is manual disc out means, so after disc out,
disc is still rotating, but will stop very son.