Panasonic KX-MB1520FX7 Service Manual page 39

4. Timing chart of current control
Following timing charts are the example of Vref voltage corresponding to PWM pulse duty.
6.7.2.3. O.C.P (Over Current Protection) circuit
1. Function
If motor driver can supply more than 15 watts, FB motor may become fire hazards.
To prevent the risk of fire, this circuit is provided.
2. Circuit Diagram
3. Circuit explanation
When the current supplied from 24V exceeds 0.44A, the voltage between two registers R575 and R578 becomes more than
0.6V (=0.44A*2.7ohm/2), consequently both Q515 and Q522 turn on.
If Q522 turns on, IC502_pin20 becomes "Low" level.
As a result IC502 is deactivated and motor currents are cut off.
So the current which IC502 can supply is limited to less than 0.44A and the wattage is also limited to less than 10.7W
(=0.44A*24V).
By limiting the wattage less than 15W, risk of fire hazard is eliminated.
KX-MB1520FX7/KX-MB1520FX8/KX-MB1520FXW/KX-MB1530FX7/KX-MB1530FXW
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