| 摘要 |
PROBLEM TO BE SOLVED: To provide a control circuit for fan motor, in which the motor coil conduction transistor can be protected against abnormal temperature rise at the time of motor overload, while reducing noise and vibration. SOLUTION: Combined current of motor coils 1a, 1b is detected by a current detecting resistor 9, and the current of NPN transistors 5a, 5b is controlled such that the combined current has a constant level. On the other hand, rising and falling of the current of moor coils 1a, 1b are delayed by time constant capacitors 17a, 17b so that the waveform of a coil drive current is made smooth for reducing electromagnetic noise. A frequency-voltage converting (F/V) circuit 145 detects the r.p.m. of a fan motor rotary shaft, based on the output from a fan motor drive IC 4. When the difference between the detected r.p.m. and an r.p.m. command voltage 11 exceeds a specified value, the NPN transistors 5a, 5b are turned off and protected against abnormal temperature rise at overload of the motor. |
