| 摘要 |
PROBLEM TO BE SOLVED: To obtain an overload detection circuit by which an overload is detected with good efficiency without spoiling the driving current of a motor by a method wherein the cycle of an expected-rotational-speed signal is compared with the cycle of an actual-rotational-speed signal, the overload is judged when their difference becomes a prescribed value and a stop signal is output to a motor control circuit so as to stop the motor. SOLUTION: An actual-rotational-speed generation circuit 5 generates an actual- rotational-speed signal on the basis of a frequency signal which is output from a rotational-speed detector 4. In addition, an expected-rotational-speed generation circuit 6 generates an expected-rotational-speed signal on the basis of a PWM signal which is output from a motor control circuit 1. Then, after the end of a starting timer 7, the operation of a rotational-speed comparison circuit 8 is started, the cycle of the expected-rotational-speed signal is compared with the cycle of the actual-rotational- speed signal, and an overload is judged when their difference becomes a prescribed value. By its judgment, a stop signal is output to the motor control circuit 1, and a motor 3 is stopped. Consequently, the overload can be detected with good efficiency without spoiling the driving current of the motor 3. |
