| 摘要 |
PROBLEM TO BE SOLVED: To provide a revolution speed drop detecting circuit which surely detects that the rotation speed of a d.c. motor such as a fan motor drops below a desired revolution speed and issues detection signal. SOLUTION: To a basic control circuit 1 to rotate and drive a motor by applying field coils L1 and L2 with exciting current, a charge/discharge circuit 4, a smoothing circuit 6 and a comparison circuit 7, etc., are connected, the values of resistors R5 , R6 which decide resistance R3 of the charge/discharge circuit 4, time constant of a capacitor C2 and the value of reference power source of the comparison circuit are selectively set, and, when the revolution of motor drops below a desired revolution speed, the comparison circuit compares the smoothing circuit output of the smoothing circuit 6 to the output of the reference power source, and, according to magnitude of it, an output transistor 8 outputs sensor signal for alarming. Thus, drop of revolution speed is detected. |
