| 摘要 |
PURPOSE:To quickly detect the fact that the motor has gained the prescribed number of revolutions by a method wherein a retrigger type pulse generating circuit, which generates a reference signal, is provided and the pulse widths of the reference signal and the signal of revolution number are compared. CONSTITUTION:The number of revolutions of the motor which drives a disc- shaped recording medium and the like is detected using a detector 6 containing a light-emitting diode D and a photo transistor Q, the result of which is given to a retrigger type monostable multivibrator 10 through the intermediary of a waveform shaping circuit 9, and a reference signal with the pulse width slightly smaller than that of the signal of revolution number is generated. Then, the above is inputted to an NAND gate 12 together with the signal of revolution number, and a high level detection signal is generated by responsing to the fall time using a flip-flop 15. Accordingly, the fact that the motor has attained the prescribed number of revolutions can be detected quickly using a simple constitution, and at the same time, an erroneous detection can also be eliminated, thereby enabling to improve the accuracy of the titled device. |
