| 摘要 |
PURPOSE:To detect a voltage induced across the coil of a motor by an external magnetic field easily and definitely by alternately connecting a high resistance and low resistance to the coil for longer than 20msec and also by ending the detection right before a driving pulse driving the motor. CONSTITUTION:A voltage induced across the coil of motor 20 by an external magnetic field is shorted by the closed loop of N gates 23 and 24. The voltage across the coil is shorted by the lower ON gate of N gate 4, so that a relatively-large current will flow. Next, the switching of the closed loop of motor 20, N gates 26 and 23, and detection resistance 29 develops a momentarily-large voltage across detection resistance 29 since the coil of motor 20 has an inductance component and the voltage is stabilized afterward to a steady value determined by detection resistance 29 and the induced voltage. In this case, the detection time for alternate connections is set to a period of longer than 20msec which is longer than a cycle of 20 or 16.7msec of the general commercial alternating-current frequency of 50 or 60Hz, and the detection should end right before a driving pulse driving the motor. |
