| 摘要 |
PURPOSE:To make it possible to analoguely detect the number of rotations of a rotor from the charge voltage of a condenser proportional to the number of rotations of said rotor, by providing a rotation detection part, a charge and discharge part, a condenser charging part, a discharge part and a detection part. CONSTITUTION:When the light of a light emitting diode 21 is blocked by a disc and a phototransistor 22 is turned OFF, a condenser 25 is charged. At this time, a continuity state is obtained because the base current of a transistor 26 is flowed and the transistor 26 is not related to the OFF-time of the transistor 22. When the light of the diode 21 reaches the transistor 26 through the slit of the disc, a continuity state is established and the charge of the condenser 25 is discharged as the collector current of the transistor 22. At this time, the base potential of a transistor 30 comes to constant one and, because the voltage between the base and emitter of the transistor 30 is constant one, the emitter potential of the transistor 30, when the transistor 26 is a continuity state, is constant one. Therefore, when a resistor 33 is a fixed one, the collector current of the transistor 30 comes to a constant current. |
