| 摘要 |
PURPOSE:To form a proximity sensor oscillation circuit without causing variance or fluctuation of oscillated amplitude by decreasing a rush current flowing at switching of a transistor (TR). CONSTITUTION:A current flows to a resonance circuit via a resistor R6, TRs 5, 6 and a resistor R1 when an object does not approach a detection coil 1, its voltage is subject to impedance conversion by a TR 7 and fed to a TR 4 and fed back positively via a current mirror circuit 3 to start oscillation. In this case, since the base voltage of the TR 4 is clipped by three diodes D1-D3, a signal with a square form limited to a prescribed value at a positive half cycle of the oscillation amplitude is obtained. The emitter voltage of the TR 4 is a voltage lower than the base voltage by one diode forward voltage drop, and the emitter current is a collector current of one TR 9a of a current mirror circuit 9 so as to limit the current.
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