| 摘要 |
A start circuit for a single phase AC induction motor employs an impedance in series with the run winding to develop a voltage drop proportional to the current through the run winding, and a pair of LEDs or another light emitting device across this impedance to produce a light output whose intensity varies with the field current, and hence in a generally inverse relation with motor speed. A solid-state AC current switch, which can be a triac or a pair of back-to-back SCRs, is gated by a photosensitive circuit that includes a photosensitive element. A light conduit, which can be a light pipe or light dome, for example, carries the light output from the light emitting element to the photosensitive element. The device of this circuit is highly reliable, has no mechanical contacts, and is relatively insensitive to temperature and voltage fluctuation.
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