| 摘要 |
A solid state electronic power switch selectively controls power delivered to a load such as a fan. A momentary contact control switch is provided which is connected to a switching logic circuit whose output state changes when the control switch is activated. A plurality of power control circuits are connected in parallel with one another and in series with a load across a power source. Each of the power control circuits includes either an SCR or a triac element. A turn-on control circuit is provided connected to the SCR or triac for initial turn-on only when a voltage across the element is small compared to a peak-to-peak voltage across it prior to application of gate voltage. With the system of the invention, the load such as a fan can be operated at various discrete power levels without the associated mechanical and electrical noise problems of previous systems.
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