| 摘要 |
An interface circuit cooperates with an existing power-stealing circuit designed for use with low voltage AC power. The existing power-stealing circuit provides low voltage DC power for operating an auxiliary circuit and for switching power for an AC load. The existing power-stealing circuit has a semiconductor switch for switching power to the AC load, and a control circuit that when the load receives power, shuts off the semiconductor switch near the zero crossing points in the power voltage waveform and converts the voltage to DC for use by the auxiliary circuit. The interface circuit is interposed between the semiconductor switch and the control circuit of the power-stealing circuit, and reduces the high voltage AC power to the lower voltage for which the power-stealing circuit was designed. In a preferred embodiment, a power field effect transistor drops the voltage applied to the control circuit to a level compatible with the control circuit while the semiconductor switch is open and the load unpowered.
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