Smart electronic switch for low-power loads

Abstract

A two-wire smart load control device, such as an electronic switch, for controlling the power delivered from a power source to an electrical load comprises a relay for conducting a load current through the load, a controller for rendering the relay conductive and non-conductive, and an in-line power supply coupled in series with the relay for generating a supply voltage across a capacitor when the relay is conductive. The power supply controls when the capacitor charges asynchronously with respect to the frequency of the source. The capacitor conducts the load current for at least a portion of a line cycle of the source when the relay is conductive. The controller is operable to determine when the magnitude of the supply voltage reaches a maximum supply voltage threshold, and render the relay non-conductive immediately after the supply voltage reaches the maximum supply voltage threshold.