Low voltage overcurrent protection for solid state switching system

摘要

A current sensing transformer (57) having a low impedance primary winding (100) is connected in series with a filter (38) and load circuit (24) supplied with output current by a high frequency switching PWM power supply (20) such as a sinewave dimmer. Sensed output current is supplied to a microprocessor based programmable controller (56). The controller (56) performs a routine including a family of overcurrent tests (116, 118, 120). Tests of the family are satisfied by the presence of different output current values for different time durations. At least one (120A, 120B) of the tests is enabled only at low requested output voltages or dimming levels. In response to satisfaction of any of the tests, a series power switching stage (26) of the power supply (20) is rendered nonconductive to shut down the power supply.