US Patent 8686668 Current offset circuits for phase-cut power control

Apparatus for maintaining at least a holding current in a leading-edge phase-cut dimmer during a period of transient voltage variations, the apparatus connectable to the dimmer and connectable to a load connected to draw current from the dimmer. The apparatus may comprise an edge detector connected to receive a voltage from the dimmer and generate a leading-edge signal in response to a leading-edge of a phase-cut waveform, and a current offset circuit connected to receive the leading-edge signal and draw a supplementary offset current in response to the leading-edge signal, wherein the supplementary offset current is sufficient to maintain at least a holding current in the dimmer during the period of transient voltage variations. The current offset circuit may comprise a holding current circuit which also draws supplementary current in response to an instantaneous value of load current.