Patent ID: 6175220
Filing Date: 2001-01-16
Classification: H05B,Y02B

Abstract:
A system for controlling AC power delivery to a load, said AC power defining an AC voltage, said AC voltage defining a series of AC voltage cycles, each of said AC voltage cycles having zero crossings, said system comprising:an activation input for receiving an activation signal;a switch for selectively coupling a load to AC power, said switch having a switch-control input, said switch in normal condition coupling said load to AC power in response to a coupling command received at said switch-control input;threshold circuitry for detecting when a current-parameter value of a current parameter associated with a current through said load exceeds a threshold value, said threshold circuitry including a sensor for sensing said current parameter;phase tracking means for determining the phase of said AC voltage; anda controller for controlling said switch by sending said coupling command to said switch-control input, said controller in response to receiving said activation signal leaving said load uncoupled from AC power during the first half of a voltage half cycle and then sending at least a first coupling command to said switch at a short-circuit-test phase angle within the second half of said half cycle, said controller being coupled to said phase tracking means, said controller determining whether or not a short-circuit criterion is met, said short-circuit criteria requiring that said current-parameter value exceed said threshold value during at least one short-circuit-test AC voltage cycle, said controller withholding coupling commands during succeeding voltage cycles if said short-circuit criterion is met.