Patent ID: 7786766

Claim:
A control system, comprising: a zero crossing detecting circuit for detecting a zero crossing of an AC signal, wherein the zero crossing detecting circuit includes: a transformer having a primary portion and a secondary portion, wherein the primary portion receives the AC signal, wherein the secondary portion comprises a first terminal and a second terminal, and wherein the first terminal is biased at a first DC voltage level; an output switch operatively connected to the second terminal and having an on state and an off state, wherein the output switch selectively activates an output signal of the zero crossing detecting circuit according to an activation voltage level sensed by the output switch and corresponding to the zero crossing of the AC signal, wherein, while in the off state, the output switch is biased at a second DC voltage level, and a voltage difference between the first and second DC voltage levels substantially equals the activation voltage level; and a controller that monitors the output signal of the zero crossing detecting circuit and controls an operation based on the output signal of the zero crossing detecting circuit.