Patent ID: 8664881

Claim:
A load control device for controlling the amount of power delivered from an AC power source to an electrical load to a desired amount of power, the load control device comprising: a bidirectional semiconductor switch adapted to be coupled in series electrical connection between the AC power source and the electrical load for conducting a load current from the AC power source to the electrical load, the bidirectional semiconductor switch having a control input for rendering the bidirectional semiconductor switch conductive and non-conductive; and a control circuit receiving a signal representative of a voltage developed across the bidirectional semiconductor switch, the control circuit operable to determine a half-cycle start time near the beginning of a half-cycle of the AC power source in response to the signal representative of the voltage developed across the bidirectional semiconductor switch; wherein the control circuit: conducts a control current through the load so as to generate a gate drive signal that is operatively coupled to the control input of the bidirectional semiconductor switch; drives the gate drive signal to a first magnitude to render the bidirectional semiconductor switch conductive after a first variable amount of time has elapsed since the half-cycle start time; maintains the gate drive signal at the first magnitude after the bidirectional semiconductor switch is rendered conductive, such that the bidirectional semiconductor switch remains conductive independent of the magnitude of the load current conducted through the bidirectional semiconductor switch; drives the gate drive signal to a second magnitude to render the bidirectional semiconductor switch non-conductive after a second fixed amount of time has elapsed since the half-cycle start time; controls the second fixed amount of time to be approximately equal during each half-cycle of the AC power source; varies the first variable amount of time in response to the desired amount of power to be delivered to the load to thus control the amount of power delivered to the load to the desired amount.