Patent ID: 7570031

Claim:
A two-wire load control device for controlling the amount of power delivered to a load from an AC power source, the load control device comprising: a semiconductor switch operable to be coupled in series electrical connection between the source and the load, the semiconductor switch having a control input for controlling the semiconductor switch between a non-conductive state and a conductive state; a timing circuit coupled in parallel electrical connection with the semiconductor switch, the timing circuit having an output for providing a timing voltage signal; a trigger circuit operable to control the semiconductor switch and having a trigger voltage developed across the trigger circuit, the trigger voltage increasing in magnitude with respect to time in response to the timing voltage signal, the trigger circuit characterized by a variable voltage threshold having an initial magnitude, the semiconductor switch operable to change between the non-conductive and conductive states in response to a conduction of a control current through the trigger circuit; and a clamp circuit for limiting the magnitude of the trigger voltage to a clamp magnitude greater than the initial magnitude; wherein when the trigger voltage first exceeds the initial magnitude of the variable voltage threshold after the beginning of a half-cycle of the AC power source, the trigger circuit is operable to conduct the control current, to reduce the trigger voltage to a predetermined magnitude less than the initial magnitude, and to increase the variable voltage threshold to a second magnitude greater than the clamp magnitude, whereby, the trigger voltage is prevented from exceeding the second magnitude.