Patent ID: 7190124

Claim:
A dimmer circuit for providing AC power from an AC voltage source to an inductive lighting load disposed in series with the dimmer circuit comprising: a bidirectional semiconductor switch having at least one control electrode provided with a control signal for controlling the amount of power provided to the load, the switch in normal operation being able to be controlled to block voltage in first and second opposite polarity half-cycles of the AC voltage source but in a failure mode being able to block the AC voltage source in only one half-cycle of the AC voltage source and not being able to block the AC voltage source in the second opposite polarity half-cycle; a controller for the switch for determining if said failure mode of the switch occurs; a power supply coupled across said dimmer circuit for supplying power to the controller; the controller controlling the switch if such failure mode occurs so as to: drive the switch into substantially full conduction during most of the half-cycle which the switch is able to control; and drive the switch into non-conduction for a brief interval of time during that same half-cycle so as to prevent a DC voltage component supplied to the load from exceeding a predetermined level below which excessive transformer heating does not occur, thereby minimizing overheating of the inductive load and enabling the power supply for the controller to be provided with sufficient voltage from the AC voltage source to enable the controller to continue to operate.