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 polarity 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 which can cause an
asymmetry between the half-cycles delivered to the load and thus a
DC voltage component to be delivered to the load; a power supply for supplying power to the controller and provided with power across the
dimmer circuit; 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 duration 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.