In a circuit that turns off a fluorescent lamp, clamping circuitry is provided to dissipate energy stored in a ballast when the lamp is being turned off. In a normal state in which the lamp is on, or in a normal state in which the lamp is off, clamping is not performed as long the VDS of a power switch is below a voltage A. In a lamp turn off operation, the switch is turned on for a time period to extinguish the lamp, and is then made to operate as a clamp (operate in its linear region) for a second period of time to dissipate energy that was stored in the ballast. Clamping in the linear region continues for VDS voltages down to B as ballast energy is dissipated, where B is smaller than A. By clamping down to the lower voltage B, re-ignition of the lamp is prevented.