A power supply for a gas discharge lamp is claimed. An input circuit receives power from a power source. An output transformer having a primary winding and a secondary winding and has a lamp connected in circuit across the secondary winding. First and second power switches switch power to the primary winding. The driver drives the power switches at a drive frequency. A tuned LC resonant circuit having a resonant frequency is connected in circuit between the driver and the lamp. A controller generates control signals to the driver at a first frequency that is functionally related to the drive frequency, and regulates the lamp current by controlling the difference between the resonant frequency and the first frequency.
