Resonant power converter having variable output power or switching frequency

A resonant converter for driving a device, particularly a gas discharge lamp, where the converter is adapted for actively or passively controlling at least one input parameter of a resonant circuit and/or at least one resonant component in a resonant circuit of the converter so as to vary either the output power of the device or the switching frequency, while keeping the other substantially constant, or without substantially influencing the other. The input parameter may be input current or input voltage. The resonant component may be a capacitor and/or and inductor, and the contribution of this component to the impedance of the resonant circuit may be varied. The resonant component may be a MOSFET gate drain parasitic capacitor. A feedback control loop may be provided to regulate either the output power or the switching frequency.