A ballast circuit is disclosed for inductively providing power to a load.
The ballast circuit includes an oscillator, a driver, a switching
circuit, a resonant tank circuit and a current sensing circuit. The
current sensing circuit provides a current feedback signal to the
oscillator that is representative of the current in the resonant tank
circuit. The current feedback signal drives the frequency of the ballast
circuit causing the ballast circuit to seek resonance. The ballast
circuit preferably includes a current limit circuit that is inductively
coupled to the resonant tank circuit. The current limit circuit disables
the ballast circuit when the current in the ballast circuit exceeds a
predetermined threshold or falls outside a predetermined range.