Electronic ballast for metal halide lamps based on a class E resonant inverter operating at 1 MHz.

In present paper a new control method and design procedure is introduced for controlling a 1 MHz Class E resonant inverter. Operating in the megahertz range, the appearance of acoustic resonance in a metal halide lamp can be avoided. The high switching losses inherent to the high frequency operation are minimized using a class E resonant inverter. A low cost phase-locked-loop circuit is used for stabilizing the operating point of the inverter. This control circuit modifies the switching frequency within a narrow range to keep a constant phase shift between the lamp voltage and the inverter control signal. The high voltage pulse required to start the lamp is provided by the output resonant filter of the class E inverter without using additional starting circuitry. A laboratory prototype has been built and tested to verify the proposed methodology. The experimental results obtained are also included in the paper.