Electronic ballast for high-pressure mercury lamps

A ferromagnetic ballast is generally needed to stabilise a discharge lamp, this ballast is expected to be of small size and with low losses. At the moment the use of resonant converters in the electric energy conversion is rapidly expanding. The soft commutation of the switches limits the commutation losses in the semiconductors and therefore enables high frequency operation, thus the dimensions of the magnetic components (transformer, inductors) are noticeably reduced. For these reasons, a new type of resonant converter, which can provide high power in a selected frequency range is developed. Our ballast equipment is composed of an inverter circuit, having variable switching frequency, a series resonant circuit and a starting capacitor. Switches operate in the frequency range 50 kHz-70 kHz. This device is used in order to supply a 1.3 kW high-pressure mercury discharge lamp. The lamp turns on at 70 kHz and operate in nominal operation mode at 50 kHz