Electronic ballast for fluorescent lamps

A frequency-domain analysis is given for a Class D voltage-switching power inverter with a load resistance connected in parallel with a resonant capacitor. Using the fundamental component approximation, design equations are derived to provide easy-to-use design tools. The inverter is inherently short-circuit-proof, but cannot operate safely with an open circuit at the resonant frequency. Safe operation with an open circuit can be achieved if the operating frequency is sufficiently lower or higher than the resonant frequency. Experimental results are given for two F40 fluorescent lamps connected in series, using MTP5N40 MOSFETs. The operating frequency was 50 kHz at full power and 70 kHz at 20% of full power. At full power, the efficiency of the Class D inverter was 95.6% and the efficiency of the power factor corrector was 93%. The overall efficiency of the ballast was 89.4% at full power