A RESONANT INVERTER FOR ELECTRONIC BALLAST APPLICATIONS

Electronic ballasts must provide enough open circuit voltage to start the fluorescent lamp and current limiting while the lamp is running. R esonant inverters may be utilized in electronic ballasts because of th eir load-dependent characteristics. The three basic types of resonant inverters, the series-loaded, parallel-loaded, and the series-parallel -loaded, are compared using fundamental approximation techniques for t heir applicability in electronic ballasts operating from a low voltage source. A parallel-loaded resonant inverter operating slightly above its resonant frequency is selected because of the high voltage gains p ossible. Operation above the resonant frequency allows zero-voltage tu rn on of the semiconductor devices. Zero-voltage turn off can be achie ved with the addition of lossless snubber capacitors. Experimental res ults from a lab prototype are used to verify the design procedure.