Electronic ballast circuit for fluorescent lamps that reduces circuit harmonics

It has been recognized that harmonic currents flowing out from electric and electronic equipment into commercial power lines cause various problems. An international standard (IEC 1000-3-2) was published in 1995 for reducing the harmonic currents. Consequently, domestic requirements are in preparation. The Japanese lighting industry is going to be in self-imposed control from 1997 according to guidelines based on the IEC standard. Some standard circuit techniques have already been established for reducing the harmonics. It is difficult to apply these techniques for electronic ballasts because of the cost of additional circuitry. Thus, simple and low cost methods for reducing harmonic currents are strongly required. We have developed a combined circuit configuration that has a function of harmonics reduction on a half bridge inverter. Self-excited oscillation is achievable by using a current transformer in the positive feedback circuit. Low in-rush current and low harmonic distortion are realized without increasing the total number of electronic parts compared to the conventional electronic ballast. The circuit presented here was applied. to a highly efficient T8 fluorescent lamp lighting system and has been in commercial use.