New design of high performance electronic ballast and the control IC implementation

Abstract

In this dissertaation, several circuits are presented to improve the performance of typical self-exciting half-bridge series resonant electronic ballast for fluorescent lamps. These circuits include a fast swithing gate driver, an improved valley boost full power factor correction circuit, and so on. Moreover, to achieve high reliability as well as small size and low cost, the control IC for the electronic ballast is designed after the control circuits have been developed and implemented by using discrete components. A fast switching gate driver is presented. This shortens the turn-on/off transient of MOSFET switches by amplifying small gate drive current with the aid of positive feedback strcture. The gate transition time becomes extremely fast about 20nsec. Also, the full saturated transistors hold the two MOSDETs simultaneously in the off state, resulting in dead interval. Thus, additional capacitors can be connected in parallel with the MOSFETs. This has negligible switching loss by zero voltage switching, and reduces in harmonic noise because the switching voltage has a nearly trapezoidal, rather than square, waveform. Note also that gate driving loss is considerably reduced by small driving current. Experiments show that the power loss of this gate driver is as small as one fourth of that of conventional gate driver. In addition, the proposed gate driver has a very high frequency driving capability over 150kHz during the initial start up period before the lamp is lit. A new power factor (PF) correction topology called improved valley fill (IVF) is also presented. This has different charging a action to the electrolytic capacitors, and can adjust the valley voltage higher than half the peak line voltage. Consequently, there is no pulsating line current around the line peak, and the PF and THD are significantly improved. The IVF also improves lamp current crest facotr (CF) by soft power transfer operation. To obtain unity power factor, in addition, a valley...