Fluorescent lamp inverters using charge pump and partial smoothing capacitors

Abstract

A highly efficient RF suppression circuit for fluorescent lamp inverters based on charge pump and partial smoothing capacitors is proposed. The circuit consists of a pumping capacitor, a partial smoothing capacitor and a control switch. The pumping capacitor is of comparatively small capacitance and the control switch operates to ensure that the pumping capacitor charging current is proportional to the AC power supply voltage even across the interval where the AC voltage is near zero. Effective use of current charging reduces the RF harmonic components in the supply current and improves the power factor. The charging voltage of the pumping capacitor (Vcp) and the charging voltage of the partial smoothing capacitor (Vch) together effect inverter driving of the lamp circuit. When the lamp starts, the control switch provides the high voltage, Vcp+Vch. After the lamp has started, Vcp and Vch are switched in alternation. During the period in which the partial smoothing capacitor is charging, the time constants of the choke coil at the rectifier circuit input and the partial smoothing circuit are optimized, while use of the charging voltage of the pump capacitor prevents the sudden appearance of a charging current at the input. Test circuits exhibited a power factor of 97.4% (well above the 85% rating), and the third to eleventh harmonics were at about half of the rated values, demonstrating the feasibility of a high-power-factor low-RF inverter.