High Power Factor Self-Oscillating Electronic Ballast to Supply Four Fluorescent Lamps

This paper presents an innovative modification in the conventional self-oscillating driver, in order to supply variable loads. This modification consists of adding an auxiliary output filter supplying a small power resistor, which also includes the primary winding of the self-oscillating transformer. The analysis for self-sustained oscillations is performed by extended Nyquist criterion, which defines the design equations for the ballast component values. A design example is presented, using the proposed circuit in a high power factor electronic ballast supplying four independent lamps. A passive circuit named valley charge pump is used to perform the power factor correction. The ballast supplies four lamps independently, without considerable frequency changes, with an efficiency of 93%, and reaching IEC 61000-3-2 requirements for the input current distortion.