An improved "charge pump" electronic ballast with low THD and low crest factor

The "charge pump" electronic ballast circuit, which employs a charging capacitor and a high frequency AC source to implement power factor correction (PFC), has become an attractive topology for ballasting fluorescent lamps because it eliminates the use of a bulky boost inductor. However, this circuit has the problems of high total harmonic distortion (THD) of the input current, and high crest factor (CF) of the lamp current. This paper analyzes the origin of the problems and proposes a novel solution. With the addition of two small clamping diodes, very good input current (PF>0.99, THD <5%) and lamp current (CF<1.6) can be obtained with open loop control. Experimental results are provided for verification.