A Novel Dimming Electronic Ballast with Improved Crest Factor Using Valley Fill Current Source Resonant Inverter

In this paper, a high power factor dimming valley fill electronic ballast based on a half-bridge current source resonant inverter using continuous variable frequency control is presented. The advantage of using a current fed resonant inverter in the proposed power circuit is that it provides isolation to the driver circuit without the use of any isolation devices. The input inductors of the inverter introduce a new operating mode that is able to shape the input current when the inverter is combined with a valley fill circuit using output current regulation. A simple modified 555 timer is used to continuously regulate the lamp current by changing the switching frequency. As a result, dimming capability and low lamp crest factor are achieved with high power factor to be maintained. A detailed description on the operating principles of the proposed circuit is given in this paper. Feedback loop analysis is also provided to study the stability issues of the designed controller for the proposed ballast circuit. Powersim (PSIM) simulation and experimental results are presented to highlight the merits of the proposed circuit for a 20 W compact fluorescent lamp