A novel concept of employing current source inverter in valley fill electronic ballasts with dimming capability and low crest factor

A new concept of using current source resonant inverter in passive valley fill dimming electronic ballast with variable frequency control is presented in this paper. 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. When the proposed inverter is cascaded with the valley fill circuit to achieve power factor correction, the input inductors of the current source inverter introduce a new operating mode that is able to shape the input line current to achieve high power factor. A simple modified 555 timer is used in the variable frequency controller to continuously regulate the lamp current by changing the switching frequency of the resonant inverter. As a result, dimming operations 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. Powersim (PSIM) simulation and experimental results are presented to highlight the performance of the proposed circuit for a 20W compact fluorescent lamp.