Self-Oscillating Constant-Current Fluorescent Lamp Driver: Theory and Application

Here, a high frequency AC current-sourcing driver that can feed electrical loads with a constant current independent of the load resistance is presented, analyzed and tested experimentally. The power source is a self-oscillating inverter that includes a resonant network and a current comparing and toggling circuit (CCTC) that is used to generate the control signals of the inverter´s power switches. The power driver can be used to ignite and operate one or several serially connected fluorescent lamps, without the need of additional resonant networks and redesign of the power stage, while still maintaining high efficiency and low output crest factor. The CCTC is realized, in the present work, by a multi-winding transformer that is designed to change the polarity of the gate drive of the power switches whenever the input signal drops to the level of the desired output current and hence, will cause the driver to behave as a current source.