Low cost self-oscillating ZVS-CV driver for power LEDs

This paper presents a self-oscillating zero-voltage-switching clamped-voltage (ZVS-CV) power electronics driver for LED strings. A simplified mathematical model of LED has been obtained and used to characterize the series resonant converter for the power LED driver. For a large voltage at the input, this converter does not need a current sensor to stabilize the average current through the LED string. By using the proposed converter the effects of the LED manufacturing tolerances and temperature drifts almost has no influence on the LED string average current, and this is analyzed with the application of the LED electrical model. The simplification of the control design, and of the converter, reduces the component number and the cost. The prototype utilizes a low cost series saturable transformer to drive the bipolar transistors (BJTpsilas). The saturable transformer is a component of the self-oscillating drives and determines the switching frequency of the resonant converter. Analytical results are verified by laboratory experiment.