Current control and PWM dimming in an automotive LED driver based on a Ćuk converter

This paper presents a current controller for an automotive LED driver based on a zero-voltage switching (ZVS) Ćuk converter using planar integrated magnetics. The driver outputs regulated dc current through a string of N = 1-12 LED's, which implies the need to operate over a wide output voltage range (approximately 3-40 V). It is found that the low-frequency gain of the duty-cycle-to-output-current transfer function exhibits weak dependence on the output voltage, which simplifies the controller design. A simple integral compensator is used to achieve wide-bandwidth control of the output current. PWM dimming is performed by turning the converter on and off, eliminating the need for any additional circuitry or lossy linear current regulators. Converter turn-on and turn-off strategies are introduced to speed up the on/off transients and facilitate high-resolution PWM dimming. Closed-loop current regulation performance and PWM dimming are verified by averaged circuit simulations including a Spice model of the planar integrated magnetics structure extracted by a 3D FEM tool. The controller is implemented digitally and experimental results are presented for a 0.5 A, 3-40 V prototype operating at 2 MHz.