A High-Frequency Digitally Controlled LED Driver for Automotive Applications with Fast Dimming Capabilities

This paper presents a high-frequency, digitally controlled High-Brightness LED driver for automotive applications with fast dimming capabilities. The power converter is based on the magnetically coupled Cuk topology and employs a single, off-the-shelf SMT mutual inductor. The proposed digital control technique exploits the inherent stabilizing effect of magnetic coupling, and combines it with a dedicated duty cycle feedforward technique for step-reference response enhancement during dimming operation. No direct sensing of the LED string current is performed, bypassing the disadvantage of the Cuk topology of having an inverted output polarity. Furthermore, the magnetically coupled Cuk topology is a single-switch solution and it provides inherent filtering of the input and output currents without introducing additional magnetic elements, strongly reducing the total required capacitance and maintaining the small form-factor required in the automotive environment. The paper discusses the theoretical and practical development of the proposed controller. Experimental tests on a 40 W, 1 A, 500 kHz prototype indicate a 0 to 1 A current rise time in the tens of microseconds time frame with excellent damping characteristics and regulation accuracy.