Get the LED Out: Experimental Validation of a Capacitor-Free Single-Inductor, Multiple-Output LED Driver Topology

This article presents a new approach for driving multicolor red-green-blue-white ( RGBW) high-current light-emitting diodes (LEDs) for general lighting. The physical advantages in LED applications can be improved by elementary changes in the topology. The presented prototype demonstrator has superior advantages in complexity, form factor, and cost compared to state-of-the-art multicolor LED drivers. A single inductor in parallel to the LED strings is used to supply multiple different LED strings without additional output capacitors. For energy efficiency, the well-known continuous and discontinuous conduction modes (CCM and DCM) are implemented. A novel all-digital current control strategy is used so that no voltage measurements have to be performed, even for light load detection or idle time control in DCM. The irrelevance of any voltage control and the negligence of storage capacitors dramatically reduce the system?s form factor and increase the LED driver reliability. Dimming has been applied with hybrid amplitude and pulsewidth modulation (AM-PWM) control. Thus, color mixing is done by a continuous time integral of the discrete LED light spectra. A discrete prototype demonstrator has been implemented, and further constraints to develop a full integrated circuit (IC) are being evaluated. The discrete demonstrator runs at 12-V dc input voltage with a maximum current of 200 mA to run high-current RGBW LED strings. The peak efficiency of 77.5% is limited by the choice of the applied N-type metal-oxide-semiconductor (NMOS) transistors, which are special and unique on the market for this topology. The high switching frequency of above 1 MHz during CCM ensures a flicker-free color resolution of above 10 b.