All-digital current control for capacitor-free multi-channel LED drivers

As system complexity in integrated power electronics increases, modern integrated devices start to substitute analog control by digital signal processing as a result of their superior control characteristics, lower power consumption and less required area. As a recent example, modern multi-channel LED drivers not only act as power supply of LED loads, but also as control unit. This control unit drives single LEDs with discrete spectrum, so that continuous user-defined mixed color is generated. Analog LED voltage and current control for each LED color results in high complexity and a huge component count. To overcome the increased form factor and cost of the state-of-the-art control, all-digital current control at a single supplying inductor is shown. Operating even with zero inductor current during discontinuous conduction mode (DCM), the digital current control offers automatic continuous conduction mode (CCM) / DCM operation. To decrease loop complexity, the single current loop both controls the inductor current, as well as the color mixing in the multi-channel LED driver. The loop has been realized in an FPGA based prototype demonstrator with switching frequencies up to 1MHz and mode changes between CCM and DCM at the slope of 1/L from 5%-95% at a maximum LED current of 200mA.