Discrete-Time Trajectory based Control of DC-DC Converters and Applications to LED Driving

High brightness LED application uses a PWM dimming for controlling the luminous output in which the LED driver is subjected to deliver either No-Load or full load current and the brightness is controlled by the duty-ratio of the dimming PWM. In order to avoid flickering, the dimming frequency ranges up-to tens of kilohertz in automotive applications. However, the controller designed based on a small-signal averaged model cannot satisfactorily perform under such dynamically varying load conditions and also results in reduced efficiency because of high switchings during each transients. This paper presents a geometric switching surface based controller tuning to achieve fast transient recovery without the requirement of linearized model. The digital hysteretic modulator guides the converter trajectory during the transient and steady-state. The event-based sampling approach achieves stable periodic behaviour and steady-state frequency regulation is achieved by adaptively varying the hysteretic band in real-time using time-to-digital (TDC) converter. The synchronous buck converter and high brightness LED array prototypes are made and the proposed control scheme is realized using a FPGA device. The time optimal recovery using both resistive load and LED array are demonstrated using the test results.