State Feedback based Multi-Mode Control Design in Buck LED Drivers with Enhanced Performance and Smooth Transition for Automotive Applications

Small-signal-based current mode control (CMC) and voltage mode control (VMC) design approaches are principally dominant in the existing commercial products on buck converter-based LED drivers for automotive applications. However, the control bandwidth (BW) in VMC is limited for a larger duty ratio variation, while in CMC, the over-compensating ramp may degrade the control BW, penalizing the transient performance. Load-insensitive PID controller tuning in VMC provides enhanced load transient performance, however, beyond the control BW, model validity remains a concern due to low-valued output capacitance. This paper presents small-signal-based state feedback (SF) design approach to achieve nearoptimal recovery during load transients without any load feedforward, even for a higher BW. Thereafter, SF-based multi-mode control strategy with smooth controller transition is identified to provide inherent current-loop stability along with superior light-load efficiency. Simulation results are presented to show the performance improvement using the proposed design approach.