Efficiency improvement of dual mode DC-DC buck converter under light load using PTWS with a zero current detector

This paper presents a dual-mode DC-DC buck converter using power transistor width scaling (PTWS) with a zero current detector to improve power efficiency under light load. The buck converter is operated in a dual mode, combining the switching frequency modulation (SFM) mode which uses the voltage controlled oscillator (VCO) under light load, with the PWM mode for heavy load. To enhance power efficiency under light load a PTWS scheme is employed, in which the inductor current is detected using a zero current detector (ZCD) and then used to select the gate size of the power switching transistor. The proposed circuit was designed using a Magnachip 0.35μm CMOS process. Simulation results shows that our proposed converter has 81.3% ∼ 93% power efficiency for output load currents of 10mA ∼ 250mA, which is a 5.3% improvement compared to a simple SFM-PWM dual mode and an 8.9% improvement compared to a PWM-only mode under a light load of 10mA, respectively.