High efficiency linear regulator

Abstract

A single chip hybrid regulator is disclosed having a first stage being a switching regulator and a second stage being a linear regulator. The switching regulator uses a filter circuit including an inductor and a capacitor. To make the hybrid regulator very small, the inductor value is selected so that the inductor saturates at a current level well below the maximum load current for the regulator. At low load currents, the small inductor does not saturate, and the regulated voltage applied to the input of the linear regulator presents only a small differential voltage across the series transistor of the linear regulator, resulting in very little power being wasted by the series transistor. At higher currents, the small inductor begins to saturate or fully saturates; however, the increased ripple is smoothed by the linear regulator. For applications, such as cell phones, where the regulator operates at low currents for the vast majority of the time, the overall efficiency of the regulator is extremely high and the regulated voltage is very smooth. As the inductor becomes highly saturated, or if the switching regulator cannot supply sufficient current, the switching regulator may be bypassed by the closing of a switch to continuously couple the power supply input voltage to the input of the linear regulator.