Analysis and design of voltage regulator with adaptive FET modulation scheme and improved efficiency

This paper presents a load adaptive voltage regulator that achieves high efficiency extended to light and heavy load regions. The presented method is named as adaptive field effect transistor modulation (AFM) since multiple field effect transistors (FETs) with different characteristics (different sizes) are applied in parallel such that the number of driven FETs and their respective gate driving voltage are adaptive to load current. The capability of adaptive modulation of FETs' parasitic charges and resistances along with adaptive gate driving voltage allows the optimization of equivalent FET characteristics over a wide load range. Moreover, the AFM operation under load dynamic conditions is studied and a scheme is proposed. The AFM operates at a fixed switching frequency for almost the entire load range. Therefore, it has no impact on the operation and the dynamic performance of a conventional buck VR, and it is easy to implement. In this paper, the concept, design and theoretical analysis of the AFM are discussed and verified experimentally. Even though the simulation and experimental works design example given in this paper is for lower power and low voltage converter with discrete components for demonstration purposes, the AFM may have better improvement in higher power and/or higher voltage applications and in integrated voltage regulators.