Design of power supplies for fast load transients

Abstract

This thesis aims to provide effective methodologies for designing power supplies with fast dynamic response. A strategy for low-cost and high-efficiency design is to employ an auxiliary circuit which only operates for feeding fast load transients. The design and practical applications of some auxiliary circuits are discussed, along with a proposed classification of auxiliary circuits that provides guidelines for choosing the appropriate type of auxiliary circuits for a given application. The main contributions of this thesis are summarized as follows: Firstly, a general classification of auxiliary circuits is discussed on the basis of circuit configuration, control and load information. Based on the classification, design and application principles of auxiliary circuits are given for various practical scenarios and requirements. Secondly, a low loss bi-directional buck-boost circuit is proposed to work as an auxiliary circuit which is connected at the output port of the main converter. As no extra power source is required, the circuit employs a reservoir capacitor to draw or release energy, aiming to eliminate output voltage fluctuations during load transients. The capacitor may have a non-zero net input power and its voltage may become uncontrolled after many cycles of charging and discharging. A method to regulate the energy storage level within a specific range is proposed. The prototype is constructed to validate the proposed design. Thirdly, a scheme to realize an auxiliary circuit that can cope with the trend of load-informed power management is proposed. The unconstrained sensor band-width and the simplification of the control algorithm are the advantages of this method. The effectiveness of this method depends on the precision of transient predictions. A strategy for tackling inaccurate predictions is also proposed. Two specific implementations are given, along with experimental verification.