SWITCH-MODE POWER SUPPLY DESIGN

Abstract

In the 1960s, demands of the space programs led to the development of highly reliable, efficient and lightweight electrical power systems for spacecraft. Despite the limited supply of available energy onboard the spacecraft, engineers found innovative solutions for power processing and management of electrical power. These helped usher in the era of modern power electronics. Today, similar limitations on sources of available energy are becoming a prime design consideration in everyday electric power processing. Power electronics is entirely devoted to switchmode power conversion and deals with modern problems in analysis, design, and synthesis of electronic circuits as applied to efficient conversion, control, and regulation of electrical energy. Design and optimization of dc-to-dc converters, which offer the highest power efficiency, small size and weight,and high performance,are also included in power electronics. These dc-to-dc converters with isolation transformers can have multiple outputs of various magnitudes and polarities. The regulated power supply of this type has wide applications, par- ticularly in computer systems, wherein a low voltage high-current power supply with low output ripple and fast transient response are mandatory. In addition, these converters connected in a particular configuration result in switched-mode ас power amplifiers with enough bandwidth and high efficiency. Off-line switchers, dc-to-dc single and multiple output power supplies, bi-directional power supplies (battery chargers and dischargers). dc-to-ac inverters, dc-to-ac uninterruptible power supplies, dc-to-ac motor control, power servo control, robotics, and switching audio amplifiers, etc., are some of the examples of switch-mode power supplies. Switch-mode power supplies have come into widespread use in the last decade. An essential feature of efficient electronic power processing is the use of semiconductors in a power switching mode (to achieve low losses) to control the transfer of energy from source to load through the use of pulse-width modulated or resonant techniques. In ductive and capacitive energy storage elements are used to smooth the flow of energy while keeping losses to a low level. As the frequency of switching increases, the size of the magnetic and capacitive elements decreases in a direct proportion. Because of their superior performance, i.e., high efficiency, small size and weight and relatively low cost, they are displacing conventional linear (dissipative as they operate in linear or conduction mode) power supplies even at very low power levels. The modeling, analysis, and design of these switching dc-to-dc converters have been extensively carried out, and it is commonly believed that the designs in the commercial use today employ the simplest possible converter topology for dc-to-dc conversion. Industry has been quick to realize that the energy saving technique also affords the oppor- tunity to make dramatic reductions in equipment size and weight. Consumer and industry applications are expanding rapidly. Among the various approaches developed for modeling and analysis of the switching dc-to-dc converters, the current-injected equivalent-circuit aр- proach and state space average approach are used in producing a linear-equivalent circuit model that correctly represents the nonlinear converter pro- perties for the static as well as dynamic ac small signal at low frequency levels, the essential features of the input and output transfer properties. Availability of the above model allows choice of the best converter for a specific application and optimization of the feedback loop of a regulator con- taining such a converter.