An Introduction To D.C. Power Supplies

98E m AN INTRODUCTION TO DC. POWER SUPPLIES by Peter Bardos* In this article, Peter Bardos explains the basic workings of power supplies and also considers why they do what they do, and why they behave differently from any other piece of electronic equipment. D.c. power supplies are used in just about every piece of elec- tronic equipment and yet they are taken very much for granted and usually ignored. Never- theless the modern direct-off- line stabilised switch mode power supply (SMPS) is a highly sophisticated and specialist piece of equipment on which the whole equipment will rely for its safety, stability and long term performance. To explain what a direct off-line SMPS is, this article will first discuss what a power supply is. Power Power is defined as the rate of doing work and, in electrical terms, it is given by the voltage multiplied by the current. Energy, which is the related fac- tor, is the capacity to do work and is defined, in electrical terms, as the voltage x t...