TABLE OF CONTENTS Power supplies are used in most electrical equipment. Their applications cut across a wide spectrum of product types, ranging from consumer appliances to industrial utilities, from milliwatts to megawatts, from hand-held tools to satellite communications.
By definition, a power supply is a device which converts the output from an ac power line to a steady dc output or multiple outputs. The ac voltage is first rectified to provide a pulsating dc, and then filtered to produce a smooth voltage. Finally, the voltage is regulated to produce a constant output level despite variations in the ac line voltage or circuit loading. Figure 23.1 illustrates the process of rectification, filtering, and regulation in a dc power supply. The transformer, rectifier, and filtering circuits are discussed in other chapters. In this chapter, we will concentrate on the operation and characteristics of the regulator stage of a dc power supply.
In general, the regulator stage of a dc power supply consists of a feedback circuit, a stable reference voltage, and a control circuit to drive a pass element (a solid-state device such as transistor, MOSFET, etc.). The regulation is done by sensing variations appearing at the output of the dc power supply. A control signal is produced to drive the pass element to cancel any variation. As a result, the output of the dc power supply...
