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Chapter 7: Power Supplies

By Tim Williams
From The Circuit Designer's Companion, Second Edition

The power supply is a vital but often neglected part of any electronic product. It is the interface between the noisy, variable and ill-defined power source from the outside world and the hopefully clear-cut requirements of the internal circuitry. For the purposes of this discussion it is assumed that power is taken from the conventional ac mains supply. Other supply options are possible, for instance a low-voltage dc bus, or the standard aircraft supply of 400Hz 48V. Batteries we shall discuss separately at the end of this chapter.

7.1 General

A conceptual block diagram for the two common types of power supply linear and switch-mode is given in Figure 7.1.


Figure 7.1: Power supply block diagrams

7.1.1 The linear supply

The component blocks of a linear supply are common to all variants, and can be described as follows:

  • input circuit: conditions the input power and protects the unit, typically voltage selector, fuse, on-off switching, filter and transient suppressor

  • transformer: isolates the output circuitry from the ac input, and steps down (or up) the voltage to the required operating level

  • rectifier and reservoir: converts the ac transformer voltage to dc, reduces the ac ripple component of the dc and determines the output hold-up time when the input is interrupted

  • regulation: stabilises the output voltage against input and load fluctuations

  • supervision: protects against over-voltage and over-current on the output and signals the state of the power supply to other circuitry; often...

Copyright Tim Williams 2005 under license agreement with Books24x7
Products & Services
High voltage power supplies use linear technology to provide one or more DC outputs at voltage levels of hundreds or thousands of volts. Search by Specification | Learn more about High Voltage Power Supplies
Power supplies are devices that produce AC or DC power.  This grouping includes current sources, DC power supplies, AC-DC adapters, DC-DC converters, AC power sources, and DC-AC inverters. Search by Specification | Learn more about Power Supplies
AC power sources provide alternating power and typically have adjustable output values for the testing of component response at various voltages, current and frequency levels. Search by Specification | Learn more about AC Power Sources
AC-DC adapters accept AC input voltage directly from a wall outlet, and output DC voltage. Search by Specification | Learn more about AC-DC Adapters
DC power supplies accept an input power and output the desired form of DC power. Common types of DC power supplies include linear power supplies, switching power supplies, DC-DC converters, and silicon controlled rectifier (SCR) type power supplies. Search by Specification | Learn more about DC Power Supplies
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