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Elements of a Power Supply


When dealing with electronic circuits, we have to meet the basic requirement of providing electrical power for them to work. Without that power, your circuit is no more useful or meaningful than a single raindrop in a hurricane.

The basic purpose of a power supply is to provide one or more fixed voltages to the working circuit, with sufficient current-handling capacity to maintain the operating conditions of the circuit. The power source doesn't have to be fancy; the typical hand-held transistor radio uses a 9-volt battery as its power source. A flashlight uses cells that are physically much larger, but provide a lower voltage. Major electronic appliances such as television sets, VCRs, and microwave ovens have electronic circuits built in that take power from a wall socket and convert it to the form and voltages required by the other internal circuits of the appliance.

Although each power supply has its own individual specifications and characteristics, all power supplies have certain characteristics in common. We'll look at the main parts of a power supply on this page and see how they work together. Then, on subsequent pages, we'll take a more detailed look at each of the parts we haven't seen before, and explore the major variations that are commonly used in modern power supplies.

The Main Sections

A basic power supply consists of three main sections, as shown in the block diagram below and to the right. Depending on the requirements for a given power supply, the sections can be very simple or extremely complex, or even left out altogether in certain circumstances. Each of the sections serves one or more specific purposes, as follows:

General block diagram of a power supply.

Each of the three sections identified above can have a number of variations — even the transformer, which we covered in an earlier page on transformers. Regardless of these variations, each section performs its specific task. However, some circuits do the job more effectively than others, or pick different trade-offs between possible alternatives. To measure the effectiveness of each circuit, we compare the magnitude of the remaining ac component, or ripple, with the dc component of the total voltage appearing at the output of that section. The ratio of ac voltage to dc voltage is known as the ripple factor. The goal of any power supply design is to reduce the ripple factor as much as possible, or at least to the point where the load circuit will not be adversely affected by the remaining ac ripple voltage.

In the remaining pages in this group, we will examine typical circuits and variations used for rectifiers and filters, and compare their performance.

Prev: AC: Filters Next: Basic Rectifier Circuits

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