Linear Regulators

Almost every power supply used in electronics uses a linear regulator as the basic building block. Most linear regulators are so easy to use that they are virtually foolproof. They are usually so inexpensive that they are normally one of the least expensive components in an electronic assembly.

Electronic circuits are designed to operate via a voltage supply. Most of these electronic circuits need the voltage supply to be constant. The voltage regulator outputs this needed constant DC voltage and also possesses circuitry to continuously output the voltage at the needed level. This will be maintained despite changes in load current or input voltage.

The purpose of a linear regulator is to use a controlled voltage current source to maintain the required voltage be available at the regulator output terminal. Control circuitry is required to monitor that output voltage, and vary the current source as required, so that it can produce the output voltage at the necessary value. Designs should limit the voltage source so that the regulator can produce the maximum load current and still maintain regulation.

A feedback loop controls the output voltage. Loop stability is assured by system compensation. Usually, linear regulators allow for compensation by design, and maintain stability without external components. Other regulators may need additional external capacitance supplied by the output lead to ground to maintain regulator stability.

It is very common that a very small amount of time is needed to correct the output voltage by the linear regulator after a change in the demand of the needed load current. The time lag of this response is the label of a phenomena called a transient response. This is a measure of how quickly the linear regulator can prepare for normal, steady operating conditions following a change in load.