The most common voltage regulator is the three-terminal voltage regulator. The voltage regulator comes in a small package that is shaped like a small rectangular prism. This package often measures no more than one-half inch on a side and is only a little over an eight of an inch wide. It has three long metal leads, a little over an inch, that extend from one side. The voltage regulator package is often made of plastic or steel. Steel versions usually are for applications that require higher electrical current. Plastic versions often come with a metal heat sink attached.
The primary function of a voltage regulator is to provide a constant output voltage. The voltage regulator is provided a voltage level from a battery. The voltage regulator converts the battery voltage level to a different fixed or adjustable voltage level. Unlike a battery, the voltage regulator does not store energy. You can not power a circuit with a voltage regulator alone. The voltage regulator needs a battery so that it can provide power to your circuit.
The two most important voltage regulator specifications include the input voltage and output voltage. The designer selects the input voltage based on the battery voltage that is available. Similarly, the designer selects the output voltage based on the voltage supply requirements of the electronic circuits that need to be powered. For example, an automobile designer will often select a voltage regulator with an input voltage specification of 12 volts, since automobiles use 12-volt battery supplies. As well, an automobile designer will often select a voltage regulator with an output voltage specification of 5 volts, since many electronic devices in the automobile require a 5 volts to operate correctly.
There are numerous types of voltage regulators. These include positive voltage regulators, which are used to convert positive supply voltages to different positive voltage levels. There are also negative voltage regulators, which are used to convert negative voltage levels to different negative voltage levels. Additionally there are fixed and adjustable voltage regulators. Fixed voltage regulators will only produce a specific voltage out for a given input voltage range. Adjustable voltage regulators permit the output voltage of a regulator to be changed. This is often done by connecting a variable resistor to the voltage regulator.
A voltage regulator feature, which is of major concern to electronic designers, is the voltage regulator's ability to provide a constant voltage level out over a wide range of input voltages. This feature is often referred to as the line regulation. An ideal voltage regulator would always provide the same output voltage regardless of the level of the input voltage. However, in real life, a voltage regulator's output voltage will vary slightly with changes in input voltage. For example, a 5-volt voltage regulator might typically produce 5.006 Volts out when the input voltage is 25 volts and 5.000 volts when the input voltage is 7 volts.