Voltage regulator is an electronic device that supplies a constant voltage to a circuit or load. The output voltage of the voltage regulator is regulated by the internal circuitry regulator to the relatively independent of the current drawn by the load, the supply or line voltage and the ambient temperature.

A voltage Regulator may be par of some larger electronic circuit, but is often a separate unit a module, unusually in the, form of an integrated circuits. It is comprised of three basic parts.

1) A voltage reference circuit that produces a reference voltage that is independent of temperature and the supply voltage.
2) An amplifier to compare the reference voltage with the fraction of the output voltage that is fed back from the voltage regulator output to the inverting input terminal of the amplifier.
3) A series pass transistor of combination of transistors to provide an adequate level of output current to the load being driven.

The combination of the amplifier (often called an error amplifier) and the series pass transistors, together with the resistive voltage divider to tap off a portion of the output Voltage, constitutes a feed back amplifier. The closed loop amplifier configuration acts to maintain the traction of the output voltage feed back to the amplifier inverting input terminal equal to the reference voltage that is supplied to the non-inverting input termines.

Three Terminal Voltage Regulator

Three terminal voltage regulators are voltage regulators which the output voltage is set at some predetermined value. They therefore, do not require any external feed back connections. As a result, only three terminals are required for this type of generator, input (Vin), output (Vo) and a ground terminal. Since these regulators operate at a present output voltage, the current limit resistor Rd is also internal to the generator.

The principal advantage of three terminal regulator is the simplicity of connection to the external circuit, with a minimum of external components required. Indeed, in many applications external components are required. The simplicity and case application is evident. The capacitor across the input terminals is required only when the voltage regulator is located more than about 5 cm.

From the power supply filter capacitor such that the lead inductance between the supply and the regulator may cause stability problems and the regulator may cause stability problems and high frequency oscillations. A very low Effective Resistance (ESR) should characterize the capacitor. Acceptable values on generally 021 geF ceramic disks, 2mF or greater tantalum, or 25mF or greater aluminium electrolyte.
A capacitor is generally not needed across the output terminals. The use of a suitable capacitor will, however, improve the regulator response to transient change in the local conditions, and will also reduce the noise present at the output.

Although, the three terminal regulator offers only output voltages, there are a wide of voltage available both positive and negative. The output voltage available three terminal voltage regulators are 5, 5.2,6,8,10,12,15, 18 and 24V in both positive and negative output voltage. The output current from 100m A to IA.

The three terminal regulators generally offer a line regulation of about 0.005 to 0.02%V, a local regulator of 0.1 to 10% and a ripple rejection of 65 to 85 dB.