Purpose of Voltage Regulator:
Voltage regulators are used in power supplies to regulate or eliminate variations from DC voltage. This stage is the important part of Power Supplies, it regulates the DC voltages required at the output of power supply. If these regulators don’t work properly, our sensitive electronics equipments may blown off.
Integrated Circuit Voltage Regulators:
While filters can reduce the ripple from power supplies to a low value, the most effective approach is a combination of a capacitor input filter used with a voltage regulator. A voltage regulator is connected to the output of a filtered rectifier and maintains a temperature. The capacitor input filter reduces the input ripple to the regulator to an acceptable level. The combination of a large capacitor and a voltage regulator helps produce an excellent power supply.
Most regulators are integrated circuits and have three terminals, an input terminal, an output terminal , and a reference (or adjust ) terminal. The input to the regulator is first filtered with a capacitor to reduce the ripple to < 10%, the regulator reduces the ripple to a negligible amount, in addition, most regulators have an internal voltage reference, short circuit protection, and thermal shutdown circuitry. The are available in a variety of voltages, including positive and negative outputs, and can be designed for variable outputs with a minimum of external components. Typically, voltage regulators can furnish a constant output of one or more amps of current with high ripple rejection.
Three terminal regulator designed for fixed output voltages require only external capacitors to complete the regulation portion of the power supply, as shown in below diagram. Filtering is accomplished by a large value capacitor between the input voltage and ground . An output capacitor (typically 0.1 µF ) is connected from the output to ground to improve the transient response.
A basic fixed power supply with a +5 V voltage regulator is shown in below diagram. several types of both linear and switching regulator are available in intergrated circuit (IC) form. Generally, the linera regulating are three terminal devices hat provide either positive or negative output voltage that can be either fixed or adjustable, In this section, typical linear and switching IC regulators are introduced.
Fixed Positive Linear Voltage Regulators:
Although many types of IC regulators are available, the 78XX series of IC regulators is representative of three terminal devices that provide a fixed positive output voltage configuration . The three terminals are input, output and ground as shown in the standard fixed voltage configuration. The last two digits in the part number designate the output voltage. For example, the 7805 is a +5.0 V regulator, Other available output voltages are given in Diagram and common packages are shown.
Capacitors, although are not always necessay, are sometimes used on the input and output as indicated in this diagram, The output capacitor acts basically as a line filter to improve transient response. The input capacitor is used to prevent unwanted oscillations when the regulator is some distance from the power supply filter such that the line has a significant inductance.
The 78XX series can produce output currents up to in excess of 1 A when used with an adequate heat sink. The input voltage must be at least 2 V above the output voltage in order to maintain regulation. The circuits have internal thermal overload protection and short circuit current limiting features. Thermal overload occurs when the internal power dissipation becomes excessive and the temperature of the device exceeds a certain value. Almost all applications of regulators require that the device be secured to a heat sink to prevent thermal overload.
Fixed Negative Linear Voltage Regulators:
The 79XX series is typical of three terminal IC regulators that provide a fixed negative output voltage. This series is the negative voltage counterpart of the 78XX series and shares most of the same features and characteristics. Below diagram is standard configuration and part number with corresponding output voltages that are available.