Types of IC Voltage Regulator: Fixed and variable IC voltage regulators
A voltage regulator generates a fixed output voltage of accurate magnitude that remains constant irrespective of the changes to its input voltage or load conditions.
Fixed voltage regulators: 78XX and 79XX
78XX series of IC regulators are three terminal devices that are available with several fixed positive output voltages (e.g. 5v, 12v, 15v etc.). It has three terminals, input, output and ground. The last two digits i.e. XX indicates the output voltage. The variety of output voltages available allow these regulators to be used in logic systems, instrumentation, HiFi, and other solid state electronic equipment. 79XX series is also used to provide the fixed output voltage but in negative. (78XX provides positive output voltage and 79XX provides negative output voltage)
Figure: Fixed Regulator IC 78XX and 79XX Pin out Diagram
78xx and 79xx series ICs do not require additional components to provide a constant, regulated source of power, making them easy to use, as well as economical and efficient uses of space.
These IC’s have built-in protection against a circuit drawing too much current. They are robust and provides protection from overheating and short-circuits.
Fixed Positive Voltage Regulator using IC 78XX:
Figure: Fixed Positive Voltage Regulator using IC 78XX
78XX series of IC regulators are used as positive voltage regulator and have three terminals labeled as input, output and ground. Last two digits that are represented by XX assign the output voltage. In figure standard configuration of a fixed positive voltage IC regulator of 78XX series is given in which C1 and C2 are used.
Fixed negative Voltage Regulator using IC 79XX :
Figure :Fixed negative Voltage Regulator using IC 79XX
79XX series of IC regulators are used as negative voltage regulator and have three terminals labeled as input, output and ground. Last two digits that are represented by XX assign the output voltage. In figure standard configuration of a fixed negative voltage IC regulator of 79XX series is given in which C1 and C2 are used.
Features of fixed regulator IC’s :
1. Programmable output.
2. Facility to boost the voltage/current.
3. Internally provided short circuit current limiting.
4. Thermal Shutdown.
5. Floating operation to facilitate higher voltage output.
6. Versatility and low cost.
7. They are easy to use.
8. Output current in excess of 1A
9. Internal thermal overload protection
10. No external components required
11. Output transistor safe area protection
12. Internal short circuit current limit
Variable and Dual Regulated Power Supply: Regulator IC723
Fixed voltage regulator IC do not have short circuit protection and does not able to provide variable voltage levels. This problem is addressed using variable and dual regulator IC 723. Itcan be used as both positive and negative voltage regulator. It can also be used as a current regulator, temperature controllerand it is available in both dual in line and metal can packages. The range of input voltage is from 9.5 to 40V and can regulate voltage from 2V to 37V.
Figure: IC 723 Regulator IC Pin Diagram
Figure: Internal Diagram of IC 723
Voltage regulators are the devices made to provide constant output voltage irrespective to the changes happening in the input. As we use AC i.e. alternating voltage which is alternating in the nature and there may be chances to sudden increase or decrease in the input which can cause the load devices like laboratory equipments, to malfunction or some time may burnt out. In such cases voltage regulators play important role to protect loads from variation in the input.
Figure shows circuit diagram of IC LM 723 voltage regulator which consists of a voltage reference source, an error amplifier, a series pass transistor and a current limiting transistor. The circuit can provide output voltage in the range of 2 volts to 37 volts with output current up to 150 milli ampere.
The circuit is basically divided into two blocks,
1. Reference voltage generator section
2. Error amplifier section
Zener diode is used is used in reference voltage generator section, which works like voltage regulator and gives constant output. As we have studied, forward bias characteristics of PN junction diode and zener diode are identical but in reverse bias, zener diode will work as voltage regulator. If we use zener diode of say 5v, it provides constant 5v at the output for the input voltage above 5v. You can see practical demonstration of the zener diode as voltage regulator here. Series pass transistor and current limiting resistor is used in error amplifier section. Error amplifier is used to compare the output voltage applied at Inverting input terminal through a feedback to the reference voltage Verve applied at the Non-Inverting input terminal. This connection is not provided internally and so has to be externally provided in accordance with the required output voltage. The conduction of the transistor Q1 is controlled by the error signal. It is this transistor that controls the output voltage.
Features of IC 723 are as follows:
1. Unregulated dc supply
2. Maximum load current.
3. Built in short circuit protection
4. Very low temperature drift.
5. High ripple rejection.
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