IC LM 723 voltage regulator

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 equipment, 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: IC LM 723 voltage regulator

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.