DC Voltage Regulators LM78XX

Here we will study about voltage regulator and how to connect it in the circuit.

What is voltage regulator?

Voltage regulator maintains the desired constant voltage level.  The desired constant dc level may be positive or negative. Depending on the requirement, we use positive dc voltage regulator or negative dc voltage regulator.

Sr no. Requirement IC Packet
1 Positive Supply LM78XX
2 Negative Supply LM79XX

How to connect it to the circuit?

For example, A 5V supply is needed for the circuit, we will use LM7805 IC to get the desired voltage. In LM7805 there are 3 pins,

Pin No. Pin Name Description
1 Input Input Supply from various voltage sources. Input voltage ranges from 7v to 12V.
2 Ground It is connected to the ground of the circuit.
3 Output The desired constant 5V output is obtained from this pin.


Circuit diagram:

Components required:

  1. LM7805 voltage regulator.
  2. Power supply.
  3. 33uf capacitor
  4. 1uf capacitor




Input supply is given to the input pin of the LM7805 from either power supply or battery. It ranges from 7V to 12V. For proper regulation, the input to the IC should be pure dc. This is obtained by using a 0.33uF capacitor at the input side. The power supply provides the dc voltage along with the noise flickers. The input capacitor filters out this noise flickers. Capacitor has the property to block the dc component and allow the ac component to pass through it. The AC component passes through the capacitor and gets grounded and the pure dc component is fed to the input pin of the LM7805.

Similar concept is followed by the output capacitor. LM7805 produces the desired 5V along with the noise fluctuation. The noise voltage produced by the regulator IC is filtered out by using 0.1uF capacitor at the output side.

The pure 5V is obtained at the output of the circuit which is then used for the various circuit which requires 5V.


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