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LM317 Variable Volatage Regulator Electronics Tutorials: 3 Volts To 25 Volts Regulated Power Supply

Updated on February 25, 2012
Image Of a LM317 Ic Used as Variable Volatage Regulator in this Electronics Tutorials
Image Of a LM317 Ic Used as Variable Volatage Regulator in this Electronics Tutorials | Source

LM317 Electronics Tutorials :About LM317

Hi to all And Welcome to another Electronics Tutorials.

Today we are going to talk about the world's most popular variable voltage the LM317 IC, and also how to build it.

LM317 is one of the series of 3-pin adjustable positive voltage regulator. This regulator is capable of supplying excess of about 1.5 amps of current and variable positive output voltage ranging from 2 volts to 37 volts.

Also LM317 are very easy to build and only require two external transistor to complete a basic circuit. Compared to fixed voltage regulators line and load regulation are far more better.

Due to all these advantages it has been used in wide variety of other applications.

LM317 Electronics Tutorials IC Type

LM317 Electronics Tutorials IC Type
LM317 Electronics Tutorials IC Type

LM317 Electronics Tutorials IC Pinout

LM317 Electronics Tutorials Pin Description Of LM317

It consists of mainly 3 pins, one is the adjustable input where it is provided from the potentiometer to adjust the output voltage according to our need

Second pin is the output voltage pin where the variable voltage is available, and it is normally across a capacitor

At last the third pin is the input pin provided from a bridge rectifier or any other constant dc source.

LM317 Electronics Tutorials Circuit Diagram

LM317 Electronics Tutorials:How LM317 Works?

No we take a deeper look inside the circuit diagram and understand how it works:

I have took a bridge rectifier here for the example.

At first the bridge rectifier is connected to ac 230v supply, now the step down transformer steps down the ac voltage to our need say around 25v ac.

Now the ac 25v is converted to pulsating dc of 25 volts using diode bridge rectifier, So the dc is not yet regulated, it's a pulsating and fixed output dc voltage.

So now we need variable dc voltage where we can vary from 2volts to 25volts instead of a fixed voltage, so to accomplish this we use the LM317 IC.

Now to output from the bridge rectifier given to the 3rd pin of the IC. Diodes D1 and D2 are used for the prevention of the ic regulator from over voltages. We use the potentiometer R2 to vary the output voltage according to our needs. At last we can take the output across Resistor C2.

The output from the regulator is a regulated also variable dc supply.

LM317 Electronics Tutorials Youtube Video About LM317 Regulator

Above image shows the formula to calculate the output voltage of the regulator. If any of you are interested to calculate mathematically you can play around resistors R1 and R2 and calculate the output voltages.

I hope you guys understand about LM317 voltage regulator, also please don't forget to rate and comment this hub.

If you guys have any doubt leave a comment on this page, so that i will try my level best to satisfy you with the answer. you can also visit my Electronics Tutorials Blog

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    • profile image


      5 years ago

      Can you please tell me how this formulae is derived?

    • profile image


      6 years ago

      What is 1 ADJ in the formula for calculation of vout?

    • mohanr profile imageAUTHOR


      6 years ago from Bangalore


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