Versatile voltage regulator with LM317

 

This guide is intended to aggregate a great tool to your electronics workbench that will save your life many times :

Imagine that you have a single DC power supply that gives you 12v, and you need to supply 3.3v to your circuit, or 5V, or any other voltage between 1.2v and 10v.

Now, you can do it with just 3 components - LM317 IC, 100-400 ohms resistor , and a 10K or 5K potentiometer.

Cost:

LM317 - 0.5 USD
180 ohms resistor - 0.05 USD
10K ohms Potentiometer - 1.5 USD

Total - 2.05 USD

I live in Brazil, and here electronic components are more expensive than other countries like US, so if you live in another country probably your cost will be lower, but still, I'm very happy.

That's right! I will teach you how to assemble this very simple circuit, that makes life way easier for you, that want different voltages on every project, for a very low cost.

You are not limited to 12V as input voltage by the way, is said on the LM317 datasheet that it supports "any output voltage" as long as ( Vin - Vout ) < 40v - I have not tested with high voltages, but I imagine you won't need them eighter.

You can use it on a breadboard or assemble a PCI and mount it on a box, so it will look nice and will be always at your side in the needed moments. The tutorial covers only the circuitry needed and I stopped it on the breadboard.

Let's proceed and see what's needed

Step 1: Looking at the datasheet

This tutorial is very short (as the task itself), but I think that looking at the datasheet of what we are messing with, is a very good idea, so you can know all the power and limitations of your application.

The link for the datasheet is this :

http://www.alldatasheet.com/datasheet-pdf/pdf/8619/NSC/LM317.html

Here are my personnal notes about interesting stuff:

* it won't work on a load that causes a current below 10 mA - watch out.

* It seems very good that it doesn't set a max output voltage, it just specifies that the difference (Vin - Vout) has to be less than 40V.

* You won't go under 1.25V

* Current limitation on the used package - 1.5A

Comments

[kartik negandhi]

* it won't work on a load that causes a current below 10 mA - watch out.
what does this mean???

[samircury]

Means that the IC does it's job as long as the load requires more than 10 mA, otherwise I'm not sure of what could happen, or not, likely it won't turn on.

It's written in the IC datasheet. I just warned =P

[kartik negandhi]

can it b used to charge any device that requires input 7v..???

[samircury]

It could, but you should do the math, Vin-Vout * Current it needs : will tell you how much heating power will be dissipated into the IC. Then you should provide physical means for it to not fry.

Ah, you should look at the IC's max current in the datasheet, but usually is higher than 1A, so you should be fine.

[tim127]

for long term use you might want a heat sync or a fan so it dosent overheat

[kruser495]

you should add a cap to it to steady things out, but really depends on the application.

[Robot Lover]

It could be done easily enough. Simply add a 0.1uf capacitor between the ground and output voltage, but you probably knew that! : )