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.
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 :
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
Step 2: Assemble the Circuit!
As you looked through the datasheet, the simplest circuit we can have to make this guy work, the circuit picture is atacched, We will use :
R1 = 180 ohms resistor
R2 = 10 K ohms potentiometer
Connect the power supply on input and ground, your multimeter in Vout and ground then let's see how it goes!
Step 3: Test It
* Cell phone charger
* ATX supply from your PC or workbench
* Your laptop's power supply
* 9V battery
Any of these should work
Just connect the power source in Vin and your multimeter in Vout, it should look like the presentation video, where I can go from 1.25V to a value nearby Vin - 2V
If you have issues, please comment that I will try to help.