Introduction: Wiring an Adjustable Voltage Regulator

Picture of Wiring an Adjustable Voltage Regulator

In this simple tutorial I'm going to show how to wire a voltage regulator with a potentiometer to adjust the output voltage. I'm using an LM317T which is readily available and versatile. This Instructable is mostly for the novice, I've tried to cover every detail but is probably overkill for anyone with prior electrical wiring experience.

Step 1: Parts List

Picture of Parts List

 

  • voltage regulator (LM317T shown)
  • schottky diode
  • 240­ Ω resistor (more about the value of this later)
  • 0.1 µF capacitor
  • 10 µF electrolytic capacitor
  • perfboard
  • wire
  • 1 kΩ potentiometer

 

Step 2: Step by Step Wiring

Picture of Step by Step Wiring
  • This is literally step by step, so there is probably a lot of redundancy, I wanted to make instructions that even a complete novice could follow. Each frame is numbered in the left hand corner and will coincide with each numbered step.
  • Step 1. This circuit doesn't take up a lot of space, maybe a square inch or less. placement on your perfboard is something to consider if you plan on wiring anything else to your circuit, and with a voltage regulator you probably will. Also if your voltage demands are high be sure to leave enough room to add a heat sink, these get hot depending on their use. I started in the corner but place it anywhere you'd like.Cut a piece of red wire and strip the ends and insert it into a hole on the perfboard and solder in place.
  • Step 2. Bend the wires of the schottky diode down to resemble a "staple" shape. Diodes are directional, meaning electricity will only flow in one direction through them. This is indicated by the silver band, I think of it a barrel with the band being the open end. Like, you can only fill the barrel from the open end. The band should be placed so the electric supply feed to that end first. Place your diode on the perfboard and solder to the wire already in place.

Step 3:

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  • Step 3. insert the voltage regulator next to the other end of the diode. Voltage regulators are also directional with three pins labeled adjust, out, and in, in that order if your looking at the front of it. The "in" pin should be wired to the diode.
  • Step 4. Next the 0.1 µF capacitor is inserted. This can be inserted in any direction. This is soldered to the "in" pin as well.

 

Step 4:

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  • Step 5. Bend the resistor like what was done with the diode, in the photo I bent mine into a "v" shape to conserve space. Attach one of each end to the two open pins on the regulator, one end to out the other end to the adjust pin.
  • Step 6. insert the electrolytic capacitor. One end will go to the out pin the other will go to ground. This type of capacitor is directional. The side with the white strip on it is negative, this end will go to ground. Solder the other wire to the out or middle pin.

 

Step 5:

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  • Step 8. Cut and strip the end of another piece of red wire, this will connect to the positive wire of the electrolytic capacitor. This wire will be the connection to the positive or supply wire to your device.
  • Step 9. Insert the potentiometer into the perfboard, orient it so that the middle connection is the closest connection to the adjust pin on the regulator. Bend the regulator toward this connection and solder them together.

 

Step 6: Combining Ground Connections

Picture of Combining Ground Connections

 

  • Step 10. Cut a length of solid core wire long enough to join one of the unconnected potentiometer wires to the remaining wires of both the capacitors. connect the remaining potentiometer wire to the one you just soldered the solid wire to.
  • Step 11.Solder the other end of the solid core wire to the ground wires of the two capacitors.
  • Step 12. Cut two more black wires, strip them, and insert them next to the ground wires. Solder these wires to the ground wires as well. One of these will go to supply ground the other will attach to whatever device your trying to regulate voltage for.

 

Step 7:

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  • The red wire in the corner will be from your power supply
  • the other red wire will be to supply power to whatever your supplying voltage to
  • either of the two black wires can go to your device ground
  • the other black wire will go to supply ground
  • the value of the resistor can be changed to suit your purpose as can the value of the potentiometer giving you more higher voltage or to get more precise control of the voltage, or the potentiometer can be changed to a resistor that has a value that will give you the voltage you need, it just wont be adjustable.

Comments

AdeyemoO (author)2017-03-15

What is the functions of the capacitors and how do I wire them

mackiex (author)2015-01-31

Hi can i use 12v 3amp as a supply?

AJackOfAllTrades (author)2015-01-29

Assuming a 9VDC supply, how low can this go? I need a 1.25VDC supply for a specific project I am testing. Also, do you have a schematic you can post? The pictures are great, but will take me a while to decipher. Thanks!

Tom

I can get one I just built to go to less than one volt using a 12v wall wort. If you only need it to be 1.25v you can replace the potentiometer with a fixed value resistor. There is a nice online calculator for this here: http://www.electronics-lab.com/articles/LM317/ , there is this schematic as well as other options.

My intention is that this is a component/building block to a larger project, otherwise I'd had done it on a breadboard.

sbyas (author)2015-01-09

what is the value of the diode? And what is the wattage on the resister?

tbaxter08700 (author)2014-09-29

hi can I connect +12 and -12 from a atx power supply to this? Thanks.

I'm far from being an expert but I'm certain that you can hookup +12 to this and it should work OK. I don't know enough about -12 to really comment on it. It's important that your voltage be within the acceptable range for the voltage regulator your using, with an LM317 transistor that range is 1.2 volts to 37 volts, so 12 volts is fine. if you were to use a voltage source with different outputs you should probably build one of these circuits for each output. I'd probably recommend doing some experimenting with some low risk voltage sources, like a wall wort, in order to determine if the results are acceptable.

This is really helpful, thanks!

Abrar2741 (author)2014-04-17

gr8, easy to follow, easy to make

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Bio: A combination of paradoxes, I love to create useless stuff of novelty. The less functional a project is, the more I'm interested in it ... More »
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