LM317 to output 3.3 Volts

I created a simple circuit using the LM317 to output 3.3 volts from a 5V or greater input voltage. Why? Because, a number of modules for the Arduino (or Pinguino) take 3.3 Volts. It’s true, some of the Arduinos do have a 3.3V voltage regulator (and thus a source of 3.3V), however, that might not have sufficient amperage. Also, if  you are a fan of the DIY (Do-It-Yourself)  Pinguinos (as I am), you will need a 3.3V source to accompany them since they do not have one.

So, it is quite handy to have a 3.3V power source around! Here is what the circuit looks like:

LM317 3.3 V Circuit Top ViewLM317 Circuit Side View

I save the foam pads, that came with PC motherboards I bought, and cut out pieces to place under the circuits I make to protect against short circuits. The pads are held in place with two-sided sticky tape.

Here Is the Fritzing circuit diagram:


LM317 3.3V Circuit Diagram

If you’d like the Fritzing source to the above diagram, download it from here.

The LM317 is an adjustable  linear voltage regulator. It can take an input voltage of 3-40 Volts DC and outputs a fixed voltage from 1.2 to 37 Volts DC. The output is controlled by resistors on the adjustment pin. Here is a handy calculator to calculate the resistance needed to obtain the desired output voltage. I use 545 Ohms (470 + 75) to output the desired 3.3V.

Notice that I have a two pin header or a power jack as input source (on the right of the pictures) and the output is a two pin header (on the left in the pictures).

I tested this circuit using the ESP8266 and the NL6621-Y1 modules that I wrote about in earlier articles. These modules require 3.3V and both worked fine.

I thought about integrating this circuit on the DIY Pinguino boards I made and might do that next time I get around to making more of them. However, I think the stand alone circuit is more flexible to use. For example, you can attach a USB to RS-232 cable (like this):

USB to Serial Cabledirectly to the circuit (5V Input and GND) and to the wireless module (Tx and Rcv from the cable, 3.3V and GND from the circuit)  and not even need an Arduino / Pinguino.


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    • DesironnA on November 16, 2017 at 3:06 pm
    • Reply

    Amazing ! I built it and the output voltage is exact 3.3 V. Beautiful and great job.

    • brbrbrbr on June 5, 2018 at 11:28 pm
    • Reply

    Why does this work? The min Vdrop is 3V? I’m also planning to drop 3.7v to 2.4v but I’m not sure if this can be done by LM317

    1. Are you sure of the minimum voltage drop? Take a look at the LM317 technical documentation. Also look at several of the calculators for the LM317(like https://circuitdigest.com/calculators/lm317-resistor-voltage-calculator)

    • Vaughan on November 16, 2018 at 12:59 pm
    • Reply

    What is the purpose of those capacitors?

      • earl on November 19, 2018 at 5:30 am
      • Reply

      The capacitors provide current when the source doesn’t. They would not be needed if the power source was perfect but is that ever the case. You can find more info about this with a search on ‘smoothing capacitors’.

    • fredd on December 11, 2018 at 7:18 am
    • Reply

    I’m going to try build it

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