Small and Simple Fan Voltage Regulator

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How-To build a fan regulator with parts list and pictures — Christoph Jadanowski aka FrankisGER

Disclaimer: Neither the Author or takes any responsibility for any damage if you attempt what is shown here. This article is for information purposes only.


There´s probably no need to explain what can be done with a fan voltage regulator. Some time ago, I built a LM-317 based voltage regulator (click opens the how-to). The LM-317 is an adjustable linear voltage regulator. My circuit was made from 4 parts (1 resistor, 1 potentiometer, 1 LM-317 and 1 heatsink) and costs about 1 Euro.

The advantages of this circuit are that it is very exact – the voltage stays the same no matter how many fans are connected to it – and in its power – a maximum of 1 ampere if the LM-317 is well cooled.

The biggest disadvantage of this circuit is that the voltage drop caused by the LM-317 is 1.25 volts. This means that the connected fans won´t get more than 10.75 volts if the regulator´s input voltage is 12 volts.

Today, I wan´t to show you a simpler circuit. The advantages are as follows:

  • The circuit consists from just 2 parts (1 BC337-40,
    1 potentiometer);

  • Cost: About 25 cents;
  • Max. 500mA (enough for für 5 80mm fans);
  • Needs no heatsink;
  • Very easy to build;
  • The adjustment is very exact and stepless;
  • Provides the fans with a maximum voltage of 11.4 volts.

Parts needed

  • 1 100k ohm potentiometer (size and type doesn´t
    matter), cost: about 10 cents;

  • 1 npn transistor BC337-40 (you can use any other npn transistor as long as it provides 500mA or more maximum collector current. When using a stronger one, you can use even more fans), Cost: about 15 Cents;
  • Small piece of PCB (I used a 3 cm * 1cm piece);
  • Some cables (depends on how much you need).

    You should be able to get all of these parts at your local electronics shop or in every online electronics shop.

Circuit Plan + Pictures + Tips



It´s really very simple to build. Connect one fan or more (up to 5; with a stronger transistor, even more) and adjust the voltage with the potentiometer. Be careful not to short-circuit the transistor by shorting the fan connectors (this way, the transistor will burn up or overheat). You can prevent this by adding a pre-resistor (to set the max. current) or by adding a fuse, but I didn´t want to go that far with this article.

Also be careful on where you mount this circuit, because the underside carries 12 volts and ground – you´d best glue it onto some piece of plastic. I built the circuit this way (ghetto!):


It´s one of the smallest fan voltage regulators, i´ve ever
seen. For me, it was a way to get rid of some parts I had lying around
and I hope this circuit can help you. If you are interested in a similar,
but temperature-regulated version, look at this page: The German version of this article can be found here:

Christoph Jadanowski aka FrankisGER


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