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I'm attempting to build a voltage regulator circuit for a DIY stir plate using a CPU fan supplied to an LM317 voltage regulator circuit. I have everything wired up on a board just like the diagram, but using 1kΩ and 10kΩ resistors (which according to this calculator should give the same voltage out). I'm feeding it 12V of DC power from a DC power supplying up to .3A. Measuring the Vout of the circuit without a load attached gives the expected ~12V and drops to ~0V when I dial the potentiometer down. However, once I add the fan, it won't move and the Vout measures a max of 2.1V.

The fan claims it needs 12V and .1A - I'm assuming this means it's ~120Ω. I've also tried swapping it for resistors that I had laying around.

Measured Vout under various loads:

  • Fan: 2.2V
  • 220Ω: 3.6V
  • 1kΩ: 7.3V
  • 100kΩ: 8.6V
  • 1mΩ: 11.3V
  • no load: 11.3V

For diagnosis, I've tried swapping my R1/R2 resistors from 1k/10k to also try 10k/100k, 100k/1m, and 220/1k (no 100 laying around). It's pretty common to see these as different combinations on other stir plate instructions I've read, and the LM317 calculator says they should give the same voltage. All of these combinations gave nearly identical Vout for the variety of loads. The voltages also stay the same with or without the capacitors, which I read were optional.

Can anyone point me towards what's probably wrong, or how to further diagnose it?

EDIT: Solved! I had the LM317 flipped around backwards due to some bad labeling on the bag the component came in. I checked another company's data sheet and flipping it around fixed it.

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  • \$\begingroup\$ You can't see for yourself that you didn't get the HTML omega symbol right!? You have write "Omega" after the ampersand and before the semicolon, just like a zillion reference sources tell you in detail. In any case, there is no excuse for leaving the mess in your post once you saw it didn't work. \$\endgroup\$
    – Olin Lathrop
    Commented Jan 12, 2012 at 13:07
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    \$\begingroup\$ @OlinLathrop - The Ω entity works in Firefox 10 for me, though not in IE7. \$\endgroup\$
    – Justin
    Commented Jan 12, 2012 at 13:34
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    \$\begingroup\$ @Justin: That's probably because the correct name is "Omega", not "ohm". See w3.org/TR/html4/sgml/entities.html \$\endgroup\$
    – Olin Lathrop
    Commented Jan 12, 2012 at 13:41
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    \$\begingroup\$ @OlinLathrop - Fair enough; I'm just saying that your first comment to the OP may be too harsh since it may have worked on his browser. And it looks like it is/will be supported in HTML5: w3.org/TR/html5/named-character-references.html \$\endgroup\$
    – Justin
    Commented Jan 12, 2012 at 13:53

2 Answers 2

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Solved! I had the LM317 flipped around backwards due to some bad labeling on the bag the component came in. I checked another company's data sheet and flipping it around fixed it.

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I have recently worked on the variable voltage supply. Which is working accurately. I have used the following simple and easy circuit which contains:

1- LM317 regulator

2-1000 uF capacitor (can use 25V)

3-Variable resistance 5k or 10k

4-Diodes 1N4001 or 1N4007

5-Bridge Rectifier

6-Transformer (Step Down with 18 volts output)

7-10 uF Capacitors

Circuit Diagram is given below ( simple and easy ):

Circuit Diagram for Variable DC supply

Thanks !

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