So yes, I'm brand new to circuitry, and I'm looking to implement a very simple diagram in order to boost a 3.3v output to 12v output.

I've picked up a lm317T from the local electronics shop and I'm currently supplying my breadboard with 3.3v.

What does the practical application of this look like?

LM317T Diagram

I realize this is super simple for most of you, but I'm not totally up on how it works.

  • Is R2 (resistor 2) connected to the ground?
  • How do I figure out which resistors I need?
  • How do I calculate the formula to take a 3.3V input and dump out a 12V output?

$$V_{out} = (1 + \frac{R2}{R1}) + ADJ_{R2}$$

note: R2 is not adjustable in my scenario, but rather it's going to be a fixed resistor in order to give a consistant output


1 Answer 1


Conventional voltage regulators like the LM317 don't do what you're trying to do. They regulate a higher voltage down to a particular (lower) voltage. If you're trying to boost a DC voltage to a higher level you can convert it to AC, run it through a transformer and then rectify it back to DC, or you could use a DC to DC converter known as a "boost converter" or "step up converter" (or "step up regulator"). See: http://en.wikipedia.org/wiki/Boost_converter

Here's one example of such a part:



Also, depending on exactly what you're trying to accomplish, there might be other approaches. For example, if you aren't necessarily trying to convert one voltage TO another voltage, but rather to control a signal at one voltage using a signal at a different voltage, you may only need a transistor, or perhaps an opto-isolator.

  • \$\begingroup\$ oh interesting. What supplies would I need to build my own step up converter? Or is that going to be way too much for what I'm looking to do? \$\endgroup\$ Nov 29, 2011 at 0:43
  • \$\begingroup\$ Post Edit: End of the day, I'm taking 3.3v out of my Netduino, boosting it to 12v and powering an LED Strip. \$\endgroup\$ Nov 29, 2011 at 1:14
  • \$\begingroup\$ Ah, ok, kinda thought it might be something like that. Probably the most straight-forward way to do that is to have an independent power supply (supplying the correct voltage and amperage for the load), switched by a MOSFET transistor. Use the output from the Netduino pin to control the gate of the MOSFET. Trying to drive a significant load directly off of an output pin from a microcontroller isn't really a good idea... the microcontroller can't usually source that much current and you'll damage it if you draw too much current. Look for a "logic level" MOSFET like an IRL540N or similar. \$\endgroup\$
    – mindcrime
    Nov 29, 2011 at 1:23
  • \$\begingroup\$ something along these lines? \$\endgroup\$ Nov 29, 2011 at 1:32
  • 1
    \$\begingroup\$ Yep, there are a lot of parts available, but you don't necessarily have to sort through all of them to make a decision. After you do this a while, you'll A. memorize certain common, broadly applicable parts, and / or B. learn to use the "parametric search" feature on the various vendor websites. For now, do you know how many amps (total) your LED strip draws? If it's less than 36 (which seems very likely), that IRL540N should work. It's rated for 36A at 25 degrees celsius, with a GS voltage of 10V (but it can take a gs voltage of 16 volts, and can go up to 100V on the drain-source path). \$\endgroup\$
    – mindcrime
    Nov 29, 2011 at 2:15

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