Lighting: February 2010 Archives

Well, my favorite discrete component of the week has to be the lowly LM317 voltage/current regulator. As one of my previous posts showed, I'm using it to current regulate some high power LEDs and I also use it as a voltage regulator.

Here's the quick and easy way to wire up an LM317 as a voltage regulator:


where the values of R2 and R1 are calculated as follows to give Vout:


R2 is usually set to 240 ohms and you can ignore Iadj to a point. Rearranging the equation gives you:

R2 = 192 * V - 240

So if you want a 5 volt output, then R2 = 720 ohm (and R1 = 240 ohm). The TO-220 form factor of the LM317 that I'm using can provide up to 1.5 amps of output current and can be paralleled if I need more.

Late update: or you can just use an online calculator:

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This page is a archive of entries in the Lighting category from February 2010.

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