Values of LM317 regulator that will generate Vout of 5V, 3.3V, 2.5V or 1.2V

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Re: lm317 3.3v

the formula is Vo=1.25*[1+R2/R1]
R1 is selected as 240 ohms 1/4 watt
then for 5V output R2=720 ohms
for 3.3V output R2=393.6 ohms
you cannot get 1.2V output with a LM317 because the reference voltage is 1.25 volts from output terminal to Adj terminal
 

Re: LM317

Look at the datasheet. R1 is 240 ohms for the more expensive LM117 and is 120 ohms for the cheaper LM317. If the resistors are higher value then with some ICs the output voltage will rise when there is no load.
 

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