Electronics 2000 Forum

[sparkfishes]

I know the formula for calculation R1 and R2 when using the LM317T voltage controller however, I am never quite sure how one obtains the value for the amps value for amps on R2 adjust
What value Voltage does one use for the current through R2 ( adjust) assuming V/R = A?


I usually find just using the other parameters gives be a close enough result 1.25v(1+ R2/R1/) so the + I adjstR2 must be very small
But just out of curiosity and for my own edification what voltage is R2 seeing , or how does one calculate I adj R2?

[Biomed]

According to the datasheet I adj is of the order of 100uA and not usually worth considering?

If R1 was 240R and R2 470R, discounting I adj, V out = 3.92V

Taking I adj into account V out = 3.96V

Is it worth taking into account?