LM117 voltage

[moonstreat]

That I wanted my regular maintenance of 2V to 25V with the LM117, but I can not do the calculations .. the scheme is as follows:


**broken link removed**

In'll 30V Vin, the formula for calculating is: Vout = 1.25 (1 + R2/R1)

Please help me

 

[ronsimpson]

You want 2 to 25 volts.
If R2=0 ohms you get 1.25 volts.
If we choose R1=125 ohms then we have 100 ohms/volt. (simple math)
R2=fixed resistor + pot.
With R2(pot)=0 ohms the R2(fixed)=75 ohms for 0.75 volts. 0.75+1.25=2 volts out.
With R2(pot) set to max you want 23 volts more than 2 volts. 2300 ohms.
first pass:
R1=125 ohms for 1.25 volts.
R2(fixed) 75 ohms for 0.75 volts. (1.25+0.75=2 volts)
R2(pot) 2300 ohms for 23 volts (23+0.75+1.25=25 volts)
You can't find a 2300 ohm pot but you could find a 2000 and scale all other values by 2000/2300.