How to smoothly adjust the output voltage on lm317t or lm338t?

Question

Electronics

I assembled a voltage regulator according to the scheme:

I don’t have a 5K variable resistor. I replaced it first with 10K, then with 4.7K. It doesn't regulate properly. Up to 30 percent regulates from 1.3 to 12v with a penny at the output (at the input 13 with a penny), and the remaining 70% of the resistor's turnover does nothing. So what is the value of the variable resistor needed to smoothly control the output voltage?

Answer 1

Here's the datasheet, page 8. The LM tries to keep the reference voltage at r2 in your circuit around 1.25v. The formula for calculating the output voltage from the resistor values ​​\u200b\u200bis on the indicated page. Pick up a couple of resistors, from those that you have, so that they cover the desired output voltage range.
https://static.chipdip.ru/lib/142/DOC000142745.pdf