Log to linear potentiometer

Hey guys,

I made an adjustable power supply based in an ATX PSU and a circuit I found on the internet.
Works fine but there is a little problem, I only have a logarithmic potentiometer which makes the voltage variation too abrupt. Of course you will say, go and buy a linear one, I will do it, but there are no stores here where I leave, I will have to put an on-line order and wait a couple weeks.
I would like to get this working in the meantime, so I'm wondering if it is possible to convert the logarithmic potentiometer in a linear one, or to get some similar behavior at least.
Tried attaching a resistor between the wiper and the other leg (googled that) but didn't notice any change.
Anything else I could try?

Thanks in advance.

Converting LOG pots to liner:-
http://www.geofex.com/article_folders/potsecrets/potscret.htm

Grumpy_Mike:
Converting LOG pots to liner:-
The Secret Life of Pots

Thanks, probably is that I don't get it right, but there I can only see linear to log, but not the other way around which is what i'm looking for.

Jay98:
Thanks, probably is that I don't get it right, but there I can only see linear to log, but not the other way around which is what i'm looking for.

if you wire the parallel resistor as anti-log and apply it to a log pot, any ideas what you might get

wire the parallel resistor as anti-log

What does that mean?

@mike

Converting LOG pots to liner:-
The Secret Life of Pots

How big is your bag of tricks.

LarryD:
@mike How big is your bag of tricks.

It is about 12K. Plus 40 years in the game :wink:

Something I forgot to say I’m using only 2 terminals of the pot, I think this would be “as rheostat”.
Not sure if the conversion is still possible.

You could use a spare op-amp in lin/log setup, and feed it with a DC signal from your pot.

If my memory serves me right, I believe such a setup is called a compressor, often used in oldtimer Hi-Fi building blocks.

Jay98:
Something I forgot to say I'm using only 2 terminals of the pot, I think this would be "as rheostat".
Not sure if the conversion is still possible.

Fantastic, I love solving problems only to find the problem is nothing like what was originally stated, not.

Two things to try.

  1. Swap the fixed end of the pot with the other fixed end. That moves the response over to the other end which might be more in the area of control you are interested in.

  2. Add a series resistor again to shift the active area of the pot's response.

Thanks Mike, but already tried that with no luck.
About the resistors tried 1K and 4K7 (pot is 10K) looks the same for me.
Switching the pot legs doesn't seems to make any difference either.

BTW, this is the circuit

but already tried that with no luck.

Luck does not enter into it. You did not use the correct values of resistors.

Now this is like getting blood out of a stone.
What voltage range do you want the regulator to output?
The narrower this is the finer control you will have over it.

Don't just guess the value of the resistor calculate it.

Grumpy_Mike:
What voltage range do you want the regulator to output?
The narrower this is the finer control you will have over it.
Don't just guess the value of the resistor calculate it.

Thank you.
It can handle 1.2V-10.5V
I was just trying because I don't know exactly how to calculate the right value. :fearful:

If you read the data sheet it will tell you how to calculate this resistor.