quick POT question

Other Hardware General Electronics
1

Hi Guys.. I am making a home made power supply and using the buck converter and POT to supply variable voltage to components.

I have one of these:

I removed this existing 10k pot:

and replaced with this 10k pot (easier to mount and use in power suppy):

The problem is that from about 50% to 100% its full 12v (like it doesnt do anything).. like it only really uses half of the distance to make changes but the other half does nothing and stay at current voltage..

how can I get the full range from the POT so it accurately shows changes from 0-100%?

thanks!!..

Pete

2

maybe try connecting it backwards to see if it changes or take it off and test with a multi meter..

Pot could be faulty

3

The pot in that converter is a 10 turn helical pot. You are replacing it with a 270 degree pot.
What dead range does the helical pot have?

4

Pot ratings have a huge margin. You need to measure to know how each one actually works.

5

Did you check if you got the B-version. 10kB.
Not the A, which is log.
Leo..

6

The buck regulator is behaving correctly with a 10k pot - when your input voltage is 12 volts. The board is designed for a 40 volt input so with 12 volts in, the pot stops changing the output voltage when it gets to about 1/3 of the total rotation.

If you never intend to put more than 12 volts on the input, you can expand the range of the pot. There is a 330 ohm resistor that is connected between pin 4 of the LM2596 and one end of the 10k pot. It's mounted between the pot (where it had been) and the tab of the 2596. It's probably marked 331, it's the black part, the brown chip below it is a capacitor. Remove the 330 ohm and replace with a 1k part, a 1% metal film part would be best as it directly affects the output voltage. That will result with an output max of about 13 volts so while it does not use the full 100% of the pot range, its waaaay better than what you have now.

If you want some other voltage range, consult the LM2596 datasheet, it provides the equation for output voltage.

7

You didn't use a non-linear audio volume control pot, did you?

EDIT: OOPS! Sorry Wawa, I lurched in too quick. :-[

8

Make sure the leads to the pot are nice and short, tight layout is needed in DC-DC converters, the
pot is in the feedback path. If the wires have to be long best to use shielded cable, with the ground
side of the wiper as the shield.

9

avr_fred you are the man.. I replaced that 331 with a 1k resistor and its works great.. awesome resolution and it works for pretty much the entire dial!!! thank to all for your comments!!