I have a cheap little generic voltage regulator board which should allow me to select both the output voltage and the maximum output current, but I can't get it to limit the current properly. The board is based on a LM2596 and looks very similar to this one:
and as you can see it only has two potentiometers, can't get much simpler. So what I have is a power supply feeding the left-hand side with 7.5v and what I'd like is 6v out of the right-hand side up to a maximum output current.
It's immediately clear that the left-hand potentiometer controls the output voltage, and I can select 6v output without problem. Note that there is a red/green LED on the right, and with just a voltmeter across the output, the LED is green (apparently indicating 'no load').
Now I'd like to limit the current, but whichever way I turn the right-hand potentiometer, the output current is unaffected. I can turn the potentiometer apparently endlessly in both directions, and never reach a stop - which is a little surprising. At first I thought the potentiometer might be broken or not connected at all, but there is a point where turning the potentiometer changes the LED from red (load) to green (no load). But the output current flowing through my load doesn't change at all, which I can't understand. Also the input current is not affected.
I'm sorry this sounds like such a trivial problem to solve but to put it in concrete terms, I have 7.5v coming in, 6v coming out, and a 50 ohm load. So it's trying to draw 120 mA and I'd like the regulator to limit it to say 90mA. I'm assuming that if I turn the potentiometer in the correct direction far enough, the output current will be limited to 90mA and the output voltage will drop accordingly. Instead I see the output current constant all the time, no matter which way I turn the right-hand potentiometer - and as I said it seems to turn endlessly. Am I not understanding the way this current limiting should work, or have I got the wrong kind of board for what I'm trying to do? Also, what's the significance of the LED changing from green to red even though the output current doesn't change?