Adjusting the output of S18V20ALV


I’m trying to use the S18V20ALV to generate an 8V output from a 12V input. All I get is 5V on the output no matter how much I turn the adjustment pot. Am I missing something? I’ve got a 100k load resistor on the output. The input voltage is coming from a linear bench power supply.

I’ve got 2 of these units and they’re both acting the same way so I must be missing something simple.

Thanks for any suggestions.


I would try a 1K or lower load resistor. Some regulators do not work well under very light loads.


I am sorry you are having trouble with your regulators. It is very strange that both of them are outputting exactly 5V. (We do not preset the potentiometers on our adjustable regulators to any particular position.) Can you describe how you are measuring the output and post a picture that shows those connections? What is your power supply?

By the way, that regulator should work without a load, so can you try measuring the output without any resistor there?


I might not be back at the office until Monday so I might not get pictures until then.

I’ve tried 2 different supply sources: a benchtop linear power supply and a Lambda switching AC-DC converter. The output of the 2 units aren’t exactly the same but pretty close. One puts out ~5.07V, the other one ~5.13V. I’ve measured the output open-circuit and with the 100k load resistor, no change in the output. I’m measuring the output with a standard DMM.

I’ll post pictures next time I’m in the office.



Just getting back to this issue now. Here are 2 pictures of my test setup. One shows the hookup (input coming from a standard AC/DC converter, load resistor on the output), the other shows the input and output voltages on DMM’s.


And here’s a short video showing my turning the adjustment pot with no change on the output.


The other board I have behaves exactly the same. I think I was somehow given fixed-output boards rather than adjustable boards but I wouldn’t expect there to be an adjustment pot on the fixed boards.



Hi, Dave.

Thanks for posting the pictures and video; I don’t see any obvious issues with your setup. We did some calculations to see if any possible disconnection of the pot (wiper, high side, or low side) could explain an output of 5V, but no luck there, either. At this point, it might just be easiest for us to look at the boards ourselves. Please send us an email at with your order information and a reference to this thread so we can get you an RMA number.


Thanks Claire. RMA email sent.