Pololu adjustable 9-30V step up/step down voltage regulator S18V20AHV #2573


I recently purchased a few of these to use in a project I am developing at work but for some reason the output voltage can never rise above 8.5V with 12.2V input. This in itself is curious because the unit is meant to regulate voltage between 9 and 30V in/out.

Adjusting the adjustment screw (which is profoundly difficult by the way) doesn’t seem to make any difference at all.

The unit gets very hot and I am cautious of destroying it.

The load is a 12V halogen light which can vary as its temperature varies. The idea is to keep voltage at a constant 12.2V and therefore brightness constant, for scientific applications, regardless of the temperature/resistance of the light.

Why would this be happening? How can I increase the voltage?



What’s the current?

Set the voltage with no load and remember to remove the screwdriver from the adjustment, because the screwdriver itself changes the result.

Once you set the voltage to 12.2V, try it again with the halogen lamp.

Determine the specifications of the lamp and measure the current ramp; for example a 10W lamp will draw 820 mA once stable, and about 3A briefly on connection. A 50W lamp will draw 4A once stable, and about 16A briefly on power up.

If the lamp is demanding more current than the regulator can supply, then it mightn’t be starting up properly, and you’ll see a lower output voltage.

You may also be triggering output current overload.

The unit has thermal shutdown at 165 degrees C, so you can run it hot, but I agree, it’s not good to do that too much; the thermal cycles cause damage, and you have to get rid of that heat somewhere.

I presume you’ve looked at the specs?

If you need constant brightness, you could use an optical or power feedback rather than voltage regulation.

Thank you for your reply.

After checking the specs I figured out this was not suitable for my needs as I need to output at least 12.2V, 35W to drive the lamp.

I was able to use the remaining pair for another purpose though, so everything is good.