OT - power supply problem

[docwisdom]

OT, but I figured if anyone knew, you guys would.

I have had 2 "wall wart" power supplies with this phenomenon thus far.

When first purchased, my 12 volt 1 amp power supplies would pump out 12 volts when hooked up to a volt meter. I started noticing that on the output side of my voltage regulator, I was getting 8.7 volts instead of 5! So I checked the wall wart again, and it was pumping out 22.8 volts!!!

So is this a problem I am causing, or does this happen to "wall-warts" sometimes?

I am using a LM7805 to produce the 5v from the input source and I have a polarized cap on the output side.

[Bruce]

Most wall-warts are unregulated, and will output more than the rated voltage
until you place a load on them. The LM7805 should still work just fine with this
however since most flavors are rated up to around 35V MAX input.

22V input shouldn't do much more than make your regulator run much hotter. It
should still work fine.

Are you 100% sure you don't have an LM7809 stuck in there, or maybe have
your LM7805 wired in backwards? 8.7V out from an LM7805 is not good.

[docwisdom]

Thank you for making me go back and look into this problem deeper. It turns out it was stupid user error. A mistake in my multimeter settings.


cheers
-brian