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5v voltage regulator

I'm using 5v regulator (this one:http://solarbotics.com/products/lm2937/) and it doesn't seem to be working correctly. I'm under the impression that this is how it should work:

  • On the first of the three prongs, I put the positive (red) wire from a 9v battery port thing
  • In the middle prong, I put both negative (black) wires.
  • On the third prong, I put another red wire
  • A black wire from the middle prong and the red wire from the third prong should, when attached to voltmeter, give 5v. Currently it is giving 9v. I have tried switching the positive wires.

Am I incorrect in any of these assumptions? If not, what am I doing wrong? Basically, how do I get 5v from 9v?

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Um... it doesn't sound like you're doing anything wrong. Maybe your regulator is busted? They're pretty tough components, but even the best parts break sometimes. I'd normally suggest checking for shorts or accidental solder bridges, etc, but those would be pretty obvious in this case.

Have you soldered the wires on? Or is this built on a PCB or a breadboard?

I'm just using alligator clips for the moment. It's bizarre, I'm pretty sure it worked before with 6 volts, but I guess it's possible I misread the (analog) voltmeter if it was around 5. I guess I'll try again?

 edit: I tried again, it's definitely not the alligators accidentally touching each other. I've tried switching the positives and it gives 9v either way. I'm guessing it's got to be a problem with regulator, because it should block charge one way like a diode, right? sucks, too, I just got it in the mail from solarbotics.

Not sure about whether the regulator will block current going the wrong way, but it definitely shouldn't read 9V in both directions... yeah I can't think of anything that could cause this to happen except a busted regulator. Maybe there's a more convenient local electronics place you could get some 5V regulators from? Since you're using 9V supply you don't need a low-dropout regulator, and the '7805' family of 5V regulators is very common.
Yeah, I guess I'll have to. Thanks for the help
make sure you have a 10uF cap on the output, or it won't work
The capacitor has nothing to do with the regulator working or not. It is there as a noise filter.

check page 7 on the datasheet, it as to have the capacitor and as to be a low ESR, or it won't work

Sorry, your right.


we have lost our share of time and hair here at work with this kind of thing


I also thought the 10uF cap was for noise filtering, but I have just tried it and the voltage spikes (possibly to 5v?) and then flattens out to 0. I am supposed to attach it in series with the voltmeter in the output circuit, correct?

 also, I tried connecting it in parallel, but that just gives 9v still.