Let's Make Robots!

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?

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.

yeah, everything works. thanks everyone!

 

I just gotta solder everything together... and then I'll probably have more questions 

sorry to double post, but if I get a 'standard'' 5v regulator (for example, this one from radioshack: http://www.radioshack.com/product/index.jsp?productId=2062599 ) , do I need capacitors? I've pretty much written my first one off as broken. 
god old 7805, it doesn't need the caps, but it might be a god idea to use them, just for cleaning up the power
I've never had a problem using a 7805 without smoothing/filtering caps when running off batteries, but I they're usually a good idea anyway, since they don't take up much space. Especially useful if you've got a noisy power supply (like some wall adaptors can be), sensitive circuit parts (poorly isolated oscillators, radio frequency subcircuits), or circuit components that can generate noise or power spikes (motors and inductive parts are the most common).
alright. thanks! I probably will use a capacitor, it's just nice to have to worry about complicated circuit designs and what not... anyway, I'm going to radio shack right now and will see how it works.

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. 

Right

It migth be that your capacitor is not Low ESR, you can also try to conect a capacitor in series with a low value resistor to the output of the regulator, like this

LM2937.png

 

 and also try, connect a resistor greater than 1K in parallel with the output capacitor, this little suckers some times don't like to work with no load.

wait, should there be a cap on the input circuit too? I have to confess I don't really understand that diagram. Do all the little arrows go to the ground?

yes, and yes.

The little arrows are the ground simbol

shouldn't the ground be common?