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Topic: Voltage regulator (Read 694 times) previous topic - next topic

Yoduino

Hey guys, so I basically need a voltage regulator that can output about 3.75V. I have a 3.3V and 5V voltage regulator http://www.sparkfun.com/products/526 and http://www.sparkfun.com/products/107 as well as a few capacitors. I am inputting voltage with a 7.4V LiPo battery so I basically need to step that down to around 3.75V although I assume 3.3V would be ok. I tried to solder something together using a L4940V5 and two capacitors like the attached image but it did not work very well because the voltage was not constant and I just need some help to make something that works well and is relatively simple. Essentially I need something like this: http://www.dimensionengineering.com/AnyVoltMicro.htm but I don't want to spend the $20 because I already have some components and I sort of need to make this by tomorrow.

Yoduino

Sorry, I forgot to mention that a 100uF capacitor was added between the input terminal and ground and a 10uF capacitor was added between the output terminal and the Arduino.

JoeO

LiPo batteries are not something to fool around with.  I have heard of many fires with them.  Buy the correct charger for the batteries you are using.  Read the part about charging in the link below.

http://en.wikipedia.org/wiki/Lithium-ion_polymer_battery

zoomkat

Maybe a stop at Radio shack.

http://www.radioshack.com/product/index.jsp?productId=2062601
Consider the daffodil. And while you're doing that, I'll be over here, looking through your stuff.   8)

James C4S

Generally regulators have a minimum load requirement before their output is stable.  You might try a load of a 10K resistor just to get some current flowing.  This combined with the relatively large capacitors you are using could be keeping the regulator from stabilizing its output.  (The datasheet only recommends 0.33uF on the input and 0.1uF on the output.)


Of course if your goal is 3.75V then zoomkat's suggestion is best of all.  Just go straight for an adjustable regulator.
Capacitor Expert By Day, Enginerd by night.  ||  Personal Blog: www.baldengineer.com  || Electronics Tutorials for Beginners:  www.addohms.com

Yoduino

Thanks for the help, I ended up using an LM7805V http://www.sparkfun.com/datasheets/Components/LM7805.pdf without any capacitors and although it gave a higher voltage than I had originally wanted, the servos that I had hooked up to my pro mini were working fine, so I guess the simplest way in this case was the best.

pwillard

Simplest is not the best if it's wrong.

Quote
without any capacitors


Nowhere in the datasheet does it say that capacitors are OPTIONAL.

Yoduino

I 100% agree with you but after significant testing with the recommended .33uF and .1uF capacitors, I determined that I did not need them. I know that my solution might be somewhat unconventional but it works and thus I am happy, but yes it is "wrong". 

Graynomad

If you want to make your own get an adjustable regulator, then you can have whatever voltage you like.

_____
Rob
Rob Gray aka the GRAYnomad www.robgray.com

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