determining the voltage of a electrolytic capacitor for a voltage regulator?

[Sulla]

I am trying to build a voltage regulator circuit. 12V in and 5V out. I am using a 7805 regulator with a .33uF capacitor and .1uF capicitor. I am having trouble figuring out what voltage I need for the capacitors.

If I am getting this right, I need a .33uF 12V capicito andd a .1uF 5V capacitor, right?

Here is a simple diagram of the circuit:
http://snesdev.antihero.org/wp-content/uploads/2008/03/lm7805.gif

 

[tim]

The 7805 is not rated for 112 V input: http://www.datasheetcatalog.com/datasheets_pdf/7/8/0/5/7805.shtml.

I think you want Ci and Co voltage rating to be at least 150% of the input and output voltages (i.e. the difference pin 1 or 3 and ground respectively) to provide an adequate safety factor.

 

[Sulla]

The 7805 is not rated for 112 V input: http://www.datasheetcatalog.com/datasheets_pdf/7/8/0/5/7805.shtml.

I think you want Ci and Co voltage rating to be at least 150% of the input and output voltages (i.e. the difference pin 1 or 3 and ground respectively) to provide an adequate safety factor.

Oh, crap, I meant 12V input. First post fixed.

 

[tim]

Oh, crap, I meant 12V input. First post fixed.

I'd still go for a 50%-100% safety factor with the voltage ratings. So, instead of 12V and 5V, I'd go for 24V and 10V.

 

[exoray]

I need a .33uF 12V capicito andd a .1uF 5V capacitor, right?

For caps anything rated equal or higher to the voltage you are using... For such small caps like .33uf and .1uf you can even go way high like 50 or 100 volt ones and still maintain a small size...

In short for say a 12 volt circuit a .33uf 25 volt is just as good as a .33uf 1000 volt, and even a .33uf 16 volt is the same...

 

[Sulla]

Thanks everyone!