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Help choosing decoupling capacitor

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RoboWanabe

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Hi i need help with a problem.

Im using a 12v input with a Lm7805 voltage regulator to supply 5v to my pic microcontroller.I need help choosing the de-coupling capacitor. The choice of capcitors from maplins are:
Metallised Polyester Film Capacitors: 0.068uf,0.01uf,0.1uf,0.022uf,0.33uf,0.22uf,1uf and 2.2uf :)

Could some one please also maybe explain where the AC ripples come from? I have 2 motors and 1 servo running in the circuit but they run of a diffrent 12v supply. But both these supplys share a common ground?

PLEASE EDUCATE ME!! lol

Thank you.
 

ronv

Well-Known Member
Most Helpful Member
I would just use ceramic capacitors. 0.33 Ufd. on the input and 0.1 Ufd. on the output is what the datasheet suggests.
The capacitors add stability to the regulator as well as ripple reduction.
 

RoboWanabe

Member
Hi again i tryed to get the ceramic capacitors but they didnt have any in stock and the only ones they had were metallised polyester Capacitors. 0.47uf and 0.1uf will these be ok or am i just best waiting for the ceramics to come in ?

Thanks again :)
 

audioguru

Well-Known Member
Most Helpful Member
Why don't you buy electronic parts from a real electronic parts distributor who has plenty of parts in stock?

I think Maplins is like RadioShack here (they are gone now). They sold cell phones, kids electric toys and a few over-priced very old electronic parts.

You have Farnell over there. Here we have Digikey, Newark (also now owned by Farnell) and many more.
 

RoboWanabe

Member
hmm i find maplins usually ok for things like this except on this occasion. but ur right i should go to a specific vender. I could realy do with confirmation on this today as i would love to solder them in and move on ??

PLEASE HELP !!!!!!!!!!! LOL
 

audioguru

Well-Known Member
Most Helpful Member
The voltage regulator will work fine with metallised polyester capacitors. Mount them close to the pins of the voltage regulator.
 
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