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[aprssig] LM7805 and caps

Mike Miller mike.kc9doa at sbcglobal.net
Mon Aug 27 04:18:36 UTC 2007


Three terminal regulators can oscillate. It is good practice to 
bypass the input and output with something that is effective at 
radio frequencies.

Mike kc9doa

On 27 Aug 2007 at 6:36, Andrew Rich wrote:

> 
> Can someone explain to me why this is so:
> 
> I have been building some projects now that use LM7805 voltage
> regulators.
> 
> This is now the second time I have had issues with a PIC chip not
> running.
> 
> It is only when I add caps to the input and the output that it
> settles down.
> 
> Looking on the CRO, the DC looked noisy.
> 
> I thought that the caps where there to trap AC.
> 
> Do caps on an LM7805 player a larger role ? Is there something
> inside the reg that needs external C ?
> 
> Curious
> 





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