[aprssig] LM7805 and caps

[Mike Miller]

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
>