[OZAPRS] LM7805 and caps

[FLECK, Wolfgang]

It is common knowledge that these 3 terminal regulators have a tendency
to oscillate. The capacitors prevent it. They need only about half a
microfarad or so to settle them down. It is also a good idea around RF
gear to have a bit of extra filtering. Say a 0.01mF ceramic in parallel.

Regards Bob VK2BYF

-----Original Message-----
From: Andrew Rich [mailto:vk4tec at people.net.au] 
Sent: Monday, August 27, 2007 6:37 AM
To: Aprssig
Cc: ozaprs
Subject: [OZAPRS] LM7805 and caps

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



------------------------------------------------------------------------
----
Andrew Rich VK4TEC
vk4tec at people.net.au
http://www.tech-software.net



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