[OZAPRS] LM7805 and caps

FLECK, Wolfgang wolfgang.fleck at baesystems.com
Mon Aug 27 13:50:49 EST 2007

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

This is now the second time I have had issues with a PIC chip not

It is only when I add caps to the input and the output that it settles

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
reg that needs external C ?


Andrew Rich VK4TEC
vk4tec at people.net.au

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