[OZAPRS] LM7805 and caps

[Ray Wells]

Ian ZL1VFO wrote:

>>Message: 4
>>From: "Andrew Rich" <vk4tec at people.net.au>
>>Subject: [OZAPRS] LM7805 and caps
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>>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 ?
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>The little beggers sometimes take off and oscillate without any C
>around them.
>
>I usually put 10-100uF & a 0.1uF ceramic across the input to gnd, and
>several uF and another 0.1uF ceramic across the output. Might be a bit
>of an overkill, but I'd prefer these things didn't take off and cause
>wierd effects in uP or other logic circuits...
>
>-Ian ZL1VFO
>
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My Kenwood TS430 developed severe (S9+) interference at around 455khz. 
Turned out to be a dried out electro associated with a 78L08 regulator. 
Difficult find, easy fix.

Ray vk2tv
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