7812 regulator stability

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#1
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Comments and opinions are invited relating to stability of 7812 regulator on a longish ( say few feet ) umbilical from rectifier filter.

Specifically are they likely to break into oscillation and burn up and die?

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Any three terminal regulator that is separated any distance from its input voltage source by more than a few inches should have a 0.33 to 0.47uF cap tied directly from the input pin to the regulators ground pin. This removes the inductive input effects of the long line feeding the regulator and allows for a better transient response. Likewise, a minimum of 0.1uF cap should be added the the output of the regulator to improve stability and transient response. You will not burn up or destroy the regulator if you do these two things.

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Interesting coincidence... Phil ("ProfiCNC") told me this evening that he was called in to investigate the unexplained destruction of numerous 3V3 regulators fed from a USB cable 5 volt source. All fixed when a cap was added to the input of the 3V3 regulator.

Ross McKenzie ValuSoft Melbourne Australia

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I never saw this happing but I always follow the rules specially when the regulator is far from the power source. Caps, low pass filter (lc)...

Regards,

Bruno Muswieck

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You can see the effects of this issue over at DIYDrones...
http://diydrones.com/forum/topic...

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www.proficnc.com
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