# efficient 3.3v linear power supply questions.



## ganesht (Oct 13, 2008)

I need a 3.3v regulated power supply; at first i was using a two linear power supplies; one to drop the 14-12v down to 5 then the second down to 3.3 with decoupling capacitors between each component. The i didn't realize how much heat the 7805 would create; so for version 2 i want to use a 5v buck converter to drop it down to 5v and then keep the 3.3v regulator (lm1117); my question is will the 1117 be able to output a clean 3.3 supply when its being supplied with an input voltage ripple?


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## sonikaccord (Jun 15, 2008)

garbage in...you know the rest.

You could clean up the input signal with filter caps.


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## UMD_Jesse (Apr 26, 2012)

What you need is an LM2576t-3.3 I just built one of these and let it run for 2 days at 14 volts input. Steady 3.3 volts out and NO heat what so ever. Just follow the schematic in the spec sheet exactly and it will work. Let me know if you have questions.


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## ganesht (Oct 13, 2008)

I needed a 5v output also so i ended up using a 5v buck followed by a 3v buck with the necessary decoupling cap and inductors, i haven't been able to find an o scope to look at the output ripple, but the pic running off the 5v buss and the airport express on the 3v buss seem to be happy. My concern (and reason for this thread) was if the voltage ripple would introduce extra noise into the system, but as far as i can tell there is no added noise to the signal.


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