Hi The most common thing to miss on decoupling a switcher is that both the output *and* the input will generate crud that sprays all over the place. Series L on both the input and output are a really good idea. Microhenry (as opposed to milihenry) chokes are generally good enough. Values are dictated more by board space than anything else. 22 uH is not a bad starting point. A SRF above 3 MHz would be a good idea :)
Bob > On Dec 4, 2016, at 3:14 PM, John Ackermann N8UR <j...@febo.com> wrote: > > That's a very good point... the design I'm testing the regulator in has a > fair bit of C filtering, but no series L. > > On 12/04/2016 02:45 PM, Chris Albertson wrote: >> Surprisingly good as a drop-in replacement. >> >> Question: Suppose you are doing a new design and had space on the PCB for >> one more small passive part. I wonder how the performance of the switcher >> with an LC filter compares with the 7805. Yes, I think this is fair. It >> is a trade off, It costs me one more inductor but I gain hugely reduced >> power consumption and heat. >> >> Or stated another way: You have shown the noise difference for drop in to >> existing circuit. What about two roughly equivalent new design circuits? >> How much to we pay in dollars and complexity to get equivalent noise? >> >> Thanks a lot for this work. Headed over to eBay right now.... >> >> (My application uses LiPo battery and needs to have stable voltage as the >> battery drains but my current solution is noisyand those 78xx chips waste >> far to much power. ) >> >> On Sun, Dec 4, 2016 at 10:50 AM, John Ackermann N8UR <j...@febo.com> wrote: >> >>> I found a cute little switching regulator that's a drop-in replacement for >>> an LM7805: http://www.ebay.com/itm/261243604047 >>> >>> I got a couple to play with, mainly to see how bad the noise would be. >>> Here are spectrum analyzer and PN shots comparing a cheap surplus OCXO when >>> driven by a regular 7805 and by the switching replacement. >>> >>> The switching frequency is supposed to be 2 MHz but you can see that it's >>> more like 2.4 MHz. Whether this performance is sufficient for any >>> application is up to you. It sure runs a lot cooler than a 7805, though! >>> >>> John >>> >>> >>> >>> >>> _______________________________________________ >>> time-nuts mailing list -- time-nuts@febo.com >>> To unsubscribe, go to https://www.febo.com/cgi-bin/ >>> mailman/listinfo/time-nuts >>> and follow the instructions there. >>> >> >> >> > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.