power supply ripple and NMOS

Martin Hodge

I'm experimenting with switching power supplies, and have been able to produce a circuit that can supply 5VDC @1A from ~28VDC. What I haven't been able to glean from Google searches so far, is if 20mV P-P ripple @ 30kHz on a 5VDC PS is considered acceptable. The target application is a vintage 5-1/4" floppy drive controller board (an Atari 1050) with lots of NMOS ICs and analog. The original PS used linear vregs (7805 & 7812) which generated lots of heat.

Phil Pilgrim (PhiPi)

20 mV sounds really good to me. I can't see how it would cause a problem. I've worked with switching supplies having up to 100 mV P-P ripple without issue.

-Phil

jmg

Martin Hodge wrote: »

I'm experimenting with switching power supplies, and have been able to produce a circuit that can supply 5VDC @1A from ~28VDC. What I haven't been able to glean from Google searches so far, is if 20mV P-P ripple @ 30kHz on a 5VDC PS is considered acceptable. The target application is a vintage 5-1/4" floppy drive controller board (an Atari 1050) with lots of NMOS ICs and analog. The original PS used linear vregs (7805 & 7812) which generated lots of heat.

because the original design used Linear, that will be what they tested with.

You can always add additional filtering, if you think this is going to challenge the FDC.
- either an LC filter stage, or a low drop out linear regulator, and set the SMPS just above drop out.
or retro-fit low impedance Caps to the 5V boards, and use the wire impedance, perhaps with a clip-on ferrite,as part of a somewhat hidden filter.

Martin Hodge

Thanks for the input. I'll keep tinkering knowing that I'm not way off base.