Most likely failures on power supplies are with the power components. Failure of the pass transistor in a linear supply is likely to result in overvoltage at the output, while failure of the switch on a switchmode supply will blow the fuse instantly.
It is been my experience (after 30 years in the field) that a properly designed switchmode supply is at least as reliable as a linear supply of the same output power, if for no other reason than the lower dissipation and resulting reduced failure rate. By using integrated controllers with lots of protection features built-in, switchmode supplies tend to be smarter than linear ones, and their failures tend to cause fewer damage to other circuits. Of course, your mileage may vary... Didier KO4BB > -----Original Message----- > From: [email protected] > [mailto:[email protected]] On Behalf Of Robert Atkinson > Sent: Monday, June 01, 2009 2:46 PM > To: Discussion of precise time and frequency measurement > Subject: Re: [time-nuts] Thunderbolt - any negatives ? > > > Most switch mode power supplies actually run a voltage > doubler on the input when running on 110V. This puts over > 300V across the transformer and switch. Also the regulation > loop crosses the isolation barrier introducing more failure > points that can result in overvoltage. > > Robert G8RPI. > > --- On Mon, 1/6/09, [email protected] <[email protected]> wrote: > > > From: [email protected] <[email protected]> > > Subject: Re: [time-nuts] Thunderbolt - any negatives ? > > To: [email protected] > > Date: Monday, 1 June, 2009, 6:17 PM > > Hi there, > > > > A switcher has much more stresses on the components, since > it usually > > switches the primary side rectified 110/220V high-voltage across a > > transformer. > > Thus the switching FET has to be very high voltage capable (about > > ~170V DC in the US), and the second component under stress is the > > primary high voltage capacitor, because it sees a very fast AC > > switching current on it (current draw is on when the FET is on, and > > off when the Fet is off). Also there has to be a fast > snubber network > > to prevent the back-emf from destroying the primary Fet with > > over-voltage. > > > > A linear supply has none of these fast current/voltage > transients on > > it, only a couple of diodes switching the 60Hz secondary onto a > > capacitor at low voltage. > > > > A secondary concern is thermally induced stress, switchers will > > usually be packed into a very small enclosure with very high power > > capability/density. > > This is not possible for linear supplies, since the > transformer size > > will usually determine overall sizing. Compare a Laptop > power supply > > size (usually these have between 40W and 90W rating!) to a similar > > rated linear supply. > > > > bye, > > Said > > > > > > In a message dated 6/1/2009 09:48:29 Pacific Daylight Time, > > [email protected] > > writes: > > > > Is there something I don't understand in this area? What makes a > > linear supply more reliable than a switcher? > > > > My first guess would be a switcher would be more reliable > because it > > would run cooler. > > > > That's probably assuming the same amount of design effort which is > > probably not a valid assumption if I'm comparing a brand-X linear > > with a brand-Z switcher. A quick glance at the general > construction > > might give a better answer. > > > > > > _______________________________________________ > > time-nuts mailing list -- [email protected] To unsubscribe, go to > > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > and follow the instructions there. > > > > > > > _______________________________________________ > time-nuts mailing list -- [email protected] To unsubscribe, > go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
