On Sat, 2007-06-16 at 22:23 -0400, DJ Delorie wrote: > > Doesn't seem that you gain or loose anything here - assuming the > > switching time is not affected. > > The FET helps because there's an ohmic loss across the diode on the > order of Io*Vf when the switcher is in the off state. The FET has a > lower Von (Vf) than the diode, which reduces this particular loss.
Sorry - I wasn't being clear, I was thinking of the main switching element, not the synchronous rectifier FET. I know I commented on that right before. > You still need the diode, though, in case there's current during the > transitions. Yep, but depending on the exact application - you "Might"(TM) be able to use the synchronous rectifier FET's body diode. Most FETs don't have great characteristics for their body diodes though, as they are essentially a parasitic. [snip] > And choosing caps with higher voltage ratings helps them last longer, > too. I didn't know that for electrolytics, but I can well believe it. I've heard of sizable de-rating need for reliability in rolled-film capacitors used at high voltage. (UPS etc..) Peter C _______________________________________________ geda-user mailing list [email protected] http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
