On 6/27/08, Xiaofan Chen wrote: > On Fri, Jun 27, 2008 at 4:54 AM, Olin Lathrop wrote: > > There is nothing in basic physics that says this needs to be true, which is > > why it isn't. This may be true for some types of converters with particular > > properties, but to say this broadly applies is just wrong. > > There is. I've done theoretical steady state analysis, albeit simplified, > to show that at very low and very high duty ratio, the buck > converter efficiency will suffer. More theoretical analysis here: http://scholar.lib.vt.edu/theses/available/etd-03092002-004940/ Read Chapter 2 about the low duty ratio's effect to the multi-phase buck converter. It applies to single phase synchronous buck converter as well. The above assertion is about normal single stage buck converter without a transformer or coupled inductor. If a transformer is involved (which changes the effective duty ratio), high input voltage can actually be an advantage. Xiaofan -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist