At 06:45 AM 8/19/2005, Martin Klingensmith wrote: >Dwayne Reid wrote: > > > At 08:54 PM 8/16/2005, Martin Klingensmith wrote: > > > >> Assume there is a transformer with an arbitrary secondary voltage, > >> isolated. > >> Is it inappropriate to run a low-side buck SMPS off of this secondary? > >> It seems to me that it makes no difference because it is already > >> isolated. The fact that the low side is not at the traditional ground > >> level seems irrelevant. The control IC ground potential would be the > >> negative end of the secondary and the positive would be a low power > >> linear housekeeping supply. > > > > > > Your assumptions are spot on. The transformer provides whatever > > isolation it was rated for, the output of the transformer is rectified > > and filtered, the SMPS buck convertor changes the filtered DC with > > lots of ripple into the desired output voltage. > > > > Make sure that the reservoir cap is large enough to ensure the buck > > convertor does not run out of headroom during the low points of the DC > > ripple. > > > > dwayne > > >Hi Dwayne, >I didn't think of how to sense voltage though. The control IC expects a >2.5v voltage error signal. It is unclear how I would do this with a >low-side buck. Any ideas? Actually, what I envisioned is the transformer/rectifier/filter block simply feeding a DC-DC buck convertor. In other words, design the DC-DC convertor as normal. Then feed it from the unregulated supply. dwayne -- Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax Celebrating 21 years of Engineering Innovation (1984 - 2005) .-. .-. .-. .-. .-. .-. .-. .-. .-. .- `-' `-' `-' `-' `-' `-' `-' `-' `-' Do NOT send unsolicited commercial email to this email address. This message neither grants consent to receive unsolicited commercial email nor is intended to solicit commercial email. -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist