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 -- 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