Olin Lathrop embedinc.com> writes: > Peter wrote: > > To me this sounds a lot like your feedback loops from the pfc and > > from the main switcher are locking into each other and setting up > > some kind of oscillation when there is no load. One way to have power > > being consumed and 'disappear' (no heat), is by transmitting it as RF > > elsewhere. > > He's loosing a few 10s of watts if I recall correctly, which seems very very > unlikely to be radiated. True, but it mostly goes into the attached instrumentation and supplies, not out in the air. Also, the instruments are not to be trusted if they 'see' even a few hundreds of mW of HF in the leads. There are very few digital instruments that are not disturbed by RF/HF injection, and most benchtop supplies with digital readout will display total BS when subjected to unfiltered switching noise from the load. Reading high in this case is rather normal, but some instruments read low or even negative. Estimating input power based on such readings is not a good idea. Some good lab supplies do have a RF warning light on them, though, so the problem is known. After wasting a number of hours on related problems I did bother to do some informal testing with a 10W RF test generator and all the meters and testers I had in the lab at the time. At about 2W output (the instruments were on the wooden floor, in a square series tuned wire loop loaded with a 50R load) *none* of them was reading right. The only one that was somewhat ok was an old d'Arsonval multimeter, but that showed some interesting effects too, likely due to the moving coil protection diodes. FWIW even a usually reliable Fluke meter beeped desperately and showed high volts on an Ohms(!) continuity scale when subjected to this test. At least it did show that something was not ok. Later I got used to the Fluke (not connected to anything on the table) beeping off when the switching circuits I was working on let loose some 'leakage', and used that as a reasonable reliable warning that odd things are happening ... You have to admit that losing a few 10s of Watts is *bound* to heat up something rather quickly, no matter what. Given the power ratings of today's miniaturized parts it would cause some kind of noticeable problem rather soon, if the leakage would be real. Peter -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist