Russell McMahon wrote... >My real results AFAIK are say 85% at Vin =3D 15 and 55% say at Vin =3D = 200 v for >a 10 volts out say. at 600 mA. SIX HUNDRED MILLIAMPS?????? Good grief, no wonder our mileages vary! We've got an "apples and oranges" problem here- in fact, several of them. In your original design challenge post, you solicited design ideas for a switching regulator that would output "a few tens of milliamps" at five volts for operating a PIC and its associated circuitry given a power source whose voltage could range up to 50 volts or more, and doing so with "reasonable" efficiency. And it was at "several tens of milliamps" (20 mA, specifically) that I performed the simulation of your proposed circuit which formed the basis for the comments in my previous post. Frankly, it didn't work worth a darn at those levels, which are the conditions under which I assumed you intended the circuit to operate. I was puzzled by this, hence my request for measurement data showing what efficiency you had actually obtained in practice. You've provided the data, but it refers to operation WAY outside the range which you'd earlier indicated was of interest- at an output current of 600 mA instead of 20 mA. Do you have any efficiency data for this circuit operating at=20 Iout =3D 20 mA? The other source of confusion is, which of your circuits are we talking about? The one where the MOSFET gate is turned off only by the 100K bleed resistor? Or the one with the active turn-off circuit (QBUK3 and DBUK1, in diagram picbful.gif)? My comments referred to the former while yours, I take it, refer to the latter- or perhaps to some other variant of one of these. Which is it? I was intrigued by your design challenge because that's what designing a low-current switching regulator is: a REAL challenge. I've designed a few in the past, including some that had to power the innards of a 2-wire, loop-powered 4-20 mA process transmitter- an application in which the absolute maximum available operating current is only about 3.5 mA. It ain't easy. An output current of 600 mA, though, is right in the middle of the "sweet spot" when it comes to switching regulator design. The world is absolutely awash in application notes which describe how to design switching regulators with outputs ranging from a few hundred milliamps up to a few amps; and there are literally dozens of different ICs designed to do the job and most of them do it very, very well. The 200 volt input does, I'll admit, pose a design challenge; but it isn't one that's of much personal interest to me. I don't like HV; it hurts! Incidentally, I re-simulated your circuit with QBUK3 and DBUK1 included to improve the MOSFET turn-off speed. After playing with component values a little, and loading the output to 500 mA, I got simulation results that were more or less consistent with the efficiency measurement data you cited. I still don't like the Zener current, though. Someday, that's going to come back and bite you. Dave -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu