On Mon, Dec 21, 2015, at 01:17 PM, Gene Heskett wrote:
> The mosfet isn't a problem, nor would a small sig npn transistor, but > power for it is. Not because its needed, but because of the external > powers on-off transients feeding in and causing a few cycles of "on" > before the rest of the circuit is ready. > > That will obviously defeat the purpose unless that external supply is > itself fully floating. I do have a smallish 12.6.ct.12.6 tranny, good > for 200 mills or so, that I can make that psu with, and be completely > isolated from a ground reference except for the capacitance in Cp, and > of course the leakage capacitance in the transformer. But theres no > base thread, so I'm stuck at 500 hertz. It seems to me that the FET source needs to be common to the signal and the load power. Regarding the initial "power up" glitch, that shouldn't happen. The reservoir cap (Cr) needs to be much bigger than the pump cap (Cp). I consider 10:1 as a minimum, 50:1 or even 100:1 can be used if needed. A rough approximation is that if Cr is 50 times Cp, it will take at least 50 pulses to charge it up. That should pretty much eliminate any mis-behavior at startup. -- John Kasunich [email protected] ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
