On Monday 21 December 2015 13:43:23 John Kasunich wrote: > 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. > Absolutely. It could even be a std 2n2222 for that matter, and the shutdown lag wouldn't be quite as great as with the fet. OTOH, that would all depend on the needed initial bias to make the fet conduct too.
But in the context of discussing the micro-coulombs per pulse pumped by Cp, should we not discount it somewhat because of the limiting source resistance the BoB's output stage represents? Or are we assuming a Cp small enough that at 1 millisecond at each voltage level, t=rc is essentially infinite and Cp is fully charged to whatever differential voltage is available? Also, and I am not sure I have two of them, and I know I don't have 4 for both circuits, so I expect I should order a small bag of schotkey diodes, which would raise the potential output voltage by approximately an additional volt. > 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. I don't believe the junk box network I put together for the vacuum is more than 3 or 4/1. Its driving a junk box to-220 of some sort, which is in turn pulling the 24 volt coil of a DPDT P&B octal plugin relay, whose contacts are paralleled in deference to the 6.5 amps running (at normal air flow, my lashup could even be higher because nearly all the plumbing but the radiator hose is nice smooth interior 1.5" PVC, and that 6.5 is probably measured with the 1.125" corrugated hose normally used. That stuff, while handy as a vac hose, is very high internal turbulance & a good flow restriction) My "nap" lasted about 4.5 hours! I must have really been behind. Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Some mill pix are at: Genes Web page <http://geneslinuxbox.net:6309/gene/GO704-pix> ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
