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From: "Bill Bowden" <**firstname.lastname@example.org*>
References: <3DC3EFA5.email@example.com> <3DC517EB.firstname.lastname@example.org> <3DC57B4E.email@example.com> <firstname.lastname@example.org> <email@example.com>
Subject: Re: zero-power toggle circuit; was, how to master electronics
X-Newsreader: Microsoft Outlook Express 5.00.2314.1300
Date: Thu, 14 Nov 2002 06:07:36 GMT
NNTP-Posting-Date: Thu, 14 Nov 2002 06:07:36 GMT
Organization: AT&T Worldnet
Terry Pinnell wrote in message
> Winfield Hill wrote:
> > A very nice explanation of how the circuit works, thanks!
> > You're right of course. I'm sorry - that's what can happen
> > when a design passes through several iterations on an ASCII
> > computer screen; I should stick to paper for my doodlings!
> > Anyway, I overlooked updating the value of R2, it should be
> > much smaller. In fact one could eliminate that resistor
> > entirely except for the fact it's not nice to blast the base
> > of a transistor with many amps for a microsecond! If we
> > choose say 330 ohms, that should suffice, yeilding a 330us
> > time constant and a peak base current of 20 to 50mA. This
> > is easy on the transistor and insures that the FET's required
> > turn-on gate charge is provided. The 2n4401 can be expected
> > to provide at least 400mA of charging current to the FET gate
> > for at least 100us, that's over 40000nC of charge. A modern
> > IRF540 FET turns fully on with less than 30nC, the original
> > version might require 50nC of gate charge. Larger FETs mayf
> > require up to 250nC, so they can be nicely accommodated too.
> > I'd like to increase R1 to 470k as well.
> > Perhaps Terry can try these new values in his model. Enjoy!
> That sorted it, Win. With R1 = 470 K, it worked fine for R2 in a range
> 330 R (the lowest I tried) to 1K4 K. Toggling failed at 1K5.
> Terry Pinnell
> Hobbyist, West Sussex, UK
Looks similar to a debounced MOSFET toggle switch I did
last year and Win helped me fix it. But it's not zero power and
uses a NPN and one less resistor. Came out to 470K and 220 ohms.
The extra 10uF and 10K and diode ensures the thing powers up
with the MOSFET off.
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