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From: "Helmut Sennewald"
Subject: Re: zero-power toggle circuit; was, how to master electronics
Date: Tue, 19 Nov 2002 22:58:09 +0100
References: <3DD39D90.email@example.com> <firstname.lastname@example.org>
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"Terry Pinnell" schrieb im Newsbeitrag
> Terry Pinnell wrote:
> >By bad luck my initial choice of MOSFET wouldn't toggle at all. But
> >subsequent tests with a variety of types gave surprisingly
> >inconsistent results. I've shown my test circuit and results at
> >Given that my simulation of Win's earlier circuit (using a similar
> >button-pressing section) seemed 'robust', I'm puzzled why these are
> >relatively erratic. Is it a flaw in my circuit or interpretation? Or
> >is the circuit itself genuinely sensitive?
> Anyone able tp look at this yet please? Win? Wafer? Jonathan? Maybe
> Helmut Sennewald or Mike Engelhardt could try it in SWCAD III?
I analyzed(simulated) your circuit with SwitcherCADIII.
The circuit switches on and off as required, even with the IRF9513,
when you decrease the feedback resistor R2(e.g. 100k).
This feedback resistor defines the holding gate voltage.
The old IRF9513 has a much higher on resistance than the other two
mosfets you used successfully. I measured 1V voltage drop above this
mosfet with a 10 Ohm load(=0.9A).
Accidentally, you designed not for worst case Vgs_th(2N7000) and
You are too close to the typical threshhold voltage of the 2N7000.
With some mosfets it would work in reality and with some not.
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