From: Terry Pinnell
Subject: Re: zero-power toggle circuit; was, how to master electronics
Date: Wed, 20 Nov 2002 07:44:14 +0000
References: <3DD39D90.firstname.lastname@example.org> <email@example.com> <firstname.lastname@example.org> <email@example.com>
NNTP-Posting-Date: Wed, 20 Nov 2002 07:44:30 +0000 (UTC)
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Winfield Hill wrote:
>Terry Pinnell wrote...
>> Tony Williams wrote:
>>> ... is it worse for P-channel MOSFETS with a higher
>>> drain-gate capacitance?
>> [snip ]
>> It also looks to me as if the failures are, as you suggest, associated
>> with higher powered MOSFETS, which have higher drain-gate capacitance.
>> [ snip ]
>> Anyway (despite fact that I see Win has sustained his earlier
>> position!), I'm crystallising my original view that the circuit is
>> very sensitive to MOSFET type.
> Did I say you could use arbitrarily-large FETs? If so I retract it.
That's how I understood your reply in news:firstname.lastname@example.org
> I downloaded the BS110 Fairchild data sheet which says "They can
> be used, with a minimum of effort, in most applications requiring
> up to 0.17A DC". I thought we were talking power switches?
"Hey that wimpy part was Wafer's selection. You can try something
more serious like an IRF9540, or IRF9Z34N. Or maybe an FB-class
FET, a real man's part in a SOT-227 bolt-it-in 500W package. :)"
> Wafer's circuit uses rather high resistor values, much higher than
> mine. This shouldn't be completely necessary for a circuit that's
> off when it matters. If it turns on and powers a 10mA load, what's
> the harm in another 0.5mA for the switching circuit? It seems to
> work well enough for Wafer, but halving the R values for small FETs
> would make me more comfortable, and further reducing the resistances
> in proportion to any increased FET capacitances would also be wise.
> Why don't you try that in your model?
OK, will do.
Hobbyist, West Sussex, UK