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'[OT] More Power Switching Info'
1998\10\23@125807 by Dave Johnson

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Sorry, I should have been more complete in my initial post: This circuit
is powered with 2 alkaline cells, I have a step-up regulator giving me
5V, so any "normal" regulators like the 7805 or others won't work (no
headroom, voltage-wise). I was really hoping to avoid adding another
step-up regulator (they're noisy and inefficient), but maybe that's the
only reasonable choice.

As for the MOSFET: my understanding was that the "on" resistance is still
in the tens or even hundreds of ohms, maybe (hopefully) I'm wrong. But if
that's the case, why do all the analog switch ICs I've been looking have
significant on resistance, don't they use FETs to do the switching?

Dave Johnson

1998\10\23@130941 by Rob

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On Fri, 23 Oct 1998, Dave Johnson wrote:

> As for the MOSFET: my understanding was that the "on" resistance is still
> in the tens or even hundreds of ohms, maybe (hopefully) I'm wrong. But if

As others will likely tell you, MOSFETS can be had for 0.1 ohms turn-on or
less.  Look at International Rectifiers web site or catalog.


>
> Dave Johnson
>

1998\10\23@131154 by Dave VanHorn

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> As for the MOSFET: my understanding was that the "on" resistance is still
> in the tens or even hundreds of ohms, maybe (hopefully) I'm wrong. But if
> that's the case, why do all the analog switch ICs I've been looking have
> significant on resistance, don't they use FETs to do the switching?
>
> Dave Johnson


They use Itty-Bitty Fets, and so they have large on resistance.
I'm using Pmosfets for a buck reg in my battery charger, that have .02
ohms on resistance. National NDS9400A in an SO-8 package.  This is
handling 2A and not warm enough to notice.

1998\10\26@084535 by Brian Watson

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Dave

There are lots of MOSFETS with very low on resistance

Philips PHP45N03LT in TO220 with Ron = 0.024ohms and 5V logic level input.
It costs 1.68 pounds plus tax (UK).
Harris RFP30N06LE in TO220 with Ron = 0.047ohms and 5V logic level input.
It costs 1.24 pounds plus tax (UK).
SGS Thomson BUZ10 in TO220      with Ron = 0.08ohms and Vds = 30V.  It costs 0.6
9
pounds plus tax (UK).

These are just a sample from e Farnell Electronics catalogue, but you should
be able to get these locally, too.

Brian Watson

{Original Message removed}

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