At 01:45 PM 3/12/2003 -0500, you wrote:
>Hi Spehro!

Hi:-

>On Wed, 12 Mar 2003, Spehro Pefhany wrote:
>
> > http://www.ti.com  Power Trends, now part of Texas Instruments.
> >
> > e.g. PT78Sxx series, but there are dozens of part numbers.
> >
> > They are NOT cheap, about FIFTY times the price of a 78xx regulator
> > (not counting heatsink). Don't spec these in a volume product if you
> > value your job and are not working for the military.
>
>There's more to cost, -especially- in volume, than just that one part.
>Consider all the cost/space values of possibly leaving the fan out of a
>design because the regulator might be the largest or even only
>(significant) heat producer. 1) fan cost, 2) using a smaller enclosure
>because there's no fan, 3) no fan cutout (molding design/fab costs), 4) no
>fan and associated wiring parts assembly, 5) never having to worry about
>the fan failing (including fail sensor (temp or fan power) and associated
>failure/shutdown hardware/software).

Sure, SMPS regulators are widely used, and quite often appropriate,
just not these expensive pre-packaged subassemblies, except in very limited
cases. A simple SMPS (made from a UCNxx part or whatever) can easily be
cheaper than a linear when you count the factors you mentioned.

>The cost of these power parts will also likely drop like a brick over a
>few years, so take future cost into account too.

If they do not become popular enough they might also be discontinued or
increase in cost. TI is pretty hard-nosed about that sort of thing.
Ask the poor schmucks who designed in their TO-92 current mirrors.
They are gone and there is no substitute or second source.

>Less important of course
>if the life if the product isn't expected to be even that long which is
>all too common today.

Another can of worms, indeed.

>I'm not disagreeing with you, just adding to the perspective.
>
>Have a :) day!

& U2

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

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