Re: PC power supply-- why not stynchronous rectifiers?


Rene Tschaggelar wrote:
Tim Shoppa wrote:
And second of all, there is probably only 15 cents profit in each power
supply sold, and that has to be split between manufacturer,
distributor, etc. Anything you suggest that makes the PS be cheaper,
hey they'll do it. In fact they're probably already doing it :-). Those
low Rds MOSFETs probably would add a dollar or two to the cost, and did
I mention this is a very cost-sensitive market?

There are real markets for efficient robust switching power supplies,
but not in generic PC-clones.

There are those PC power supplies that are included
with the case and cost 40$, and there are those low
(acoustic-)noise power supplies you buy for 150$
after fearing to become deaf from the cheap ones.

Rene

Rene Tschaggelar wrote:
Tim Shoppa wrote:
And second of all, there is probably only 15 cents profit in each power
supply sold, and that has to be split between manufacturer,
distributor, etc. Anything you suggest that makes the PS be cheaper,
hey they'll do it. In fact they're probably already doing it :-). Those
low Rds MOSFETs probably would add a dollar or two to the cost, and did
I mention this is a very cost-sensitive market?

There are real markets for efficient robust switching power supplies,
but not in generic PC-clones.

There are those PC power supplies that are included
with the case and cost 40$, and there are those low
(acoustic-)noise power supplies you buy for 150$
after fearing to become deaf from the cheap ones.

Rene

China's amazing. When the power supply in my new-bought Compaq died
after four month's service, I got an improved replacement, *new*, for
$13 from a clone vendor at the TRW swapmeet.

I'd cracked open the failed unit and even ordered $15 worth of fix-it
parts from DigiKey, but ultimately deemed it not worth saving.

The whole thing seemed very nicely done electrically, using
name-brand parts from vendors we know, and including a 900v 8A MOSFET
switch. Shrink-wrap, hot glue, and tie-wrap were lovingly and
liberally applied, as if the parts receiving these were family members
needing protection from vibration, voltage. So far so good.

The layout, however, can kill an otherwise good design, and it killed
this one. It was a flyback with smart fan control, making it very
quiet. I liked that, but, in retrospect, it was a defect: the fan
control failed to deliver enough air, and switching-transistor-plasma
spewed. The 85c-rated bulk filter caps were next to and _glued_ to the
main switch's heatsink. Dumb--guaranteed to boil off the main caps in
short order.

The $13 unit has a rugged-looking BJT 1/2 bridge, twice the rating,
smaller magnetics, and is acceptably not-as-quiet. I hesitated at
getting a cheapo, but, inspecting, it really looked surprisingly
well-made. The big caps are sagely remote from heat sources.

Installing the new supply, I noticed a huge grill-shaped fan cutout
in the PC's back panel beneath the power supply, a bypass path ensuring
_no_ airflow to the peripherals. Gee, maybe that's why the harddrive
failed too. Compaq POS.

James Arthur

.

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