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Re: Monitor Problems

mdj wrote:

Michael J. Mahon wrote:



:-) This is a fantastic story! Makes my audio amplifier power supplies
seem tame (~90V secondaries with 40,000uF)


That's a lot of stored energy--162 Joules!  You could do some serious
spot welding with that!  And 90v is enough to shock humans (while
anything under 45v is not).



Well, it certainly eats screwdrivers :-) I learned through experience
that most of the time, the difference between an excellent amplifier
and an average one is the capacity of its power supply. In that case, I
happened upon a decent sized batch of high voltage 10,000uF electros,
and added caps until the supply rails were undisturbed while the amp
was under load.

You definitely need a bleeder jumper for discharging them - as you
point out the spot weld effect is sufficient to seriously damage the
terminals of the electros.

I've been continually appalled by the quality of power supplies in most
domestic grade audio equipment, but then considering what the above
mentioned supplies cost to build not to mention the weight of the
torioid transformers, I suppose it is a matter of paying for what you
get.



I have a bit of a wierd fascination with power supplies, which I guess
is kind of like the oily hand brigades fascination with cubic inches.
You mentioned a while back some experience with an ECL machine - while
fairly harmless, I'm sure the power supply for such system would be
really a sight to behold (at least those of us who are fascinated by
banks of capacitors) :-)


True.  A large ECL machine demands low voltage at very high current.
The prototype I mentioned had a couple of 500A power supplies at 3.7v
(or something like that).  They were high frequency switching supplies,
but since the current was so high the filter capacitors were also huge--
like 100,000uF (or .1F  ;-).  The power supplies were about 20% of the
volume of the machine.  I was really impressed by the bus bars that
delivered the power--about 1" x 3/8"!



That's just awesome! I suppose the supply designs could have been quite
simple too, since ECL circuits don't tend to produce a lot of
electrical noise, but gosh two 500A supplies, that's a tremendous
amount of quiescent current.


ECL had a reputation for being the "hottest of them all'.


One wonders when the 'wall' of CMOS switching speed will be reached and
we have to start exploring ECL designs again. Certainly that's been
said before, but there's something about the design that really appeals
to me.


Most of the power that CMAS dissipates is "AC power" associated with
switching (and the consequent charging/discharging of capacitance).
The quiescent power for CMOS is quite low--unless the process is
making very leaky transistors.

So the only way to dissipate less power at high frequency is to 1)
decrease resistance, 2) decrease capacitance, or (most popular) 3,
decrease voltage swing.

Efforts are proceeding on all fronts:  copper in place of aluminum to
reduce resistance, low dielectric insulating layers to reduce
capacitance, and lowering operating voltage.  Unfortunately, all three
are becoming more difficult, so maximum clock frequencies are not rising
like they used to, and Moore's "Law" isn't being enforced like it was.
;-)

-michael

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Home page:  http://members.aol.com/MJMahon/

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