Re: heat and more heat with heatsinks? what do you think?

On Sun, 15 Jul 2007 14:50:50 -0500, Frank McCoy <mccoyf@xxxxxxxxxxxx>
sayd the following:

In alt.comp.hardware.pc-homebuilt Crackles McFarly
<IrelandSux@xxxxxxxxxxx> wrote:

On Sat, 14 Jul 2007 16:10:37 -0700, "jameshanley39@xxxxxxxxxxx"
<jameshanley39@xxxxxxxxxxx> sayd the following:

a question i really want to ask you, is what type of school (high
school? university?) , and what subject, does one build that sort of
thing?
I don't know of any high school or university.. I'm interested,
because it'd a good background to have.

I was a higher level electrical engineering course for designing power
supplies. Not static voltages but ones that varied from near-zero to
13+ volts. The idea was to keep the voltage regulators from drifting
and making the voltage slowly drop.

Was tested on a large power resister to make the result come quicker.
The grade was based on the drifting and also how much time it took for
a drift to be seen.

No drifting was the goal but very few could do that for more than 10
minutes...The old heat got the best of most of us.

The worst was a drift of 5 volts in under 3 minutes while the best
went nearly an HOUR and even then only dropped less than a volt.

It was an interesting little experiment for me at least.

Hmmm ... Must have been pretty simple supplies, or with a set specific
diagram. Any power-supply that *I* ever designed that drifted more than
a tenth of a volt under no load or full load for several *days*, would
have been scrapped and redesigned.

Mostly I expected far better than that. I wanted my calibrated setting
to match my output if possible; and far more-so I didn't want the damned
thing *drifting* with changes of input-source, use, or output-load. If
I couldn't rely on my power-supply to remain stable, then how could I
trust my circuit to continue working?

(Of course, a complementary task was to make a circuit WORK with a wide
range of input volages; allowing the use of cheaper power-supply
circuits. But to test *that*, called for a reliable test-bench supply.)

It wasn't until I was pretty much out of the business of designing audio
circuits that I finally managed to afford a GREAT HP power-supply with
even better specs than those I designed myself. Great, huh? You
finally get decent equipment when you no longer need it. However, I
still have one of the supplies on my bench that I built myself. For a
*tiny* supply, I haven't yet found anything to match it in
specifications or ease-of-use. Both voltage and current-regulated in a
tiny 3" by 4" box. I tore out the guts of a truly *cheap* commercial
supply I got that was pretty worthless, kept the knobs and case, and
replaced pretty much everything else. A bit of a chore making that
tight a control of the output without the tight feedback circuit wanting
to oscillate; but it does work wonderfully. "Hard as a brick."

One of the tricks of the device was to make the pre-regulation of the
voltage-standard inside independant of the circuit it was regulating;
yet using the same standard. (If the voltage to the standard varies
under line or load ...)

I've seen that happen on all too many otherwise good supplies. Under
full rated load, the supply to the reference dropped, which dropped the
output, even though the supply itself could have otherwise handled the
extra current.


If only I had designed mine with a superconductor..
;-)

.

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