From: wbrown@bevsun.bev.lbl.gov (Bill Brown)
Newsgroups: sci.electronics
Subject: Re: A much better power inverter design
Date: 11 Sep 1992 15:08:36 GMT
Organization: Lawrence Berkeley Laboratory, California
NNTP-Posting-Host: 131.243.192.17

In article <BuE4p8.5Bq@acsu.buffalo.edu> v064mb9k@ubvmsb.cc.buffalo.edu (NEIL GANDLER) writes:
>
>   I am a sophomore engineering student and have been researching and
>trying to develop a new type of car amplifier that runs cooler and
>the taim was at the power supply. 12v simply is not enough voltage
>to power speakers to large amounts of power unless multiple amps
>and speakers are used. So most manufactuers use mosfet power supplies
>that step up the 12vdc to higher levels by first providing a 60hz
>oscillating signal and using power mosefets to switch the 12v power
>to a step up power transformer which results in a larger square wave ac
>voltage output. This is rectified and the result is a dual polarity
>high voltage dc power supply for power amplifiers. But the mosfets although
>amazing devices have internal resistances that cause them to heat up a lot
>under heavy current loads. So I tried a mechanical method using 2 high
>speed quality relays. The design amazingly worked with little problems,
>like noise from the 60-hz modulated relays, a small amount of magnetic
>intereference which can be solved and slightly warm relays. The only
>major problem I can see is reliabilty. How many cycles can a relay take
>before they burn out, thats the only question. I must do more work and
>improve on this. Another small problem is irregularity, relays are not
>perfect bounceless switches and spikes and irregularities on the scope
>show up frequently on the square wave ac output. I have yet to try
>this with a power amplifier. [...]

Once again, we've gone 'round the full circle.

Back in olden days, when dinosaurs roamed the earth, yea, even before
the transistor came to be, all electronics were filled with strange
devices called "Valves" or "Vacuum Tubes".  In order for these strange
and wonderful devices to do useful work, or even provide Smoke, Smoke
being the active ingredient of all things electrical, they had to be
presented with High Voltage.

In mobile or portable installations this High Voltage could be provided
by various means; in some cases special batteries (known as "B" batteries
for the High Voltage was also known as "B+") were used.  In other cases,
generally where larger ammounts of "B+" were required, things called
"Vibrators" or "Vibrapacks" were used.

You have provided a fairly good description of how some of them worked;
the more advanced versions used mechanical resonance to provide the "clock",
and rather than a standard transformer used a coil configuration not unlike
that used in modern "switching" supplies.

You have also listed many of the disadvantages of this technology; these
are the reasons why hardly anyone bothers any more.  As one who has replaced
more than a few vibrators in car radios, marine transceivers, etc. I can
respectfully suggest that this is a technology whose time has not only
come, but also has went.  But you are to be congratulated for at least
trying out your ideas.  That, in itself, is encouraging; but it does remind
me of a quote about history being repeated.


Somehow, it makes me feel very OLD and tired.

Disclaimer:  These opinions are my own and have	    |
    nothing to do with the official policy or the   |  -bill
    management of L.B.L, who probably couldn't      |   wlbrown@lbl.gov
    care less about employees who play with trains. |