Re: amplifier question

On Mon, 12 May 2008 13:30:56 -0400, "Arny Krueger" <arnyk@xxxxxxxxxx>
wrote:

I question your analysis. There will be times during an output cycle where
the load will be dumping current back into the amplifier. The amplifier
either absorbs this current, or the output voltage of the amplifier will be
greater than the output voltage which corresponds to the input signal. If
the amplifier provides a low source impdance, the voltage across the load
will be 99.9%+ as determined by the input signal.

It seems possible that virtually all of the current that the load dumps will
be absorbed by the amplifier.

If the amplifier's output devices are only partially conducting, then much
of the power that the load is dumping will be dissipated in the output
devices. That is why SOA was such a big issue for traditional Class A-C
power amplifier designs.

If the amplifier is a switchmode amplifier then the output devices will be
conducting very heavily, and very little power will be dissipated in the
output devices.

What bugs me is the issue of common-mode current. Apparently
the output inductors are a much bigger part of the design than
is obvious in an otherwise interesting description.

Maybe the reflected power is a related issue. Wish I were
smart enough to say how.


If this amplifier is somehow "recapturing" that energy,
what on earth is it doing with it, how is it recapturing
it and where is it putting it?

As always, the law of conservation of energy will assert itself, so the
excess energy stored in the load will have to go *some place*. Thus, it will
be absorbed by any lossy components of the load, any amplifier output
filtering network, the amplifier output devices, and the amplifier's power
supply.

In a low-loss system, most of the energy will end up back in the amplifier's
power supply.

Well, yeah, a linear amplifier must dissipate reflected power.
Is that all they were saying?


Much thanks, as always,

Chris Hornbeck
"I have a gift for enraging people, but if I ever bore you,
it'll be with a knife." -Louise Brooks
.

Relevant Pages

  • Rebuttal to Richard Clarks comments on my Chapter 19A
    ... RF power window at the input of the pi-network, ... plate, and the slope of the load line. ... the amplifier in this condition will later be shown to be 50 ohms. ...
    (rec.radio.amateur.antenna)
  • Re: Chapter 19A from "Reflections III" - Step 13 response
    ... It is thus evident that the amplifier has returned to delivering the ... was delivering 100 watts into the 50-ohm non-reactive load. ... reflected power, 30.6 watts, remains in the coax, adding to the 100 ...
    (rec.radio.amateur.antenna)
  • Re: Matching source and input impedances in power amplifiers
    ... RF equipment is designed to accommodate this matched condition, ... amplifier output connected to a transmission line, ... The load produces the ... As for power delivered to the *load*, more power will be delivered IFF the ...
    (sci.electronics.design)
  • Chapter 19A from "Reflections III" - Step 13 response
    ... It is thus evident that the amplifier has returned to delivering the ... was delivering 100 watts into the 50-ohm non-reactive load. ... reflected power, 30.6 watts, remains in the coax, adding to the 100 ...
    (rec.radio.amateur.antenna)
  • Re: amplifier question
    ... output cycle where the load will be dumping current back ... The amplifier either absorbs this ... dumping will be dissipated in the output devices. ... A-C power amplifier designs. ...
    (rec.audio.pro)