Good day:
there are various amplifiers, but only RF power amplifier can output voltage higher than power supply rail? Is this correct?
other circuits like boost converter, voltage doubler, etc are not included in this discussion.
Thanks, John
Good day:
there are various amplifiers, but only RF power amplifier can output voltage higher than power supply rail? Is this correct?
other circuits like boost converter, voltage doubler, etc are not included in this discussion.
Thanks, John
It's not really a frequency range question, it's an amplifier topology question.
Any AC power amplifier that uses an inductor as a load can output voltage higher than the power supply rail. Of course, coil-loaded audio-frequency power amplifiers went out of fashion as soon as, or shortly after, transistors replaced tubes.
One could conceive of amplifier circuits that would do what you're asking for, but I doubt there'd be tremendous advantages to them.
-- Tim Wescott Wescott Design Services
In the case of an amplifying device with one terminal connected to ground, only an inductive load or LC tank circuit from the other terminal to the supply will allow the output to swing higher than the input, if the output is defined as being taken from the terminal of the active device not connected to ground. The frequency of operation, or what amount of power is being output is irrelevant.
Similarly, if the active device is connected with one terminal to the power supply, an inductive load on the other terminal will allow the output to swing below ground.
In its simplest form, though, a boost converter is nothing more than an amplifier with an inductor connected to the power supply, with its output allowed to swing above the power supply voltage.
This is not correct.
A passive circuit consisting of only Rs and Cs can provide voltage gain higher then 1. Hence over-the-rail amplifier can be built.
Vladimir Vassilevsky DSP and Mixed Signal Design Consultant
Car audio in the late 70's STARTED using inductive loaded transistor amplifiers. They were the first cheap high power amps, that could do more than the 12 volt car battery.
greg
r
" A passive circuit consisting of only Rs and Cs can provide voltage gain higher then 1. "
That sounds like a good trick (with no inductors). Vladimir, can your show me how it's done? I'm having trouble, unless you allow a switch.
George H.
That's simple: put an RC on top of the other RC.
Vladimir Vassilevsky DSP and Mixed Signal Design Consultant
Yes, requiring a switch of some sort. If you wanted to be really pedantic it can be done without a switch, just charge a cap and pull its plates apart.
NT
Nah. All you need is a transformer.
Hope This Helps! Rich
Vatche Vorperian's book, "Fast analytical techniques for electrical and electronic circuits" devotes some 10 pages to this ("RC filters with gain") -- although it's mainly to demonstrate a theory than anything where you'll come out with profound new insights as to the workings of the universe and start designing all your circuits in a fundamentally different manner than you do now. :-)
I can scan this in if you'd like...
---Joel
Why don't you do that, Joel?
I vaguely remember, so I'd like to see it formally again. ...Jim Thompson
-- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et |
"GS"
** That practice began in the mid 60s with Ge power transistors like the 2N301.... Phil
"John Lee"
** No.Any amplifier that incorporates and output transformer can do this.
Eg:
Most line voltage public address amplifiers operate from a single +24 volt DC rail yet output up to 100 volts rms of audio.
.... Phil
You are correct. The key is that the driving amplifier has a low enough output impedance to support the step up in voltage.
And if you allow diodes, you can drive PMTs!
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal
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OK, I'd like a copy too, since Jim's already 'ordered ya up'. Is that a good book?
George H.
-- No. Driving a transformer on a winding (primary?) with fewer turns than
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