AMPLIFIER

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

Reply to
John Lee
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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.

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Tim Wescott
Wescott Design Services
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Reply to
Tim Wescott

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.

Reply to
Bitrex

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

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Reply to
Vladimir Vassilevsky

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

Reply to
GS

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.

Reply to
George Herold

That's simple: put an RC on top of the other RC.

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant

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Reply to
Vladimir Vassilevsky

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

Reply to
Tabby

Nah. All you need is a transformer.

Hope This Helps! Rich

Reply to
Rich Grise

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

Reply to
Joel Koltner

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      |
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Reply to
Jim Thompson

"GS"

** That practice began in the mid 60s with Ge power transistors like the 2N301.

... Phil

Reply to
Phil Allison

"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

Reply to
Phil Allison

You are correct. The key is that the driving amplifier has a low enough output impedance to support the step up in voltage.

Reply to
brent

And if you allow diodes, you can drive PMTs!

Cheers

Phil Hobbs

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Dr Philip C D Hobbs
Principal
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Reply to
Phil Hobbs

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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.

Reply to
George Herold

--
No.

Driving a transformer on a winding (primary?) with fewer turns than
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Reply to
John Fields

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