AMPLIFIER

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.

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

" 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

"GS"

... Phil

"John Lee"

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

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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.

On Tue, 14 Dec 2010 08:29:15 -0800 (PST), John Lee wrote:

--- No.

Driving a transformer on a winding (primary?) with fewer turns than another (secondary?) can get you almost any voltage you want out of the secondary

Also, driving any series LC at resonance will cause the voltage at the LC junction to rise to very high values if the Q isn't too low:

Version 4 SHEET 1 1476 916 WIRE 400 -368 -256 -368 WIRE -128 -336 -400 -336 WIRE 32 -336 -128 -336 WIRE 208 -336 32 -336 WIRE 32 -288 32 -336 WIRE -400 -256 -400 -336 WIRE 208 -240 208 -336 WIRE 32 -160 32 -208 WIRE 160 -160 32 -160 WIRE -256 -144 -256 -368 WIRE 32 -128 32 -160 WIRE 32 -16 32 -64 WIRE 32 96 32 48 WIRE -128 160 -128 -336 WIRE -400 176 -400 -176 WIRE -400 176 -496 176 WIRE -160 176 -208 176 WIRE 32 192 32 160 WIRE 32 192 -96 192 WIRE 208 192 208 -144 WIRE 352 192 208 192 WIRE -256 208 -256 -64 WIRE -160 208 -256 208 WIRE 32 224 32 192 WIRE 32 320 32 288 WIRE 352 352 352 192 WIRE 32 416 32 384 WIRE 352 464 352 416 WIRE 400 464 400 -368 WIRE 400 464 352 464 WIRE 208 528 208 192 WIRE -400 544 -400 176 WIRE 32 544 32 480 WIRE 160 544 32 544 WIRE 352 544 352 464 WIRE 32 592 32 544 WIRE 352 672 352 624 WIRE -400 720 -400 624 WIRE -128 720 -128 224 WIRE -128 720 -400 720 WIRE 32 720 32 672 WIRE 32 720 -128 720 WIRE 208 720 208 624 WIRE 208 720 32 720 WIRE -496 800 -496 176 WIRE -208 800 -208 176 WIRE -208 800 -496 800 WIRE 352 800 352 752 WIRE 352 800 -208 800 WIRE -496 896 -496 800 FLAG -496 896 0 SYMBOL voltage -400 -272 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value 12 SYMBOL voltage -400 528 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V2 SYMATTR Value 12 SYMBOL res -240 -48 R180 WINDOW 0 36 76 Left 0 WINDOW 3 36 40 Left 0 SYMATTR InstName R3 SYMATTR Value 1e6 SYMBOL nmos 160 -240 R0 SYMATTR InstName M1 SYMATTR Value Si7868DP SYMBOL pmos 160 624 M180 SYMATTR InstName M2 SYMATTR Value FDR840P SYMBOL res 16 -304 R0 SYMATTR InstName R6 SYMATTR Value 1500 SYMBOL res 48 688 R180 WINDOW 0 36 76 Left 0 WINDOW 3 36 40 Left 0 SYMATTR InstName R8 SYMATTR Value 1500 SYMBOL diode 16 -128 R0 WINDOW 3 36 32 Left 0 SYMATTR Value 1N4148 SYMATTR InstName D3 SYMBOL diode 16 416 R0 WINDOW 3 41 30 Left 0 SYMATTR Value 1N4148 SYMATTR InstName D1 SYMBOL diode 16 96 R0 WINDOW 3 37 34 Left 0 SYMATTR Value 1N4148 SYMATTR InstName D2 SYMBOL diode 16 224 R0 WINDOW 3 41 32 Left 0 SYMATTR Value 1N4148 SYMATTR InstName D4 SYMBOL diode 16 -16 R0 WINDOW 3 41 31 Left 0 SYMATTR Value 1N4148 SYMATTR InstName D5 SYMBOL diode 16 320 R0 WINDOW 3 43 32 Left 0 SYMATTR Value 1N4148 SYMATTR InstName D6 SYMBOL ind2 336 528 R0 WINDOW 0 61 31 Left 0 WINDOW 3 39 65 Left 0 SYMATTR InstName L1 SYMATTR Value 1.59e-5 SYMATTR Type ind SYMBOL cap 336 352 R0 WINDOW 0 -39 5 Left 0 WINDOW 3 -84 59 Left 0 SYMATTR InstName C2 SYMATTR Value 1.59e-7 SYMBOL Opamps\\LT1499 -128 128 R0 SYMATTR InstName U1 SYMBOL res 336 656 R0 SYMATTR InstName R1 SYMATTR Value .5 TEXT -472 832 Left 0 !;ac oct 256 20 1e6 TEXT -472 864 Left 0 !.tran 5e-4 startup uic

--- JF