Opamp based power amplifier

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Can anyone plz give me the design of a high power opamp based amplifier, Vcc(100-200V, single power supply), Output current(tens of amperes)
 

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  • #2
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Do you know a lot of power amp are op-amp based. If you look carefully, a lot of them have negative feedback from the output to the inverted input!!! It might not be that obvious but it's there.....from old school Fender and Marshall tube guitar amps to Hi Fi amps, they all are op-amp based design with a differential tube that has +ve and -ve input and feedback from the output transformer.

Why do you want to have that high a voltage? You are going to limit your transistor selection. Also you are going to have to be more specific on how many watts, what class, what is the frequency requirement etc.

I think you'll have better choice if it is +/-40V or so supply.

OK, I just pull this one out from my behind just for the fun of it!!! It's Saturday and I have nothing better to do so I just whipped it up, don't take it too serious!!!

24liss4.jpg


You can parallel as many output transistors as needed. This is a standard inverting op-amp design. I feel it's easier to compansate in the inverted configuration. This is only a starting point, dominant pole is needed and a lead lag network might be needed depend on what load it is driving. The one resistor adjustment is to adjust how class AB you want, all the way to class A. Output should be sitting at +50V. The input differential pair need to be matching pair ( dual transistor) if precision DC is needed.
 
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The OPA541 may be about as close as you're going to get. It has the drive current but not the voltage you want.

http://focus.ti.com/lit/ds/symlink/opa541.pdf

It's not quite correct to say that the output stage of a Fender or Marshall tube amp is an op-amp. It is not. An op-amp is a DC coupled amplifier with immense gain. The output stage of the typical push-pull tube guitar amplifier is never DC coupled and has a voltage gain between input and output of perhaps 10 or 20. It has a very high power gain begin able to take a 2 volt signal at it's input and turn it into a 20 volt signal into an 8 ohm load.
 
  • #4
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The OPA541 may be about as close as you're going to get. It has the drive current but not the voltage you want.

http://focus.ti.com/lit/ds/symlink/opa541.pdf

It's not quite correct to say that the output stage of a Fender or Marshall tube amp is an op-amp. It is not. An op-amp is a DC coupled amplifier with immense gain. The output stage of the typical push-pull tube guitar amplifier is never DC coupled and has a voltage gain between input and output of perhaps 10 or 20. It has a very high power gain begin able to take a 2 volt signal at it's input and turn it into a 20 volt signal into an 8 ohm load.

Op-amp is defined with high open loop gain with +ve and - input. Yes, really straight speaking , those tube amps are not because of that, but it has all the characteristic of an op-amp.

What I drawn is a typical power amp in op-amp config. What he is asking is very high power amplifier. Check Apex, I used a lot of their HV op-amp before, but I doubt you can find one to do the job, it got to be a few in parallel and is very very expensive.
 

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