Hi,

I need to create an amplifier, capable of producing up to 100V, with input signal of cca 3V.

My idea was to use an opamp and transistor output stage, but I don´t know how to do the feedback so that the response is linear.

Any suggestions?

 

Hello,

A 100 Volt amplifier is mostly made with a power amplfier driving a tranformer.
This used to be done in the past for audio distribution.
In the homes there was a transformer to bring it back to a lower voltage for the speaker.

Greetings,
Bertus

 

What kind of load will it feed? What kind of current will it have to supply?

 

Sorry for the inaccuracy, I didn´t mean a PA distribution amp.
It is supposed to be DC coupled, and should be able to make a 100V ramp in about 1ms.

The load should probably not be too big, I guess in the range of 10kohm and more. I don´t have any specifics on the load yet as I am just trying to help my friend, but let´s take this as a starting point.

I don´t need the circuit solved with included exact part numbers, what I need is more of a general topology to achieve this.

 

Hello,

Here is a link to the leach superamp.
It is a 270 Watt power amplifier.
http://users.ece.gatech.edu/~mleach/superamp/
It is supplied with ± 85 Volts.
Perhaps you can get some ideas for the higher voltage setup.

Greetings,
Bertus

 

It is supposed to be DC coupled, and should be able to make a 100V ramp in about 1ms.

It's starting to sound like you only need to source current, not sink it. If so, you would not need a push-pull output stage. Do you have any limitations on power supplies and grounding. For example, can you have dual power supplies for the OPAMP +/- 15VDC, with 100VDC for the transistor supply and the load connected to ground?

Are these allowable starting assumptions?

 

Looks like National may have the solution - just make an integrator. http://www.highvoltageinfo.com/2008/01/high-voltage-op-amp.html

 

Thanks for replies to all. I still don´t have any details, but lets "suppose"

bertus and steveb: I guess the push-pull would be better just to be sure, I was thinking of opapmp on the input, then VAS (voltage amplification stage) and then some classical push-pull follower, and general feedback from the output to the opamp.

Another possibility is a long-tailed pair on the input instead of the opamp, which could make the design a bit easier.
The thing I need help with is the VAS, because right now I have no idea, mostly what the gate, drain and source resistors should be.

Now this starts to look like a general scheme of opamp/amplifier with feedback, so do you have some materials on that?

beenthere: thanks for the link, but the parts seem to be quite hard to get. The ramp signal is coming from a function generator, so I don´t need the integrator.

 

Sorry for the inaccuracy, I didn´t mean a PA distribution amp.
It is supposed to be DC coupled, and should be able to make a 100V ramp in about 1ms.

The load should probably not be too big, I guess in the range of 10kohm and more. I don´t have any specifics on the load yet as I am just trying to help my friend, but let´s take this as a starting point.

I don´t need the circuit solved with included exact part numbers, what I need is more of a general topology to achieve this.

I'd try a true complementary amplfier with a couple of good high voltage transistors. Use no feedback, so as to keep the slew rate high. Drive it with a simple class A transistor, and voila!

eric