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distortion in 1MHz power OP AMP

distortion in 1MHz power OP AMP

(OP)

hi all.
really struggling with an issue Im having with a power op amp.
We are getting a distortion in the output waveform, a copy of it is below
http://files.engineering.com/getfile.aspx?folder=3...


we are driving a capacitive load and thus, have impedance matched the output of the power op amp (PA119) to the transducer.
The series R and transformer correct the real while the inductor checks the reactive.
Impedance matching is not the issue.
A copy of the circuit is below
http://files.engineering.com/getfile.aspx?folder=8...

We get this distortion whether the transformer 2ndary is connected to anything or not.
We get distortion regardless of the CC value (capacitor type, variable capacitors, etc).
We get the issue on two entirely prototype systems with independent equipment on each.
We do not get the issue if we drive a completely resistive but equivalent load (15ohms)
We are even using low inductance power resistors (for 10ohm) which keep the reactive load low.


You guys must have experience with this?
I mean is just a low inductance load?
Ive contacted the people that make the chip and they didn't have anything to help.

the only way I was able to correct this alittle was by shunting the output with an somewhat opposite reactive load (The R37)
It pretty much clears up any distortion..
with that said, we burn 3/4 of the power going through these two resistors.
A way to stabilize it without this resistor would be desirable

Any if anyone is really good out there, a way to go from a 1.5ohm source impedance to 35ohm while limited to 3 amps without using resistor would be great too..


RE: distortion in 1MHz power OP AMP

It could be that there is a little residual DC offset of the sine wave signal you are sending into your transformer TX1 which when the opamp voltage slope changes (sign change on the dI/dT) requires more out of the opamp to reset the flux of the transformer core.

Normally when driving a transformer a DC blocking capacitor in series with the transformer is used to remove any residual DC.

RE: distortion in 1MHz power OP AMP

(OP)

hi ComcoKid.
this was actually a pretty good idea.
It wasn't the problem though.

Ive given up on this product in the mean time
thanks

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