Can I use a power amplifier for power stage of a pure sine wave inverter?
The OPA541 data sheet says it can operate on power supplies as high as 80 volts and produce a peak current of 10 amps.

Now, if these are translated to a sinewave, the RMS voltage would be 80/2.828 = 28.3 volts and the current would be 10A/2.828 = 3.53 amps.

This would lead to a power output of 100 watts.

As you require 120V AC at 3A (power = 360 watts) you are well off-the-mark with this device and I have given it the most favourable chances in my analysis such as assuming it is a rail-to-rail output device.

For instance, if you dug deeper into the data sheet you would read that the output voltage swing on a 5A load and +/-35 volt power supplies is about +/-30V and this ratio won't be any better at +/-40V rails so, I'd expect the maximum output voltage to be only 70Vp-p or about 25 volts, leading to a power output of only 87 watts.

You would do better buying one of these: -



They cost about £20 from Maplin (UK source) and are rated at 200 watts into 4 ohms with a frequency response from 3Hz to 200kHz.