I'm trying to make this sine wave oscillator, but I want the amplitude of the voltage sine wave to be 4.8V and the output current amplitude to be 45A. I am not sure how to go about calculating for the amplitude for either the current or the voltage. Has anyone had some experience with these?
Best Answer
You are really asking two quite separate questions: 1) how do I make a 4.8 volt phase-shift oscillator (and I notice that you do not specify pk-pk, rms, or mean amplitude), and 2) how do I drive a 0.1 ohm load at this voltage?
1) The simplest way to regulate the amplitude is to make Rf slightly greater than necessary, and let the op amp saturation limit the amplitude by clipping. For this sort of circuit, having the gain slightly too high will not cause the output to develop into a square wave. Instead, it will stabilize with slightly flattened peaks. The actual amplitude will depend on power supply voltages and op amp saturation characteristics, so you'll need to do some research on that. You would follow such an amplifier with a voltage divider to give about 1 volt, which is a standard voltage level for the next stage, which is
2) Making high-current output will be a challenge. Assuming your voltage is rms, your output power will be (4.8 x 45) or a bit more than 200 watts. Your best bet might be to build a high-power audio amplifier capable of, say 300 watts, then feed a step-down transformer to lower the voltage. Assuming a nominal 8-ohm load for the amplifier, the output voltage is about 42 volts rms, so you'd need about an 8.6:1 ratio. If your signal frequency is around 60 Hz, you could use a standard power transformer designed to take 120 VAC and give 14 volts, which is a standard process control voltage. The transformer, of course, would have to be rated for more than your nominal 216 watts. If you're using a different frequency, you'd need to either design and build your own transformer, or find a source of specialty units. It's entirely possible that the audio amplifier connoisseur community might be a source of such a transformer.
On the other hand, if your frequency isn't too high, you might have a go at making an amplifier using an op amp followed by some high-current MOSFETs, although that discipline has some gotchas which you would need to learn about.