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How would you build a 20W 400Hz 24V RMS sinewave generator?

Gyrocompass?

There are smaller chips, more in your power range, but that TPA3255 isn't expensive. Somebody makes a nice heat sink that parks on top; the power pad is on the top of the chip.

We make a couple of synchro i/o things,

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but they are low power, all linear amps. Our main power limit is the transformers.

The big one is 3-phase but currently fixed at 120 degrees, to simulate a jet engine permanent-magnet alternator that powers the engine control computer. Phase angle accuracy doesn't matter. Actually, no accuracy matters!

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Since it has an FPGA doing DDS into DACs, it could have programmable phases if anybody wanted it. I think all the phase registers are there already. The only tricky part was the programmable current limiting.

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John Larkin      Highland Technology, Inc 

The best designs are necessarily accidental.
Reply to
jlarkin
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So you want a well-defined and stable 400Hz waveform. That puts the Class-D oscillator out of court. Of course if you inject a 400Hz component in quadrature with the output into the tank circuit, you are effectively synthesising an additional reactive component in the tank circuit, and can trim the frequency and phase to be exactly what you want by adjusting the magnitude of the current you inject.

I've got LTSpice simulations of circuits that would do the job, but it's unlikely to lead to a particularly cheap or simple circuit.

Analog Devices have lots of Direct Digital Synthesis chips which could give you exactly the waveform you wanted. Boosting the output to create the amplitude you need would take more work, and regulating the amplitude to maintain a steady 24V rms would take a bit more still.

So you've got to make up the losses in your load as well as the losses in the transformer you are exciting. Not a big deal

Analog Devices do sell Direct Digital Synthesis chips which can generate more than one waveform - up to four if I remember rightly - with very closely specified phase relationships. They aren't all that cheap, but it is a single chip solution to that part of the problem.

24V rsm is +/-37.7V peak to peak.

Could be. Pulse Width Modulation always produce higher harmonics, which you'd probably have to filter out. You trade heat dissipating elements for filter components.

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Bill Sloman, Sydney
Reply to
Bill Sloman

It is intended for that sphere, yes.

The box I am developing will generate these outputs.

Getting a sinewave is no problem; I can feed a load of sin(x) values to a DAC, using DMA fed from a circular buffer.

Reply to
Peter

We used DDS in an FPGA to make our sine waves, feeding a serial quad DAC. Phase accumulator, phase shifter adder, sine lookup table, multiplier to scale the amplitude. One of my kids did the VHDL. The lookup table and I think some of the other logic is shared between the three phases; at our frequencies, we have time to spare.

Synchros are astounding. Some will run red-hot.

Some have arc-second accuracy. It's hard to build electronics that good.

--

John Larkin      Highland Technology, Inc 

The best designs are necessarily accidental.
Reply to
jlarkin

Or you buy it all in one purpose-built lump as a Direct Digital Synthesis chip from Analog Devices. Not cheap, but not much development time either.

Not so much hard as time-consuming and tedious.

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Bill Sloman, Sydney
Reply to
Bill Sloman

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