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I need a power supply with two 100W isolated AC outputs. The output voltage must be a 24V 10kHz sine wave. The load regulation is not so important, what is truly important is the preservation of the sinusoidal wave shape under both rated load and no load conditions. Which SMPS topology is best suited for this purpose?

The first thing that came to my mind is an AC/DC SMPS (PFC + isolated step-down) followed by a PWM inverter. But I think that it is over-complicated for such a seemingly simple task.

The second thought was to get rid of the inverter. Indeed, we already have a rectangular AC voltage after the step-down stage. Maybe we can filter it instead of rectifying? I also found information about resonant converters, and that they can be used as AC/AC converters.

So what do you think about it?

Some additions

  • The input is 230V 50Hz mains.
  • Load regulation: 20% is OK.
  • The same with THD: 10-20% is OK.
  • I'm sorry. I forgot probably the most important thing - efficiency! It should be at the level of an average SMPS, 80% or more.
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  • \$\begingroup\$ How do you get a "rectangular" ac voltage on the input side? How much distortion/harmonics can you tolerate in the output "sinusoidal wave shape"? You didn't tell us the frequency of the input but I assume that it is normal mains at 50/60 Hz...no linear filter will change that to 10 kHz. \$\endgroup\$ – Elliot Alderson Aug 11 '18 at 20:08
  • \$\begingroup\$ You want a 100W long-wave oscillator. Nothing else. Create that sine the analogue way, it's much simpler than any kind of D/A mumbo-jumbo. \$\endgroup\$ – Janka Aug 11 '18 at 20:31
  • \$\begingroup\$ @ElliotAlderson Yes, the input is 50Hz 230V mains. As for the rectangular voltage I meant the output of the step-down stage. The PFC stage rectifiers mains voltage and converts it to the 400V DC. The step-down stage chops the DC at high frequency and feeds the isolation transformer. At the output we have a low-voltage high-frequency rectangular wave. By filtering it you can get a required sinusoidal voltage. At least I hope so. \$\endgroup\$ – Dmitry Aug 11 '18 at 20:33
  • \$\begingroup\$ I go so far even recommend a motor-generator. \$\endgroup\$ – Janka Aug 11 '18 at 20:34
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    \$\begingroup\$ If load is 100W what is allowed voltage drop or load regulation error 2% 10%? 1%? Maybe you just need to buy a stereo audio power amp. You specs are too thin. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Aug 11 '18 at 20:43
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You say you want two 10 kHz 100 W outputs. You didn't say what the input to this power supply is, so I'll assume normal 50 or 60 Hz line voltage.

In that case, the input 50 or 60 Hz is really of no use directly. Use it to create DC, then use that to make the 10 KHz. You only need a single 200 W (plus a little for losses) output that drives a transformer with two secondaries.

The DC to AC converter could be something like a class D amplifier with a little resonance to be really good at your single output frequency. For simplicity, you could just get a 250 W audio amplifier and feed it a 10 kHz signal. That's more complex inside, but that doesn't matter if you're buying it as a pre-made off the shelf box.

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  • \$\begingroup\$ If I get you right, you suggest to control the chopper using PWM, then filter out the carrier to get the desired 10kHz sine wave, and lastly feed this signal to an isolation transformer? Yeap, I think it might work. \$\endgroup\$ – Dmitry Aug 12 '18 at 13:47
  • \$\begingroup\$ @dmit: If you are going to make this yourself, then chopping directly into the primary of a transformer would probably be the simplest. A center-tapped primary can simplify the drive circuit, depending on the DC voltage you start with. With fast enough PWM, you may not need any more deliberate filtering except caps across each of the secondaries. 20% THD isn't that hard and doesn't require a lot of fancy filtering. \$\endgroup\$ – Olin Lathrop Aug 12 '18 at 16:33
  • \$\begingroup\$ After some additional research I think that it is the most optimal way... \$\endgroup\$ – Dmitry Aug 13 '18 at 14:29
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How about a self oscillating resonant scheme set up at your required 10KHz .A simple circuit like a ZVS Royer or maybe a half bridge like on CFL lamps .You will get reasonable efficiency and low EMC .Remember that you need a 10 KHz transformer and some 10 KHz components to shape your desired sine wave .The switching devices are not highly stressed in these schemes so good reliability is to be expected if peak currents and peak voltages are limited.

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