It would need to be a standard power transformer though as I at one point tried a toroidal power transformer on the 60 watt bogen amp and it didn't like it at all. That means I can use a transformer with a higher secondary voltage of maybe 20-25V with a 100 watt amp. In this case one of those subwoofer plate amps might be my best bet. So i did some calculations for a 100 watt amp. The load in this case is a record player and 8 track player both with an AC motor. I don't really need anything to keep the voltage stable as the design I originally did pretty much held the voltage stable to where it only varied slightly based on the load. The VFD then won't work for me given it has to be isolated from RF sensitive equipment. Last edited by ACORNVALVE on Jul 4:19 pm, edited 1 time in total. The output voltage can be varied (from about 20 to 100%) as well as the frequency, but possibly not as much range as you might require.Being a switching design they are highly efficient. The method would work just as well for single phase variable frequency supplies, but the max frequency might not suit your application.įor this Avionics instrument application at least, the 0.75kW rated VFD gave an excellent stable & safe result and it does not have a failure mode where its output voltage can jump up more than a few % due to the tight control. Then I considered the Motor VFD (as was suggested early in this thread), most can set the base frequency from very low to 400Hz, these produce a PWM output that is effectively integrated by the motor's inductance, but there was no published design for a supply that I required, so it was a trip down a little traveled road, but I started playing around with power filters and I found that this integrated beautifully into a sine wave with a power L-C filter:
And there were some size & efficiency issues to consider.
I had considered it should be operated with a feedback loop and with over-voltage detection protection in case the input signal went up in level or became erratic or noisy. And it had to be three phase, just to make things more complicated.įor this application the audio power amplifier was considered too, however there was one thing that concerned me, that was amplitude control. I had a similar requirement, but it was for a 400Hz supply for testing Avionics instruments and supply perhaps 100W.
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