I am designing a power supply with output of 120Vac @ 400hz. I plan to use a full bridge mosfet output switching at 400hz. This will be a large square wave. I am thinking of using a pi filter to get a sinewave. Does this sound like a good idea?
Thanks in Advance... Paul
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No...
A T-type filter might work. If you must have a solid sinewave, the best way would be PWM, with faster transistors and control circuits if necessary.
Tim
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What is your power in watts requirement? Bad idea to filter it, generate the sinewave, send it to a Pulsewidth modulator, then apply it to a class D H bridge amplifier and then filter the output.
What is your power in watts requirement? Bad idea to filter it, generate the sinewave, send it to a Pulsewidth modulator, then apply it to a class D H bridge amplifier and then filter the output.
Power output requirement has not been determined. Could be as high as
2000W. Why is filtering it a bad idea? I have not designed a PWM before, please explain a bit more if you would. Are not H-Bridges driven by a control IC and the inputs to which are driven by square wave? Am I incorrect here? Can one feed the driver IC with a sine wave?Thanks
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Does
If you work through the math for a 400Hz filter, and consider the part-value implications, you'll find it's rather painful because of its size, cost and power loss. OTOH, if you make a sine-wave PWM chopper at say 40kHz, which is a 100x higher frequency, your filter component values will be reasonable.
A 2kW PWM system is not a trivial matter. I recommend you learn the engineering and practical principles by making a 50-watt PWM generator first. Then you can make a 250W model, and if you're feeling confidant, progress on to kW territory.
I think i know how to proceed. Two oscillators, one triangle @ 40KHz the other sine @ 400 Hz. Feed a comparator with both signals. The output of which will be PWM. This will feed the appropriate delay logic and then to the bridge driver and onto the MOSFETs. Since the output I desire will be
120Vrms @ 400hz. I will use rectified line (170Vdc) as the rail for the MOSFETs. Then filter the load with LC filter to get the fundemental freq of 400Hz. Does this sound plausible? Theoretically the output current would be limited to the capacity of the MOSFETs?Thanks
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