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Registered Member #3925
Joined: Fri Jun 03 2011, 10:50AM
Location:
Posts: 121
hey,
how do i modulate the supply to the zvs driver, to use it as a plasma speaker? and im gonna use seperate supplies, so should i modulate the 12v oscillator input to the circuit, or the power input?
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
You'd modulate the power input. To modulate it you have to modulate the voltage, how you do this is up to you. It could be a simple transistor burning off half of the wattage as heat, or a PWM buck converter with something like 80-95% efficiency (depending on design). There are many ways to do it.
Registered Member #3925
Joined: Fri Jun 03 2011, 10:50AM
Location:
Posts: 121
Arcstarter wrote ...
You'd modulate the power input. To modulate it you have to modulate the voltage, how you do this is up to you. It could be a simple transistor burning off half of the wattage as heat, or a PWM buck converter with something like 80-95% efficiency (depending on design). There are many ways to do it.
Registered Member #3215
Joined: Sun Sept 19 2010, 08:42PM
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Posts: 780
you could use the input inductor to modulate input by making a transformer out of it and feed the primary with an audio amplifier (or do the same with the flyback primary, who knows)
Registered Member #1316
Joined: Thu Feb 14 2008, 03:35AM
Location: Cambridge, MA
Posts: 365
You can use the input inductor as part of a buck converter. You only need one added power mosfet and a power diode. Its a commonly used configuration in florescent backlight inverters. See figure 2 in this pdf for ideas
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
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This will not work well, the series inductor will act as a low pass filter cutting the treble. And if you try to interrupt the supply current too fast, a huge voltage spike appears. It would help to put a reverse diode across the input.
Registered Member #540
Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969
In the diagram, there is a reversed diode but still, it would cut the treble of the sound because it takes a while for it to start oscillating and also a bit of time to stop. I think for CCFL inverters, they don't modulate it with a high freq. It's probably only enough so that your persistence of vision has just made it smooth. Otherwise they might run into efficiency issues with switching it too fast.
Registered Member #1316
Joined: Thu Feb 14 2008, 03:35AM
Location: Cambridge, MA
Posts: 365
CCFL inverters switch the mosfet as part of a buck converter a bit below the royer oscilator opperating frequency (usually above human hearing). The circuit is a modified buck converter. Because the ZVS driver or royer oscilator are current fed, you can PWM its input choke directly to change the average current (buck converter). The buck converter stage and the royer oscillator share the same inductor. This eliminates the filter cap after the output of a conventional buck converter, and the input choke for the ZVS driver that would be required for a completely separate buck converter stage to be used.
I do not believe that the PDF I linked to has the driver circuitry for the buck converter shown in the referenced diagram. However, the design should be very similar to that of a conventional class D audio amp, and there is many circuits online to look at.
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implimenting voltage modulation of zvs driver for plasma speaker usage?
