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plasma speaker

Discussion in 'General Electronics Discussion' started by klayus, Jan 25, 2013.

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  1. klayus

    klayus

    4
    0
    Jan 25, 2013
    hello everybody! i am new here, and need your help!
    so i am building a plasma speaker i got the schematics from http://www.hackerbotlabs.com/2009/02/plasma-speaker/

    i made a pcb: http://tinypic.com/view.php?pic=ncio2f&s=6
    it didnt make any sound, only sparks, and then it died! the mosfet blew.

    so i designed another one using irfp240 and irfp9240 so i'll get less current per fet:
    this is the schematic:
    http://tinypic.com/r/1zej9fp/6
    and the PCB:
    http://tinypic.com/r/206hmar/6

    do you guys think it will work? is there anything wrong with it???
    what ever you have to say about it is welcome!!!
    thank you in advance
    best regards
     
  2. Laplace

    Laplace

    1,252
    184
    Apr 4, 2010
    How hot did the heatsink get just before 'the MOSFET blew'? How large was the heatsink? Did you mount the IRF540 with thermal conducting paste?
     
  3. klayus

    klayus

    4
    0
    Jan 25, 2013
    I found out that the mos did not blew up, a trace on the pcb melted! Is my schematic ok? Will it work?
     
  4. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,270
    Nov 28, 2011
    Your schematic diagram doesn't show how the MOSFETs are connected or specify what they are. You should know that we can't tell you whether it will work based on an incomplete diagram.

    But I think you're trying to use a push-pull drive. This won't work for several reasons. The P-channel MOSFET needs an inverted gate drive compared to the N-channel MOSFET. Driving a flyback transformer from a push-pull output defeats the whole idea of "flyback" and you won't get any significant voltage from it. The gate drive signals from the TL494 are single-ended and not designed to drive MOSFET gates; without pulldown or pullup resistors, the MOSFET will be driven only weakly and may stay in its linear region a lot of the time.

    This last problem is also present in the "Plasmana" design you posted. It's probably the reason why the MOSFET overheated. The TL494 is not designed to drive a MOSFET directly. You might get something workable if you add a strong pulldown resistor from TL494 pin 9 to 0V. But the TL494 is just not suitable for driving MOSFETs directly.
     
  5. klayus

    klayus

    4
    0
    Jan 25, 2013
    So, should i use a mosfet driver after the tl494? Can you sugest one that will work for this, or does anybody know a good schematic for a plasma speaker? I have a bunch of irfp240, maybe i can use them! Thank you, best regards!
     
  6. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,270
    Nov 28, 2011
    Yes, you could use a MOSFET driver. The TL494 is not an ideal device to be using here but you can probably interface it to a driver IC.

    The Microchip MCP1407 looks like it would be suitable. Use one output from the TL494. Connect the transistor collector to the positive supply. Connect the emitter to the MCP1407 input, and a pulldown resistor to 0V. I suggest say 3K3 for the pulldown resistor. Connect the two OUT pins of the MCP1407 together and through a low-value resistor e.g. 10 ohms to the gate of the MOSFET. Connect the drain of the MOSFET through the transformer primary to the positive supply rail, as before. Use plenty of decoupling!

    http://www.digikey.com/product-detail/en/MCP1407-E/P/MCP1407-E/P-ND/1228640

    I've only done very basic checks to find any obvious problems with this, and I didn't find any. That doesn't mean that I guarantee it will work! Good luck.
     
  7. klayus

    klayus

    4
    0
    Jan 25, 2013
    Thanx a lot! I'll see where i can find this part try the schematic and I'll let you guys know!
     
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