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2.5MHz Switching

Discussion in 'Electronic Design' started by icegray, Apr 22, 2007.

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  1. icegray

    icegray Guest

    Hi everybody,
    I must drive a nebulizer transducer and I need 2.5MHz 24V (almost
    200-300mA). I can create 2.7MHz 5V by microcontroller but I can't
    drive the fet to 24V.
    I am trying use two fets, first one drives second and second one
    drives transducer. Second fet can't switch after 1MHz.
    Could you please recommend a circuit for 2.5MHz 24V (almost
    200-300mA)?
    Thanks
     
  2. john jardine

    john jardine Guest

    (Assuming "24v" is not RMS or pkpk but a pulse peak height of 24V and the
    300ma is a peak value at the 24V.)
    Sounds like the nebulizer thing is a capacitor of 5nF. But at 2.5megs you'd
    need double that 24V to give a poor triangular output. Best to drive it as a
    class B amp'.
     
  3. VMOS?
     
  4. Henry

    Henry Guest

    The ICL7667 as a bridge driver with VCC=12V can do that.

    regards -
    Henry

    --
    www.ehydra.dyndns.info




    | Hi everybody,
    | I must drive a nebulizer transducer and I need 2.5MHz 24V (almost
    | 200-300mA). I can create 2.7MHz 5V by microcontroller but I can't
    | drive the fet to 24V.
    | I am trying use two fets, first one drives second and second one
    | drives transducer. Second fet can't switch after 1MHz.
    | Could you please recommend a circuit for 2.5MHz 24V (almost
    | 200-300mA)?
    | Thanks
    |
     
  5. john jardine

    john jardine Guest

    ......But at 2.5megs [---->and 300ma drive, you'd need 48V/uS slew---->]
    ...... to give a poor triangular output. Best to drive it as a
    class B amp'.
     
  6. SuperM

    SuperM Guest


    Hey, John... where was that 50Watt device you posted a link to?
     
  7. Jamie

    Jamie Guest

    use the FETS in common S mode., you only need the max voltage
    on the gate to fully saturate it.
    So instead of source feeding the transducer, you will be sinking
    the common side via the common source Fet.
    you simply need a 24 volt supply to feed the + rail for the transducer.
     
  8. Tam/WB2TT

    Tam/WB2TT Guest

    If you can use a sine wave, the solution is trivial.

    Tam
     
  9. Tim Wescott

    Tim Wescott Guest

    You sound like a digital guy -- "... fet can't switch ...".

    This should be relatively easy to accomplish with the right parts, but
    you have to treat it like an analog circuit. At that frequency you
    should be able to do it more or less like a base band amplifier with the
    right parts.

    So:

    * Get a copy of the ARRL Handbook. It will induce you to treat
    your circuit like it's RF, with lots of resonant circuits --
    resist it, unless you can be very certain of the capacitances
    not changing much. Even so, the Handbook has lots of good basic
    analog circuit knowledge for you.

    * Before you do any more work on the bench, get a copy of Spice
    (I like LTSpice, but you'll have to come up with your own MOSFET
    and transducer models). Make sure you can simulate the circuit
    before you build it.

    * You need 7.2 watts out, unless your load is highly reactive.
    If you can count on 25mW out of your microprocessor pin that
    means you need almost 50dB of gain -- and 25mW out of a 5V pin
    works out to 10mA. If you assume 20dB of gain per stage of
    amplification that indicates that you need at least three stages.

    * There may be drivers out there that can do this. It's up to you
    to find them, and my quick check to answer the question "what the
    heck is a nebulizer" indicates that maybe you want this solution
    to be cheap cheap cheap. Commercial power drivers usually aren't
    cheap, so you get back to a discrete circuit pretty quickly.

    --

    Tim Wescott
    Wescott Design Services
    http://www.wescottdesign.com

    Posting from Google? See http://cfaj.freeshell.org/google/

    Do you need to implement control loops in software?
    "Applied Control Theory for Embedded Systems" gives you just what it says.
    See details at http://www.wescottdesign.com/actfes/actfes.html
     
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