Mosfet driver Vs circuit

Discussion in 'The Projects Forum' started by 7Arrows, Feb 19, 2010.

  1. 7Arrows

    Thread Starter New Member

    Feb 14, 2010
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    Hi all
    The goal is to provide the fastest turn off possible and keep board noise as low as possible.
    Is there any advantage in using an IC like the MPC1406 over the circuit shown?
    7Arrows
     
  2. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Have you considered a "speed up" diode parallel to the gate resistor to drain the gate? Many of the application notes on gate drives mention it.

    John
     
  3. 7Arrows

    Thread Starter New Member

    Feb 14, 2010
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    Thanks for the reply found some good information on gate drives answered a lot of questions I had.
    Using a speed up diode you can soften up the turn on and keep a fast turn off this should help keep the power supply a little more stable.
    7Arrows
     
  4. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    The 2.5nF cap in your 1406 schematic will slow down turn-off time and increase noise.
    The reason you see it in the datasheet is that it is there to simulate a MOSFET gate capacitance during testing.
    What is the purpose of the diode in the drain circuit? It needs to be in parallel with the inductor, not in series. In series, it will not protect your MOSFET from the inductive flyback voltage spike which occurs when you turn off the MOSFET.
     
  5. 7Arrows

    Thread Starter New Member

    Feb 14, 2010
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    Thank you for finding my error with the cap.
    The diode D8 in the drain circuit keeps the capacitance in the Mosfet from draining into the coil when it’s turned off. Here’s an up dated schematic.
    7Arrows
     
  6. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    I don't see how that is possible.
    What is the other end of your coil connected to? What is the inductance? How are you going to protect the MOSFET from the flyback voltage?
     
  7. 7Arrows

    Thread Starter New Member

    Feb 14, 2010
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    The coil inductance is about 320uH fly back voltage should peek at about 400 volts the other end of the coil is hooked to a couple of clamping diodes then into the detector preamp. This circuit runs at 1000Hz and the coil is pulsed for 100us seconds.
     
  8. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    Ah, a pulse induction metal detector!
     
  9. 7Arrows

    Thread Starter New Member

    Feb 14, 2010
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    Yep it’s my Frankenstein project a little from here a little from there. Still need to come up with a ground balance circuit and decide on a power supply.
    Thank you for the help
    7Arrows
     
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