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Yet another mosfet driver circuit help needed.

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by ItsMike, May 22, 2011.

  1. ItsMike

    ItsMike New Member

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    Hey everyone,

    I've came across this pwm-mosfet driver circuit and i've came up with a couple of questions:
    [​IMG]

    Why did the designer put a zener diode on the input ? the transistor is going to be in saturation anyways right ?

    Also, what is the point of the 47k pull down resistor at the base of the transistor ?

    And why did the designer used such a small collector resistor on the EL7212 ?

    I managed to simulate the circuit the circuit with just the 1k base resistor and a 10k collector resistor, but than again I used ISIS to simulate it which doesn't seem to be very accurate.

    Thanks in advance,
    Mike.
     
  2. moffy

    moffy Member

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    Appears bad design. The EL7212 are meant to be driven by a 0-5v signal which I assume the input (A) is. That means the input transistor etc are superfluous. The 10 ohm resistor makes sense as short circuit protection, but will limit the max drive current.
     
  3. ItsMike

    ItsMike New Member

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    So can I just drive the EL7212 directly from a PWM CMOS output (from a pic or something) ?
    And attach the EL7212 output to the mosfet's gate directly ?
     
  4. dave

    Dave New Member

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  5. ronv

    ronv Well-Known Member Most Helpful Member

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    Can't see your picture for some reason.
     
  6. ItsMike

    ItsMike New Member

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  7. ronv

    ronv Well-Known Member Most Helpful Member

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    The only reason I can see for the transistor is to invert the input. As far as the zener goes - If the input is also 12 volts it would give some noise immunity because the transistor wouldn't turn on until about 4 volts instead of .7 volts. If the polarity is right I would eliminate the transistor and drive it with a 5 volt PIC.
     

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