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Discussion in 'General Electronics Discussion' started by TheLacasse, Jul 9, 2017.

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  1. TheLacasse

    TheLacasse

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    Jun 8, 2015
    Hi, I'm looking for an electronic component that behave like a P-Channel MOSFET except that unlike the P-Channel MOSFET I want a high level signal to turn it on instead of a low level signal. It can be controlled by voltage or current and it need to switch fast so not a relay.

    Thank you
    Excuse my English
     
  2. kellys_eye

    kellys_eye

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    Jun 25, 2010
    N-channel MOSFET
     
  3. TheLacasse

    TheLacasse

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    Jun 8, 2015
    The voltage of the source need to be higher than the voltage of the drain and the load need to be connected to the drain which is voltage like I said is lower than the source voltage.
     
  4. davenn

    davenn Moderator

    13,866
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    Sep 5, 2009

    it's time you described EXACTLY what you are trying to do ... with a schematic and full description
     
  5. kellys_eye

    kellys_eye

    4,275
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    Jun 25, 2010
    In which case buffer the drive signal to the PMOS via an inverter - BJT or FET.... even a logic gate.
     
  6. TheLacasse

    TheLacasse

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    0
    Jun 8, 2015
    555-oscillator.png
    There is the schematic. This is an oscillator using a inductor and a resistor. So when the switch (SW1) is not pressed the 555 is reseted the output is low so the MOSFET Q1 is conducting pulling high the gate of the MOSFET Q2 so it is not conducting. When the switch (SW1) is pressed the output of the 555 become high because TRIG (0V at the beginning) is < 1/2 CV which is 2/3 of VCC. So the output of the 555 being high the MOSFET Q1 is not conducting the pull down resistor pull down the gate of the MOSFET Q2 so it is conducting. Then the inductor (L1) is being charged and it impedance is decreasing so the voltage of THRS is increasing until THRS > CV. When THRS > CV the output of the 555 became low so the MOSFET Q1 is conducting pulling high the gate of the MOSFET Q2 so it is not conducting. Then the impedance of the inductor (L1) is increasing and the voltage of TRIG is decreasing until TRIG < 1/2 CV and then the cycle restart again. My question was: Is there a single electronic component that can replace both MOSFET?

    Thank you
     
  7. TheLacasse

    TheLacasse

    15
    0
    Jun 8, 2015
    The problem I have with this setup is that the second MOSFET Q2 won't switch fast enough because of the pull down resistor at the gate. The gate of the MOSFET have some capacitance and pulling the gate low using a pull down resistor take some time. I could use a smaller pull down resistor but I already tried it, it worked kind of good with a 100 ohm resistor but I'm wasting energy when the first MOSFET Q1 is conducting. I did some research and I found something called a thyristor I never used them would it work?

    Thank you
     
    Last edited by a moderator: Jul 10, 2017
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