Switching MOSFETs are discharching?

Discussion in 'General Electronics Chat' started by Peytonator, Sep 18, 2014.

  1. Peytonator

    Thread Starter Active Member

    Jun 30, 2008
    105
    3
    Hello,

    I am trying to build a simple MOSFET driver that converts a 5V pulse to a 12V pulse. To do this, I used an N-channel (2N7000) and P-channel MOSFET (BSS84), as shown in Fig 1.

    If the input signal is a 5V pulse train, I notice that the falling edge of the output pulses decay instead of dropping immediately to GND. Fig 2 shows the signal at point A, and Fig 3 at Vout.

    I suspect this has to do with the output capacitance of the P-channel MOSFET creating a low pass filter with the 100k resistor. However, if I change the resistor to 10k, it doesn't seem to affect the output that much. I also tried changing the P-channel MOSFET but the signal shape remained the same.

    Could you please advise me how to correct this issue?

    Many thanks

    -----

    Fig 1 (circuit):
    Simulation1.jpg
    Fig A (point A):
    FigA.jpg
    Fig B (Vout):
    FigB.jpg .
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,649
    2,348
    Hello,

    Is there a load in your circuit?
    As shown the output looks open.
    Try an 1K resistor on the output and measure again.

    Bertus
     
    Peytonator likes this.
  3. Peytonator

    Thread Starter Active Member

    Jun 30, 2008
    105
    3
    Thanks Bertus - problem solved. Took longer to ask the question here than it did to solve it haha!
     
  4. wayneh

    Expert

    Sep 9, 2010
    12,156
    3,063
    What does your pulse train look like? And what is its source-sink current capacity?

    [never mind, looks like you got it solved]
     
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