mosfet behavior abnormal in yenka

Discussion in 'General Electronics Chat' started by Yuright, Apr 4, 2011.

  1. Yuright

    Thread Starter New Member

    Apr 3, 2011
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    I have been playing around with electronics for about a year and have utilized the Yenka simulator often. I have been working on a control circuit which is switching a 24 volt power source. On the bread board everything works fine but if I build the circuit in Yenka it will crash the mosfet in the simulation. It shows the gate receiving main power supply voltage when the Vgs is only 10v. What is odd is that the component fails even when I just connect a wire to nowhere. The only way I have made it work is to connect my gate control voltage while the component is in the failed mode then restore it. However if I try and switch the gate on and off it will fail again. Is there something I am missing about the operation of a mosfet or does yenka's sim have a bug? Thanks
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Since you haven't posted a schematic, we don't see what you're seeing.

    It's possible that you are trying to use a depletion mode FET rather than an enhanced MOSFET, but really - we need to see the schematic.

    Do a screen print, paste into MS Paint, save as a .PNG, and then upload to here using the "Go Advanced" and "Manage Attachment" buttons to upload it from your computer.
     
  3. Yuright

    Thread Starter New Member

    Apr 3, 2011
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    0
    Here you go. The mosfet is an IRF520 enhancement mode. 20v max Vgs. I have run this circuit on a breadboard using several different mosfets and up to 35v with no problem. But in yenka it blows up as soon as you connect anything to the gate.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Yes, it looks like Yenka's broken.

    I don't see any path where the gate could even get to 12v.

    You have two 10k resistors in series across 24v, and you've connected a switch to the junction of the two resistors.

    When the switch is closed, the pull-down resistor on the gate winds up being in parallel with the left-side 10k resistor; so you have 10k on the top of the divider, and 5k on the bottom. Your Vgs would then be 8v.
     
  5. Yuright

    Thread Starter New Member

    Apr 3, 2011
    14
    0
    Thanks for taking the time to look at this. I feel better now.
     
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