High power switching circuit problem.

  1. Hello all. I am trying to use a mosfet as a high power switch. I have an arduino nano pin controlling the gate of the fet. I am using an NTE2374 mosfet. I am using a typical circuit:
    [​IMG]

    I also have the gate connected to the source (ground) so that when the gate is not HIGH, it isn't floating.

    I have been testing this circuit on two separate components; main component (the valve) and also on an LED (not sure if this is a good idea). I have found the following things to happen:
    • When the arduino pin output is LOW and the component is either a valve of LED, the
      component was off (as it should)
    • When the arduino pin output is HIGH the LED turns on.
    • When the arduino pin output is HIGH the valve does NOT turn on and the voltage reading on
      my dc power supply goes from 15V down to zero in a moment.
    I have been at this for a couple of days and I can't seem to figure out what the problem is. Can anyone help me out or direct me towards the correct path? Thank you.
     
    Last edited: Mar 1, 2014
  2. jcsd
  3. It sounds to me like the 'valve' as you call it which I assume is a solenoid valve draws more current than your power supply is able to source.
     
    Last edited: Mar 1, 2014
    1 person likes this.
  4. Baluncore

    Baluncore 2,510
    Science Advisor

    D1 could have failed by going short circuit.
    The valve could have failed by going short circuit.
    The wires to the valve and D1 may have been swapped, which forward biasses D1.
     
    1 person likes this.
  5. Yes, it is a solenoid valve. So, I tried increasing the current knob on my power supply and..... it worked, LOL. Thank you. I hooked it up to my battery and it worked directly. I learned something new today: A dc power supply, by default, doesn't source current.

    Thank you Averagesupernova and Baluncore for the quick replies.
     
  6. You maybe have the diode in backwards?
    It's wired incorrectly?
    The power supply is current limiting at too low a threshold?

    What happens if you short across the FET to turn on the thingy.

    The FET input capacitance is 1300pf so the turn on will be slow. During that switching time the FET dissipates a lot of power. But even if the FET blew, I don't see how that causes what you describe.

    EDIT: Problem solved while I was typing
     
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  7. :biggrin:
    You got it. Thanks anyway!
     
  8. AlephZero

    AlephZero 7,300
    Science Advisor
    Homework Helper

    I was wondering why the LED that you tested first didn't burn out with 12V applied to it. That would explain it :smile:

    (But I didn't want to spoil everybody's fun guessing the answer by looking at ALL the evidence, so I didn't post this earlier!)
     
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  9. Aahahaha, didn't even cross my mind. Lucky led.
     
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