mosfet not switching

Discussion in 'The Projects Forum' started by Yebon, Dec 17, 2013.

  1. Yebon

    Thread Starter New Member

    Dec 17, 2013
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    I have a project that is using a car battery for power and a 5 volt touch plate as the signal. When i connect to power and i turn it on ( touch the switch) it turns on but it does not turn off. I am not sure where to go from here. Is the resistor from gate to source the wrong value? (part numbers are listed on drawing and they are correct)

    any suggestions would be appreciated.
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The inputs to U3 left floating?
    Max.
     
  3. Yebon

    Thread Starter New Member

    Dec 17, 2013
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    should I add a resistor from the touch pad (signal) to the driver inputs (U3)?
     
  4. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    I would put a 3 to 10 MOhm resistor between touch pad and ground. The touch pad needs to discharge at some point. Play with the resistor value to make sure it the touch pad discharges enough to turn off the driver in a reasonable time (larger for longer times).

    On the other hand, if the resistor is too small of value, the current will flow (and voltage drop) so fast that the mosfet never turns on.
     
  5. Yebon

    Thread Starter New Member

    Dec 17, 2013
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    I have added the resistors that you suggested is this what you mean? I am sorry i may be way off base with your suggestion.
     
  6. #12

    Expert

    Nov 30, 2010
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    The data sheet says the inputs are held low when left floating. The drawings show 400k internally connected from the inputs to ground. These things say the output should not float.:confused:

    Maybe something else is wrong.

    ps, Yebon...you did what was requested.
     
    Last edited: Dec 17, 2013
  7. ronv

    AAC Fanatic!

    Nov 12, 2008
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    Maybe you can check the voltage level at the input and output voltage of the ucc27524?
     
  8. Yebon

    Thread Starter New Member

    Dec 17, 2013
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    I read the data sheet for the driver and it suggests 2 caps in parallel from VDD to GND. i have added this to the schematic. Does anyone else see anything that jumps out that i should add or take out. Thank you all for your help.
     
  9. ronv

    AAC Fanatic!

    Nov 12, 2008
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    :)Add the voltage measurements.:D
     
  10. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    Does the EVK1010A already come with an electrode or did you do this part yourself including the capacitor selection mentioned in the datasheet of the AT42QT1010?
     
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