IRFD9120 Test Circuit

Discussion in 'The Projects Forum' started by RodneyB, Jun 8, 2015.

  1. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
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    I have been given a single IRFD9120 to use to switch a 35mA load that is a small tracking unit. Before I build or try to build the circuit I want to test the P cannel Mosfet.

    As I only have 1 I want to make sure I have the right test circuit. From there I can build the final circuit. Could it be checked and I will be only to happy for any advice
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    I doubt 91K will light the LED.
    Try a 330 R one
     
  3. RodneyB

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    Apr 28, 2012
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    Sorry that was a stupid error on my behalf. :( is the rest of the circuit in order
     
  4. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    nope, you have the mosfet backwards. See that little diode drawn inside the mosfet? That really is present inside, and would conduct regardless of what is on the gate of the mosfet.
    Also the resistor and switch are wrong, the resistor should be connected between source and gate of the mosfet, and the swtich between ground and gate. Also the value of the resistor should be 10-100 times lower.
     
  5. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
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    This is a P-Chanel Mosfet?
     
  6. RodneyB

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    Apr 28, 2012
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    I have changed the drawing?
     
  7. kubeek

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    Sep 20, 2005
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    No you haven´t.
     
  8. RodneyB

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    Apr 28, 2012
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    Sorry uploaded the orginal
     
  9. kubeek

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    Sep 20, 2005
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    The mosfet is stil upside down. Otherwise it seems ok.
     
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  10. RodneyB

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    Apr 28, 2012
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    The symbol for the P-Chanel Mosfet I get from the symbol Library of Proteus 8 professional
     
  11. kubeek

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    Sep 20, 2005
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    Well that doesn´t really matter where you got it, but you need to connect source to +12V and drain towards the LED, not the other way around.
     
  12. RodneyB

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    Apr 28, 2012
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    I am totally confused now. I have changed the drawing is this right ? :(
     
  13. kubeek

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    Sep 20, 2005
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    no, leave the transistor where it was, but flip it upside down, so that source goes towards the supply voltage and drain towards the diode.
     
  14. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
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    Thank you, Its now making sense
     
  15. kubeek

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    Sep 20, 2005
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    Yes, now it is correct.
     
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