Please! Help needed with diode and mosfet selection.

Discussion in 'The Projects Forum' started by 1213brett, Feb 1, 2015.

  1. 1213brett

    Thread Starter New Member

    Feb 1, 2015
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    I am trying to not only build but understand how this project works. Its a sentry gun. I am new to electronics and when I built it my diode burnt up! I used a 1n4004 diode. And a 6v airsoft gun at least one that takes 4 AA's battery's. At first the gun made a noise and did not fire. I think it's not getting enough current. I went into the program and put the gun on full auto and it still just made a noise but a continuous one. Then I substituted the 4 AA's for a 6V 3700 mAh battery. The gun still did not fire then the diode burnt up . This was probably a dumb thing to do but I'm new to this sort of thing. even before I switched battery's It smelt like something may be burning. Obvasly I'm not shore but I think the mosfet is wrong too because like I said the gun did not fire it just made a noise for a second. I have the lights, switches and servos all working. Its just the gun firing that's giving me troubles. Thank you for any help. Hear is the schematic. Schematic_ArduinoBare.png
     
  2. #12

    Expert

    Nov 30, 2010
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    1) There is no power supply to U1
    2) That mosfet needs 6 volts to turn on well.

    You need a, "logic level" mosfet and enough volts to turn it on.
     
  3. Evil Lurker

    Member

    Aug 25, 2011
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    Second the motion on the logic level mosfet. I'd select one with a lower RDSOn, lower reverse blocking voltage, and higher amperage. And I would ditch R2 in favor of a gate current limiting resistor as Arduino pins can actively source and sink current... the deal is without a resistor you risk smoking your microcontroller's drive pin from over current when switching on/off a FET' thanks to their gate charge capacitance, or at least that is the way I understand it. Might want to go with a 1.5 to 3 amp diode in either fast or ultrafast recovery versions.
     
  4. 1213brett

    Thread Starter New Member

    Feb 1, 2015
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    Please be specific with components would the fqn1n50c that #12 suggested work for the mosfet?
     
  5. #12

    Expert

    Nov 30, 2010
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    #12 did not suggest the mosfet you already have. He merely provided the datasheet so others could know what you're working with.

    If you said how much current the motor uses, we could make a guess about a replacement part.

    Perhaps one of these:

    http://www.mouser.com/Semiconductor...w7404Z1yw729iZ1yw6zntZ1z0y3zrZ1yw8qn6Z1yw8pjm
     
    Last edited: Feb 2, 2015
  6. 1213brett

    Thread Starter New Member

    Feb 1, 2015
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  7. #12

    Expert

    Nov 30, 2010
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  8. 1213brett

    Thread Starter New Member

    Feb 1, 2015
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    If I change q1 to Mouser part 844-IRL530PBF and d2 to 583-RL852-B do I need to change r2? If so could you please help me choose a new one?
     
  9. #12

    Expert

    Nov 30, 2010
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    Change R2 to not existing and add a resistor in series with the gate to avoid burning the processor. See post #3
     
  10. 1213brett

    Thread Starter New Member

    Feb 1, 2015
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    How large a resistor should I put in series with the gate?
     
  11. #12

    Expert

    Nov 30, 2010
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    I don't know. I don't do Arduinos. Look on the spec sheet and find out how much current it can supply then put a limiting resistor in based on Ohm's Law.
    I=E/R
    Current available = voltage supply divided by the resistance you install.
     
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