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Where can i buy the mosfets i need for my project?

Discussion in 'General Electronics Discussion' started by Cameron, Jan 25, 2018.

  1. Cameron

    Cameron

    1
    0
    Jan 25, 2018
    Hi! I am looking for cheap mosfets for a robotics project im making in school. It is controlled by a wireless xbox controller and a raspberry pi. I got all the coding out of the way, and i can send outputs from the pi, and i was using 3904 and 3906 transistors at first, but the motor im using spun really slow (i checked before assembling the circuit, the battery is enough for the motor). after some research, i found that i need mosfet transistors to make my project work. after confirming it with a circuit simulator, I looked on the internet for cheap mosfets, but couldnt find any, and honestly i dont even know what kind i need. any help is greatly appreciated. (edit- i need about 20 n channel mosfets and 20 p chanel mosfets)
    Screenshot (27).png Screenshot (28).png Screenshot (29).png
     
  2. Bluejets

    Bluejets

    3,365
    673
    Oct 5, 2014
    Maybe use h bridges?
     
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    You don't specify the load, but if it's a hundred mA or so, you can probably get away with some small mosfets in TO-92 packages (similar to the transistors you're likely using).

    For the N channel, a 2N7000 would work, and for the P channel, a ZVP2106A would probably be fine.

    A more generic solution is to search your favorite retailer (digikey, mouser, etc.) for an N channel mosfet in a to-92 package with an Rds(on) of about 5Ω or less, a Vgs of 20V or more, and an Ids of 200mA or greater. FOr the P channel mosfet, look for Rds(on) of about 5Ω or less, a Vgs of -20V or more, and an Ids of -200mA or greater.

    with an Rds(on) of 5Ω, a BJT may be better at even 100mA. If you search for devices in a TO-220 package with Rds(on) of 0.1Ω or less they will perfom better. 9V of Vgs should be fine for most of these, selecting "logic level" mosfets will ensure that it is.
     
  4. WHONOES

    WHONOES

    635
    122
    May 20, 2017
    Might I suggest using an IRF530 for the N device and its compliment an IRF9530 for the P device.
    Both can be obtained from Newark Element 14 for $1.39 and $0.95 respectively.
    They are both TO 220 parts and will probably need to be mounted on a small heat sink with suitable insulating pads and washers.
    Newark will also have data sheets available on line.
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    If you are using this arrangement with mosfets that have very low on resistance and a power supply capable of large currents, there is the potential for damaging shoot-through.

    If you're just using a small 9V battery, you may not even notice anything other than a brief glitch in the voltage.
     
  6. WHONOES

    WHONOES

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    122
    May 20, 2017
    Agree with (*steve*).
     
  7. Audioguru

    Audioguru

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    Sep 24, 2016
    Your Mosfets are shown backwards as source followers instead of as switches. The source of the P-channel Mosfet should connect to the positive supply and the source of the N-channel Mosfet should connect to 0V.
    It would be obvious that the body diodes in each Mosfet are shorting the 9V battery but the hard-to-see negative Falstad dotted schematic does not show the body diodes.
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    I agree. Wherever possible I always try to use schematic symbols showing the body diodes.

    Even if you intend to wire then up the right way, the easiest drafting error with MOSFETs is to draw them upsidedown. And that's going to confuse or mislead people.
     
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