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MOSFET help PLEASE! - Page 2 — Parallax Forums

MOSFET help PLEASE!

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  • QuadrtrFlyrQuadrtrFlyr Posts: 73
    edited 2013-04-06 17:14
    Ahh understood, the 2N2222 by itself also works well just like PJ Allen demonstrated. What are the load current limits for both setups? I am assuming pretty similar.. Now I am unsure as to which setup I should use...

    Robert
  • KC_RobKC_Rob Posts: 465
    edited 2013-04-06 17:20
    Ahh understood, the 2N2222 by itself also works well just like PJ Allen demonstrated. What are the load current limits for both setups? I am assuming pretty similar.. Now I am unsure as to which setup I should use...

    Robert
    I don't think load current capability is really an issue here. How long does the motor run at a time? Is the 2N2222 getting hot (very warm)? Probably not, so just go with it.
  • QuadrtrFlyrQuadrtrFlyr Posts: 73
    edited 2013-04-06 17:23
    Very short runtime so no heat generated by the 2N2222. I guess I will go with that method.. I very much enjoyed learning about the complexity of you circuit though
  • KC_RobKC_Rob Posts: 465
    edited 2013-04-06 17:25
    Very short runtime so no heat generated by the 2N2222. I guess I will go with that method.. I very much enjoyed learning about the complexity of you circuit though
    No problem. Next time you'll know better how to select the right MOSFET too. :)
  • jmgjmg Posts: 15,173
    edited 2013-04-06 19:13
    KC_Rob. It works beautifully!! I have found that when 3.3V is applied to the base of the BJT the load turns off and when 0V is applied to the base of the BJT then it turns back on! Is this correct??
    ...
    At the moment, the BJT is drawing .34mA to keep the load from running which isn't too bad I
    ...

    Err, you DO have a Series base resistor, between the Prop Pin, and the BJT base, right ?

    If your load is ~ 20mA, and you want a saturation gain of 10, that is about a 1K series resistor.

    You can drive from 330 ohms, but for a 20mA Load you do not really need to.
  • KC_RobKC_Rob Posts: 465
    edited 2013-04-06 20:57
    jmg wrote: »
    Err, you DO have a Series base resistor, between the Prop Pin, and the BJT base, right ?

    If your load is ~ 20mA, and you want a saturation gain of 10, that is about a 1K series resistor.

    You can drive from 330 ohms, but for a 20mA Load you do not really need to.
    Correct. That would apply to the 2N2222 circuit just a few comments above, however. The OP tried for starters to switch a IRF510 MOSFET directly from a Prop pin, then at some point later still a 2N2222 became an option, which is what he ended up using -- I think.
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