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Darlington strange behavior

Discussion in 'General Electronics Discussion' started by hyudryu, Mar 18, 2010.

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  1. hyudryu

    hyudryu

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    Feb 24, 2010
    Do the collector and emitter of a MJ10012 darlington transistor have a lot of resistance?
    I tried to discharge something and it was very slow at discharging
     
  2. Mitchekj

    Mitchekj

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    Jan 24, 2010
    It's a dynamic 'resistance.' It all depends on the base current. If it's saturated, it will be at the min 'resistance'. A darlington will have about twice the Vce drop of a normal transistor, by the way. What base current were you running? It doesn't need to be much to saturate a darlington pair, relatively. (I haven't looked at that particular component's specs, btw.)

    This 'drop' across the collector-emitter would be a rough equivalent to a FET's RDSon, which would be a closer analog of resistance.

    Edit: To expand, if you want to discharge something that way (as a switch?) then a darlington is NOT the way to go. A darlington is used for high gain, not low Vce drop. I'd use a very low RDSon FET. (Depending on current levels, of course.)
     
    Last edited: Mar 18, 2010
  3. hyudryu

    hyudryu

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    Feb 24, 2010
    The maximum my power suplly would give is 3.2A. But it has some sort of protection so when i connected 9V 3.2A onto the base, it would go to like 2V 3.2A When i connected it to a 9V battery as base, it did worse than a thyristor
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Perhaps this is the point at which you should tell us what you're trying to do.
     
  5. Mitchekj

    Mitchekj

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    Jan 24, 2010
    Agreed with steve... what're we doing here? Above and beyond "trying to discharge something." Something, like a big bank of caps? The confounded gauss gun, yeah?

    And, your supply dropped to 2V at 3.2A because the poor darlington was trying to sink all of that current through the base. Your supply went into constant current mode, since the required voltage to draw that was only 2V, according to your post, and the max your supply can push is 3.2A. If I understand you right, you're trying to drive this transistor with 9V on the base??? No, no, no... the base of a transistor should be driven with a CURRENT source, and reading the specs, 9V is above the max rated Vebo anyhow.

    That transistor has a max base current of 2A. You're going to melt it, if it's not already latently damaged.
     
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