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Driving the base of a transistor with the output of a 4017

Discussion in 'General Electronics Discussion' started by signalman72, Mar 29, 2014.

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  1. signalman72

    signalman72

    57
    6
    Jan 26, 2014
    Is it acceptable to just directly drive the base of a BJT(s) from the outputs of the 4017 decade counter, or should I use a resistor before the BJT? I plan on using the 3904. Thanks in advance.
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    No, generally it is not acceptable to do this in the normal "common emitter" configuration you'll likely use.
     
  3. cjdelphi

    cjdelphi

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    Oct 26, 2011
    Not without maxing out the current from 4017 from each pin
     
  4. signalman72

    signalman72

    57
    6
    Jan 26, 2014
    Thanks for the replies. I used a 1k resistor before the 3904. I'm powering the 4017 with a 9 volt battery. The current draw of the 3904 with the resistor is about 6.5 mA, so I'm safe. Without it was a little over 20 mA.
     
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