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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


    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

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


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


    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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