Cmos 4013

Discussion in 'The Projects Forum' started by djsfantasi, Mar 15, 2013.

  1. djsfantasi

    Thread Starter AAC Fanatic!

    Apr 11, 2010
    Looking at the datasheet, it appears that the Q output of a 4013 D-type flip flop cannot provide enough current to light an LED (looking at the value for Ioh, specified as only 2.25 ma at 9vdc).

    Yet, the same appears true for the output of a 4093 gate -

    And I've seen circuits with both ICs - - the 4093 directly lighting an LED and the 4013 using a transistor...

    What is correct?
  2. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    Did you happen to catch that commercial where they state "it has to be true because it's on the internet, and you can't put anything that's not true on the internet"???

    Well it's completely true! So those circuits MUST work.

    Checking the ABS-MAX (absolute maximum, or "Limiting values" as this sheet calls them) an output is limited to 10 mA, plenty to run a LED... not that I would build it that way.

    I'll use a micro output to run a LED as an indicator, these outs are rated for 25 mA and I don't go over 10 mA. Oft much less.
  3. djsfantasi

    Thread Starter AAC Fanatic!

    Apr 11, 2010
    OK, I figured it was too good to be true :)

    I am having trouble with LTSpice, but was wondering if the following schematic will light the LED when the Q output of the 4013 goes High. I know there is a lot missing, but assuming that the rest works - what happens when the Q output changes? I have a $100 order in my Mouser cart and would like to avoid going back for onesies and twosies...

  4. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
    Put a resistor between the output Q and the base of the transistor so you do not damage the transistor. The value of the resistor can be chosen so the current from the output Q is about 1/10th the current you want in the LED.

    R = (Vsupply - 0.7v)/I where the transistor requires 0.7v across its base and emitter to turn on.
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  5. djsfantasi

    Thread Starter AAC Fanatic!

    Apr 11, 2010
    Thanks for catching that.

    The LED is rated for 30ma continuous forward current, but 1/10th of that is 3ma and the 4013 Ioh is only rated for 2.2ma. So, running the LED at 22ma should be possible.

    The power supply is a 9vdc battery. The LEDs forward voltage is 3.6VDC. At 22ma, the current limiting resistor should be 270Ω (nearest standard value).

    Voh of the 4013 is ~8.95 volts less the .7 drop from base to emitter equals 8.25v. One tenth of 22ma is 2.2ma and the resistor to the base comes out to be 3.9κΩ (nearest standard value).

    Do these calculations appear correct?

  6. #12


    Nov 30, 2010
    Looks right to me.

    and remember, there is no law that says you have to run your LEDs at the maximum rated current.
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