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NE555 R-S bistable IC

Discussion in 'General Electronics Discussion' started by Integrator741, Nov 27, 2013.

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  1. Integrator741

    Integrator741

    125
    4
    Jun 16, 2013
    Hello guys,

    I need your help to understand whats happening inside R-S bistable part of NE555 chip.

    Is it simple Cross-coupled NAND gates or something else?

    Because if it would be cross-coupled nand gates the chip would have two outputs right? or am i too ignorant and I missed out something...?!

    [​IMG]

    Thanks.
     
  2. jpanhalt

    jpanhalt

    426
    4
    Nov 12, 2013
    Note that when the output is low, the discharge capacitor is ON to discharge the timing capacitor. So, there are two, complementary outputs from the flip-flop.

    Capture.PNG

    John
     
  3. Harald Kapp

    Harald Kapp Moderator Moderator

    9,549
    1,973
    Nov 17, 2011
    Have a look at this kit. It includes complete internal schematics.
     
  4. jpanhalt

    jpanhalt

    426
    4
    Nov 12, 2013
    What a fun way to waste some time.

    Along the same line of fun but useless, I have occasionally suggested to individuals who were desperate for a FYP that they program a 12F6xx chip to emulate the 555. Of course, the power pins are reversed. HighTechChips, Inc. (http://www.hightechips.com/ ) has already done some of that work.

    That kit you link to led me to revisit my 555 folder, and I came across this drawing:
    Capture2.PNG

    It shows the flip-flop in vivid color. The source was a web page created by Glen Williamson of the School of Engineering at North Carolina State University. Unfortunately, I couldn't find the actual link any longer and hope that credit is sufficient.

    John
     
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