Connect with us

What is going on.

Discussion in 'General Electronics Discussion' started by SB0202022, Nov 26, 2012.

Scroll to continue with content
  1. SB0202022

    SB0202022

    7
    0
    Oct 27, 2010
    Could some please help me understand what is going on in this circuit? I'm slightly confused. I know it is a circuit that flashes two LED's, but why does it alternate? What causes the two to alternate when each side has equal values?
     

    Attached Files:

    • AHHH.jpg
      AHHH.jpg
      File size:
      21.1 KB
      Views:
      226
  2. duke37

    duke37

    5,364
    769
    Jan 9, 2011
    Each side does not have equal values. They are similar but are sufficiently different to start things off. Look at component tolerances.
     
  3. Raven Luni

    Raven Luni

    798
    8
    Oct 15, 2011
  4. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    Agree, I have never seen an astable being called a flip-flop before.

    Bob
     
  5. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    The link was provided to explain 'why' the circuit acts as it does, as the OP asked, I though the site did a pretty good job of explaining why it functions...

    As for the 'proper' definition of 'flip-flop' (astable/bistable) that is certainly along the same lines, but a Google search will reveal that 'flip flop' has become quite a blurred generic definition...
     
  6. duke37

    duke37

    5,364
    769
    Jan 9, 2011
    Why use pnp transistors when npn are more common?

    Are the capacitors connected the wrong way round?
     
  7. Raven Luni

    Raven Luni

    798
    8
    Oct 15, 2011
    Probably for the same reason I would: Because they bought matched PNPs and NPNs in equal amount then ended up using more of the NPNs for various projects :p
     
  8. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,271
    Nov 28, 2011
    Yes they are, well spotted duke.
     
  9. duke37

    duke37

    5,364
    769
    Jan 9, 2011
    Another comment.

    This circuit drives the base from 0.6V forward to 1V or so less than the supply in reverse.
    The circuit will work well at lower voltages but may exceed the permitted reverse emitter/base voltage at 9V. A diode in each emitter lead is perhaps the best way to protect the trnasistors.
     
  10. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,271
    Nov 28, 2011
    Yes, 9V would be pushing it. The LEDs in the collector paths will reduce the voltage on each capacitor though. I'd estimate Vbe around 7V with a 9V supply.

    A poorly designed circuit on a random web site. Who would have guessed :)
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-