Led flasher circuit (ne555n)

Discussion in 'General Electronics Chat' started by lubnaan90, Feb 2, 2010.

  1. lubnaan90

    Thread Starter Active Member

    Jan 13, 2010
    196
    2
    Planing to make a led flasher circuit out of NE555 ,
    My question is,is it possible to make the circuit work on a 14volt , 0.5 amp transformer.
    Do i need to change the POT or any other components .
    Any help will be deeply appreciated.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    The device is only able to operate with a DC voltage. You will need to rectify and filter the transformer output (unless it's a DC wall transformer).
     
  3. lubnaan90

    Thread Starter Active Member

    Jan 13, 2010
    196
    2
    Ofcourse , i am using a rectifier chip , like the one shown below .i have etched a special place to solder the same on the PCB.
     
  4. lubnaan90

    Thread Starter Active Member

    Jan 13, 2010
    196
    2
    i have almost finished etching , will clean the pcb & solder components with in 5 mins , will keep updated .
     
  5. lubnaan90

    Thread Starter Active Member

    Jan 13, 2010
    196
    2
    DONE !
    finished making the circuit ,
    seems something is wrong ,
    The circuit seems to work fine (Led Blinking) on a 12v .5amp wall DC adapter.
    but doesnt seem to be working (led not blinking , just steadily lit) on the transformer (14v .5amp) .
    Note: I have used the rectifier but not used a filter (since i dont have a capacitor wth me now) , can that be the problem ?
     
  6. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    The circuit will not work without the capacitor.

    If you are using a 14VAC transformer, you must also use a voltage regulator after the filter capacitor, or you will quickly burn out your 555 timer.

    I will guess that you will have about 19v to 24v on the filter capacitor, which is over the limit for your timer.
     
  7. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,348
    Hello,

    Without the buffer capacitor the DC voltage afther the rectifier will be pulsed.
    The 555 is every time starting again.
    You say you want to use a 14 Volts transformer.
    Use a 1000 uF / 35 Volts capacitor as a buffer.
    The rectified and buffered voltage will be about 1.4 X higher, so 14 X 1.4 is about 20 Volts.
    The maximum voltage for a 555 is about 15 Volts.
    You could use a LM7812 to stabelize the volatege back to 12 Volts.

    Greetings,
    Bertus
     
  8. lubnaan90

    Thread Starter Active Member

    Jan 13, 2010
    196
    2
    Thank you all for your interest
    Can I use L7812C Instead of LM7812 ?
     
  9. lubnaan90

    Thread Starter Active Member

    Jan 13, 2010
    196
    2
    SUCESS !!!!! i have successfully finished the Circuit .
    Thank you ,guys , really appreciate your help .
     
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