Single Trigger Pulse for IC 555 only when the system is turned ON using TI 431

Discussion in 'The Projects Forum' started by varundua, Jun 15, 2015.

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  1. varundua

    Thread Starter New Member

    Jun 15, 2015
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    Hey,

    I want to send a trigger pulse to IC 555 ONLY when the 230V AC supply (which gets converted to 12V DC using a Zener Voltage Regulator) gets turned ON. It would be something like when the power supply is turned ON, only at that time the trigger pulse is applied and during its operation there is no trigger pulse applied to IC 555.

    Is it possible to achieve this through TI 431? If yes, then how should I go about it?

    Thanks,
    Varun
     
  2. #12

    Expert

    Nov 30, 2010
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    Are you asking about a TL431?
     
  3. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    You can use an opto coupler to trigger the 555 ,use the tl431 to fire the led on, and the transistor to trigger the timer.
    Note the tl431 is an adjustable zener diode....also you can just use a resistor and capacitor on pin 2 to self trigger the timer on power up...
     
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  4. varundua

    Thread Starter New Member

    Jun 15, 2015
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    You mean to say using the 431 to fire the LED of optocoupler and the transister inside the optocoupler to trigger 555? Frankly speaking I've got less idea of how an optocoupler works.. tried a few websites quite a long back didnt understand though :p
     
  5. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Yes, the led lights up with the tl431, the transistor turns on when the led is lit inside, it shorts the Collector and Emitter together, just like a normal one.
     
  6. varundua

    Thread Starter New Member

    Jun 15, 2015
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    What I am actually required to do is charge up a solenoid coil for only 500ms using 230V ac supply which converts to a 12v dc supply using a transformer less zener voltage regulator which in turn goes to a IC 555. The output of 555 is applied at the gate of N channel E-MOSFET which acts as a switch. The Drain terminal of the mosfet is then connected to the coil which charges it up for only 500ms. The coil is also supplied with 230V ac. Is this feasible?
     
  7. crutschow

    Expert

    Mar 14, 2008
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    Is below what you wanted?
    It generates a single one-shot output when the 12V power is turned on.

    Pwr On One-shot.GIF
     
    Last edited: Jun 15, 2015
  8. varundua

    Thread Starter New Member

    Jun 15, 2015
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    Yeah but it's like the power is continuously turned ON although the trigger is applied only once when the power was turned ON.
     
  9. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    OUCH ,did you say transformerless psu!!!!!
     
  10. varundua

    Thread Starter New Member

    Jun 15, 2015
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    Haha yeah :p
    Want it to occupy less space and less cost as well :)
     
  11. crutschow

    Expert

    Mar 14, 2008
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    I showed it with the power turning off and back on but if you leave the power on, only one pulse is generated.
     
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  12. crutschow

    Expert

    Mar 14, 2008
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    That's also very dangerous since the circuit is not isolated form the mains power. :eek:
    That's not an acceptable circuit.
     
  13. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    So are you using a switched mode psu instead of a transformer?
     
  14. varundua

    Thread Starter New Member

    Jun 15, 2015
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    Ohh that's great.. will try implementing it to see its results :) Thanks a lot!

    So in that case can some other transformerless circuit be used for ac-dc conversion?
     
  15. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Yeah a switched mode psu...like a mobile phone charger.
     
  16. varundua

    Thread Starter New Member

    Jun 15, 2015
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    So an SMPS will be more cost effective than the one I mentioned? My mentor wants it at low cost and low space. I've heard SMPS provides one of the highest efficiency for ac-dc conversion?
     
  17. ScottWang

    Moderator

    Aug 23, 2012
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    Present time the forums still not allowed to discuss the transformerless issue, if you like to find some other ways to do then the discussion can be continuing, otherwise this thread will be closed, thank you.
     
  18. varundua

    Thread Starter New Member

    Jun 15, 2015
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    Ohh I'm sorry, I didn't know we are not supposed to discuss this transformerless issue. Won't discuss this issue further! :)
     
  19. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Its ok to use a Smps, and discuss it, its not allowed to use the transformerless psu that you were thinking of using, you can get an old phone charger or similar smps psu and use that.
     
  20. crutschow

    Expert

    Mar 14, 2008
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    I assume you can discuss it, just not post circuits or promote it. :confused:
     
  21. ScottWang

    Moderator

    Aug 23, 2012
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    Although I like to discuss it, but the rules is there, that is not I can decide, maybe in the future we can do that, who know, the world is changing all the time.

    Even we can discuss in Taiwan, but we still would not encourage the user to do without ee background.
     
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