Warning light on led if a light-bulb breaks

Discussion in 'Homework Help' started by sirmax, Sep 1, 2010.

  1. sirmax

    Thread Starter New Member

    Apr 3, 2010
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    I am supposed to create a circuit that turns a light on and has a led indicator to tell if the light goes off. I can only use Zener-diodes and resistors along with a led to be used as a indicator if the light has broken. It sounds simple, but i haven´t got a clue on how to do this so any help would be highly appreciated.
     
  2. hobbyist

    Distinguished Member

    Aug 10, 2008
    764
    56
    Think in terms of a zener voltage regulator.
     
  3. BMorse

    Senior Member

    Sep 26, 2009
    2,675
    234
    Is this a DC operated Light? What voltage? What is the forward current and forward voltage of the LED you are going to use? Can you be more specific about your project and give more detail of the requirements and specs?
     
  4. sirmax

    Thread Starter New Member

    Apr 3, 2010
    8
    0
    yes this is Dc voltage and it would look something like this to begin with but i don´t know where to put the Zener-dioder and how to make it work the following way: When the light goes off the led will turn on as an indicator.
     
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  5. Georacer

    Moderator

    Nov 25, 2009
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    Here's a thought: If your light is battery operated, connecting the battery to the light will drop its voltage a little. So if you connect, in parallel to the bulb, a zener and a LED in series, they won't light when the bulb draws current. But when the bulb burns out, the zener will yield under the current flowing through it and will led the LED light up.

    But I need someone to confirm it. I' m very doubtful about it.
     
  6. n1ist

    Active Member

    Mar 8, 2009
    171
    16
    You also need a current-limiting resistor for the LED. Think about it this way:

    What's the voltage across the bulb when it is on?
    What's the voltage across the bulb when it is burned out?
    What voltage does the LED need to turn on?

    So as Georacer pointed out, you use the zener to set the trip point where the LED will turn on.
    /mike
     
  7. sirmax

    Thread Starter New Member

    Apr 3, 2010
    8
    0
    ok, i got this sorted...thank you guys for your help.
     
  8. Georacer

    Moderator

    Nov 25, 2009
    5,142
    1,266
    What did you finally do? How did you solve the problem?
     
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