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Can anyone explain me this circuit

  1. Feb 4, 2015 #1
  2. jcsd
  3. Feb 4, 2015 #2

    NascentOxygen

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    Staff: Mentor

    This is a homework exercise?

    It should be in the homework subforum.
     
  4. Feb 4, 2015 #3
    no, this is my project for school
     
  5. Feb 4, 2015 #4

    NascentOxygen

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    What is the circuit supposed to do?
     
  6. Feb 4, 2015 #5

    Svein

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    Seems a bit odd. If you connect the battery when there is no light on the LDR, the thyristor will turn on, the LED will start glowing and there will be a click in the speaker. When the LDR gets illuminated - it depends on the thyristor and the speaker (a thyristor will not turn off if the load current is large enough).
     
  7. Feb 4, 2015 #6
    this is the circuit of a laser security system
     
  8. Feb 4, 2015 #7
    Can you explain in more detail?
    Thanks
     
  9. Feb 4, 2015 #8

    Svein

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    From http://en.wikipedia.org/wiki/Thyristor :
    Thyristors have three states:

    1. Reverse blocking mode — Voltage is applied in the direction that would be blocked by a diode
    2. Forward blocking mode — Voltage is applied in the direction that would cause a diode to conduct, but the thyristor has not been triggered into conduction
    3. Forward conducting mode — The thyristor has been triggered into conduction and will remain conducting until the forward current drops below a threshold value known as the "holding current"
     
  10. Feb 5, 2015 #9
    Another thing I would like to add is the thyristor is BT-169
     
  11. Feb 5, 2015 #10

    NascentOxygen

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    What can you tell us about the Speaker?

    Have you bought the components? How does the laser get used?
     
  12. Feb 5, 2015 #11

    Svein

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    Look at http://www.nxp.com/documents/data_sheet/BT169_SER.pdf [Broken]

    A slight problem: BT-169 is not specified for DC operation.
     
    Last edited by a moderator: May 7, 2017
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