SCR as a Switch in back-up power

Discussion in 'Homework Help' started by samrat, May 6, 2008.

  1. samrat

    Thread Starter Active Member

    Apr 2, 2008
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    Need to understand how the SCR can act as a switch to trigger a back up battery of 12 volts ON when the power goes OFF...explanation with a circuit diagram would be really handy.
     
  2. mik3

    Senior Member

    Feb 4, 2008
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    what is the DC voltage output of the power supply?
     
  3. mrmeval

    Distinguished Member

    Jun 30, 2006
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  4. samrat

    Thread Starter Active Member

    Apr 2, 2008
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    Hi MIK3.. the output DC voltage is 12 volts from a rectifier cct that was stepdown from from a 240 v AC supply. The 12 volts should also be used to charge the 12 volt battery. The SCR should trigger the power switch to turn to the 12 volt battery once the main power is cut off. This 12 volt battery is for a standard lighting system at home that can operate on 12 volts.
     
  5. samrat

    Thread Starter Active Member

    Apr 2, 2008
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    I know that a SCR is triggered by a positive pulse and stays ON but for this assignment, it has to be triggered when the power supply is OFF. Thats where I am stuck.
     
  6. mik3

    Senior Member

    Feb 4, 2008
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    You can make things simpler if you forget the SCR and use a relay. The power supply will drive the relay when the power is on. When the power goes off the relay will release and connect the battery to the circuit you want. Is it possible or you have to do it with an SCR?
     
  7. samrat

    Thread Starter Active Member

    Apr 2, 2008
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    I have thought about the relay but a scr is what is needed to be used.
     
  8. mik3

    Senior Member

    Feb 4, 2008
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    Ok see the attachment then. But note that when the power comes back again on the power supply the SCR wont shut off. if you want you can replace the SCR by an NPN transistor as when the power comes back to release the relay. Or if you still want the SCR use a transistor in parallel with the SCR to reset it when power comes back.
     
  9. samrat

    Thread Starter Active Member

    Apr 2, 2008
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    Thanx Mik3..really appreciate it....
     
  10. samrat

    Thread Starter Active Member

    Apr 2, 2008
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    Mik3, the top right side of the diagram you sent was not very clear. Couldn't read the writing. Can you please specify??? thanx
     
  11. samrat

    Thread Starter Active Member

    Apr 2, 2008
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    Hey Mrmeval, can you please resend the web address that you sent? Couldn't find a link to the one that you sent earlier.
     
  12. mik3

    Senior Member

    Feb 4, 2008
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    The word on the left is 'power supply' , the word on the top is 'to the circuit' and the word on the right is 'battery'
     
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