10V overvoltage protection circuit

Discussion in 'The Projects Forum' started by radetonator, Apr 27, 2012.

  1. radetonator

    Thread Starter Member

    Aug 1, 2011
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    I want to use SCR to build a 10V overvoltage protection circuit. The circuit should be able to turn on and off SCR. Does any one know how to design the circuit?
     
    Last edited: Apr 27, 2012
  2. lightingman

    Senior Member

    Apr 19, 2007
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    You mean a crowbar...

    You can use a comparator (LM311) to sense the voltage and trigger the SCR. If you are protecting a DC circuit, you cannot turn off the SCR once it is conducting. You would have to switch the unit off and on again to reset it.

    Dan.
     
  3. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    You need to provide more details, especially what component / circuit you want to protect. A schematic helps too.
     
  4. BillB3857

    Senior Member

    Feb 28, 2009
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    If you are using the SCR in a crowbar mode you MUST have a means of either limiting the current to a value within the specs of the power source/wires/SCR/etc or a properly sized fuse. Simply shorting the output of the power supply is not a great idea. As stated earlier, once the SCR is triggered it will remain in an ON state until power is removed from it.
     
  5. CDRIVE

    Senior Member

    Jul 1, 2008
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    Last edited: Apr 29, 2012
  6. radetonator

    Thread Starter Member

    Aug 1, 2011
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    to protect a resistance load.

    The problem is how to turn off the SCR. Can SCR be turned off by rail-rail op amp?
     
  7. radetonator

    Thread Starter Member

    Aug 1, 2011
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    How to limit the short circuit current without using fuse?
     
  8. BillB3857

    Senior Member

    Feb 28, 2009
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    Like stated before, more information is needed. Does your power supply have current limit capability? Is the load on the power supply fairly constant or does it vary a lot? What percentage of the power supply capacity are you actually using at the output? The devil is in the details. The more information you provide, the better the answers will be. A drawing would be a great help.
     
  9. radetonator

    Thread Starter Member

    Aug 1, 2011
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    The power supply does not have current limit capability.
    Constant resistant load.
    70% of the power supply capacity.

    It would be much easier if SCR can be turned off by rail-rail op amp. Is it possible?
     
  10. crutschow

    Expert

    Mar 14, 2008
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    As you have been told by others, an SCR acts as a latch and the only way it can be turned off is by stopping the current flow through it. An op amp, rail-rail or otherwise, can not do that.

    If you want a device that can be shut off then you will need to use a power transistor, either a BJT or a MOSFET.

    You can limit the short circuit current with a resistance in series or a current-limit or current-limit foldback transistor circuit. Goggle will find you many of those.
     
  11. radetonator

    Thread Starter Member

    Aug 1, 2011
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    Thanks.
    If a LED has to be turned on and off by SCR, what circuit should be employed?
     
  12. crutschow

    Expert

    Mar 14, 2008
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    If the LED is powered by steady-state DC then an SCR circuit will not work. If it's powered from rectified, unfiltered AC then an SCR will work.

    What is the power source for the LED?

    Why this insistence on using SCRs? :confused:
     
  13. radetonator

    Thread Starter Member

    Aug 1, 2011
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    haha. I wanna try to use SCR. If using MOSFET, there would be no problem.

    yes, the power source is a 10V DC supply. At initial stage, i will use an adjustable DC power supply.
     
  14. CDRIVE

    Senior Member

    Jul 1, 2008
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  15. MrChips

    Moderator

    Oct 2, 2009
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    There is a simple way to turn off an SCR.
    It is called a fuse. The SCR trips. Fuse blows. SCR resets itself.
    Works every time like a charm.
     
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