logic breaker design

Discussion in 'Homework Help' started by kobi_technion, Aug 1, 2015.

  1. kobi_technion

    Thread Starter New Member

    Aug 1, 2015
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    hi all.
    need an urgent help with design. please assist.
    i need to design a logic circuit that takes feedback from other circuit about an over-voltage and cut it off permanently.
    the problem now is that it cuts it off and when voltage reduce to normal level it power it again.

    can use only logic gates and flip flops for that.

    many thanks for helpers.
     
  2. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Post a schematic of what you have now and we probably can figue out a modification. It sounds like an additional latch would hold the off state when the input returns to normal.

    ak
     
  3. strantor

    AAC Fanatic!

    Oct 3, 2010
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    crowbar circuit
     
  4. kobi_technion

    Thread Starter New Member

    Aug 1, 2015
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    sketch attached.
     
  5. kobi_technion

    Thread Starter New Member

    Aug 1, 2015
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    no fuse or diodes allowed. tnx anyway.
     
  6. strantor

    AAC Fanatic!

    Oct 3, 2010
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    "Permanently" implies a fuse action.
    say circuit A cuts power to circuit B.
    so what action is expected to restore power to circuit B?
    if you cut all power to circuits A and B and then reapply power, should it reset (supply power to circuit B) or should power still be removed from circuit B upon re-powering?
     
  7. crutschow

    Expert

    Mar 14, 2008
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    What else is "not allowed"?
     
  8. kobi_technion

    Thread Starter New Member

    Aug 1, 2015
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    well basically only opamps, res. cap. cond. trans. and logics like ff and gates.

    maybe its hard to understand from the sketch what the purpose of every sub circuit,
    the main goal is to model a sensor that in t=0 send a step voltage of 1v that stops the motor.
    till then the motor need to have 12v. the other thing is to stop the motor when current through it exceeds 1A for a duration of 10ms.
    so, the upper amp is taking care of the sensor and the 2 others evaluate the voltage (current) and the delay and then with
    gates i stop the motor with the transistor.

    the problem is that when the motor stops because of overcurrent, it starts again when current falls.

    need to find away to stop it completely.
     
  9. WBahn

    Moderator

    Mar 31, 2012
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    As others have indicated, use a latch. When you detect an overcurrent you set a latch that disables the power and to re-enable it requires that you reset the latch (through whatever mechanism makes sense for your application).
     
  10. kobi_technion

    Thread Starter New Member

    Aug 1, 2015
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    hmm... what is a latch? btw cant have a clock and pls can you give a little guidance about how i connect it?
     
  11. WBahn

    Moderator

    Mar 31, 2012
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    A flip flop is a form of latch. If you can't have a clock, then you simply generate your clock signal like any other logic signal (though you need to be very careful about glitches).

    If you take a DFF and tie the D input HI, then if your overvoltage logic produces a low-to-high transition on the clock input the DFF will be latched HI. The only way to get it to go LO is to assert the RESET signal using different logic.
     
  12. kobi_technion

    Thread Starter New Member

    Aug 1, 2015
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    thanks for the help so far. tried and couldn't make it work.

    but.. i've found a way to simplify my problem: i need to design a logic circuit that goes like this:

    k k+1 k+2 k+3 ........
    input 1 0 any any ......
    output 1 0 0 0 .......

    while k is the step.
    i have no experience in design so sorry for the ignorance.
     
  13. WBahn

    Moderator

    Mar 31, 2012
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    Saying, "tried and couldn't make it work" just does not give us enough information to feed into our crystal balls. Seriously, how can we POSSIBLY tell what you are doing wrong when you refuse to show us what you are doing at all?

    So show your best attempt to implement this using a DFF. Remember that you have things called inverters, too.
     
  14. kobi_technion

    Thread Starter New Member

    Aug 1, 2015
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    finally could pull it off with sr ff and d ff.
    thank you all for help.

    cheers.
     
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