Strange thing??comparator

Discussion in 'General Electronics Chat' started by nepdeep, Jan 24, 2013.

  1. nepdeep

    Thread Starter Member

    Sep 14, 2011
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    Hi, I was using comparator in my circuit for overvoltage protection...i applied the limited voltage from the function generator...performed some test of the circuit....after about 5 minutes the comparator blew....what could have been the problem...I donot see any reasons related to shorting...cause as far as i can think of i didnot touch the comparator....what could be the reasons....please help me find the bug

    The comparator has open drain ooutput
     
  2. debjit625

    Well-Known Member

    Apr 17, 2010
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    A full circuit diagram/schematic would be helpfull to debug the problem for us...

    Good luck
     
  3. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    What kind of load was the comparitor driving? What were your input voltages and supply voltages. What part number on comparitor?
     
  4. nepdeep

    Thread Starter Member

    Sep 14, 2011
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    supply voltage 15......
    input voltage 0 to 3.3....and
    ....
    i have the schematic uploaded forum.jpg
     
  5. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    On your diagram is marked: "both in the same package". The datasheet I has only one comparator per package.

    What was the voltage you applied to pin 3 of the upper IC?
    It must exceed than the power supply voltage.

    PS:Replace "mV" with "V".
     
  6. tubeguy

    Well-Known Member

    Nov 3, 2012
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    What type of signal where you applying from the function generator ?
     
  7. MrChips

    Moderator

    Oct 2, 2009
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    Put a 10kΩ resistor in series with the input.
     
  8. nepdeep

    Thread Starter Member

    Sep 14, 2011
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    PS:Replace "mV" with "V".

    the input is 2200[mV]
     
  9. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    So you are comparing 2.2V with 2.2V? I thought the purpose was to short the circuit on the right side of the 5k11 resistor whenever the input voltage is higher than 2.2V.

    If the maximum voltage you ever applied to the input is 2.2V I don't see a reason why it could have been damaged. Maybe there is a short somewhere.
     
  10. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    From post #4:
     
  11. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    The only thing I can think of is electrostatic discharge damage. I would add a resistor and a diode, as shown on the attached schematic.
     
  12. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    From post #8: 2.2V. :D

    Yeah I didn't see that first info.
     
  13. nepdeep

    Thread Starter Member

    Sep 14, 2011
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    ya the reference voltage is 2.2 v and if the input ranges from 0 to 2.2 ......so 2.2 is protection limit....next thing...i changed the comparator and is working fine now...but still couldnot find the root cause of the blown comparator...some possible scenarios....may be...!!
     
  14. Salaja

    New Member

    Jan 27, 2013
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    hmm. i've an idea, but i don't know how realistic it is...

    what if, for some reason, the feedback loop wasn't stable, which caused the op-amp's output to oscillate as fast as it could, and because it is connect to the gate of a mosfet with internal capacitance, the high frequency passed through the capacitor/mosfet, shorting the op-amp output to ground. so we end up with an op-amp trying to drive 15v into ground, which only results in it pumping so much current it blows due to it's internal resistance to the current surge.

    ...is this even possible? xD
     
  15. nepdeep

    Thread Starter Member

    Sep 14, 2011
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    ya this is quite clever possibility...i also doubt if it is possible though....current leakage from gate to source....but i was also thinking something like that like...it was souring huge current...
     
  16. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Sometimes components are bad or counterfeit that seem to work most of the time, but not to full specifications.

    Where did you get the comparators from? There's a possibility you received counterfeit ICs. They are everywhere, and make up for a decent chunk of the "Great deals" on eBay.
     
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