V supply and output of LM393

Discussion in 'General Electronics Chat' started by Pitsa, Aug 18, 2011.

  1. Pitsa

    Thread Starter New Member

    Aug 18, 2011
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    I new to IC, anybody can help is much appreciate.

    We use 15V supply to Vcc pin of LM393 and tied 36Vdc(with pull up resistor 10K) to open collector. Can we do this or any application issue on this?
    Thanks.
     
  2. #12

    Expert

    Nov 30, 2010
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    First answer, read the datasheet.
    You didn't provide one, so I did.
    Second answer: The datasheet says the LM393 can survive 36 volts.
     
  3. SgtWookie

    Expert

    Jul 17, 2007
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    What value resistor did you use on the output?

    The minimum value you should use would be 6k; that would cause the output to have to sink 6mA to get to 0v, which is as much as you should expect it to sink.

    36v is the absolute maximum voltage for the supply. You really should not operate the IC at its' absolute maximums. I suggest that you use something like a Zener diode on the output so that the output pin doesn't exceed ~33v, which is roughly 90% of the maximum.
     
  4. Pitsa

    Thread Starter New Member

    Aug 18, 2011
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    Pls correct me if I wromg, if we tied 36V to output and supply 15V to Vcc of LM393, it may exceed absolute maximums on the output side so I have to reduce output supply voltage about 90% of the maximum ~ 33, it would be great if you can recommened the Zener diode for output side. thank for your help much appreciate.

    BB
     
  5. SgtWookie

    Expert

    Jul 17, 2007
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    1N4752, DFLZ33, BZX84C33, and many other 33V Zener diodes would work.

    How high do you need the output voltage to go?

    You could take care of the problem by just using the 15v supply to attach your pull-up resistor to.
     
  6. Pitsa

    Thread Starter New Member

    Aug 18, 2011
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    Beside output voltage exceed absolute maximums on the output if we supply 36V, is there any concern if we use differnce voltage level between supply voltage on VCC(supply 15V) and output supply(~33V)? because I found in most application circuit used same voltage level for VCC and output supply.

    Thanks
     
  7. #12

    Expert

    Nov 30, 2010
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    I guess I typed that too fast. I'll try again: The datasheet says the chip will survive 36 volts. 36 volts does not exceed the absolute maximums on the output.
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    To which I'd replied earlier:
    And I'll stand by that statement. Just because it will survive 36v, does not mean that you should operate it continuously at 36v. 36v should be regarded as an exceptional case.
     
    Last edited: Aug 22, 2011
  9. #12

    Expert

    Nov 30, 2010
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    Sorry, wookie. I wasn't addressing you with that post. I was addressing the OP's repeated reference to "exceed absolute maximums". 36 volts does not "exceed absolute maximums". It isn't smart to run a chip at exactly the absolute maximum, but OP seems to be fixated on whether 36 volts will "exceed absolute maximums".
     
  10. Pitsa

    Thread Starter New Member

    Aug 18, 2011
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    Any effec if we run the part(LM393) with difference voltage level, VCC(15V) and Vo(36V)?
     
  11. #12

    Expert

    Nov 30, 2010
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    Yes. The effect will be that it works.
     
  12. Pitsa

    Thread Starter New Member

    Aug 18, 2011
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    #12

    Thanks.
     
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