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circuit using LM339

Discussion in 'General Electronics Discussion' started by cute109, Oct 9, 2010.

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  1. cute109

    cute109

    6
    0
    Oct 8, 2010
    i want to use LM339 as a voltage comparator for switching a relay at 25V but i am having a problem in the circuit.can anyone help me for the circuit?
     
  2. Militoy

    Militoy

    180
    0
    Aug 24, 2010
    Are you trying to switch a relay with a 25 (24) volt coil – or are you trying to switch 25V using the comparator to drive a relay? Either way, I’ve found that that for me, the simplest way to interface a relay with a comparator is to run the comparator in TTL mode – at 5VDC – and interface the relay using an ON Semi MDC3105LT1G relay driver. If all you have is a 25V source, you may have to add a simple 3-terminal regulator to supply the comparator and the relay / driver with 5V. The tiny 3-terminal relay driver really saves space and component count though – and I’ve found them very useful in my robotics applications.
     
  3. cute109

    cute109

    6
    0
    Oct 8, 2010
    i have limited resources and i cant get relay driver ic.i want to build it more simply in least cost as possible.
     
  4. NickS

    NickS

    367
    0
    Apr 6, 2010
    then you drive a transistor with the comparator. I will try to throw a schematic together for you but please explain better exactly what the 25V is for and what other voltage rails you have available if any.
     
  5. cute109

    cute109

    6
    0
    Oct 8, 2010
    i want to use this circuit for cutting out the supply line to the inverter sensing the battery voltage because i have the solar power for charging the battery in days.below 25V of the battery i want to charge it using inverter and if greater than 25V i want to cut out ac line in inverter input.
     
  6. cute109

    cute109

    6
    0
    Oct 8, 2010
    previously i use transistor to drive the relay but once relay switched at 25V DC it didnot come back at the voltage lower than 25 V so i am trying to use comparator.but i dont have enough knowledge about comparator.
     
  7. NickS

    NickS

    367
    0
    Apr 6, 2010
    Right, so you need the comparator to change states but the comparator cannot supply enough current to drive the relay coil(probably). So you buffer the comparator with the higher current transistor.
     
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