Opamp Question

Discussion in 'General Electronics Chat' started by Dr.killjoy, Nov 24, 2013.

  1. Dr.killjoy

    Thread Starter Well-Known Member

    Apr 28, 2013
    1,190
    156
    I am working a constant current electronic load .. I was wondering if I could take one of the opamp and take the input and put it across a power resistor ( 1Ω 50 watt) and use it to measure the current in volts but to trigger high at say 3amp to a relay to shut everything down ?????





    Thanks
    Jason SR
     
  2. crutschow

    Expert

    Mar 14, 2008
    13,056
    3,245
    If the voltage is DC, then yes. You could use a comparator or op amp used as a comparator with a reference voltage of 3V to indicate the shut-down point.
     
  3. Dr.killjoy

    Thread Starter Well-Known Member

    Apr 28, 2013
    1,190
    156
    Here a schematic
    [​IMG]
     
  4. ScottWang

    Moderator

    Aug 23, 2012
    4,855
    767
    Comparator comparing nothing.
    What's your Voltage for load?
    What's your voltage for comparator?
    I was used an op amp to designed a similar function, but it's not likes that way.
     
  5. WBahn

    Moderator

    Mar 31, 2012
    17,777
    4,805
    This comparator will only tell you if the current in the sense resistor is positive or negative.

    You want a differential amplifier followed by a comparator (and, yes, they can be combined into one opamp circuit, but it is generally better to break up your functions into well defined blocks).
     
  6. tubeguy

    Well-Known Member

    Nov 3, 2012
    1,157
    197
    With an op-amp/comparator circuit you can use an even lower value, and therefore lower wattage sense resistor. Also, less voltage drop occurs for a given current through the sense resistor.
     
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