MCP617 current sensing

Discussion in 'The Projects Forum' started by mah, Mar 6, 2014.

  1. mah

    Thread Starter Active Member

    Mar 15, 2010
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    i used MCP617 to sense current , i used the configuration in the attached file while Rf=1 KΩ , RG=20 Ω and Rsense is existed in this link i think its value is around 6 m Ω .Gain should be Rf/RG = 1000/20 =50 i don't know what is VlM so i didn't add it in calculation i connect it to ground as i used single supply op amp but when i connected the circuit the output was reltaed to gain 1000 . do i have any problem in connection ?
    I used power supply instead of the battery , op amp has separate supply
    [​IMG]

    the above circuit existed in mcp607 datasheet . in my circuit Vlm is connected to the ground of the power supply (battery in the above ). so where is the error ? .
     
    Last edited: Mar 6, 2014
  2. Brownout

    Well-Known Member

    Jan 10, 2012
    2,375
    998
    Please show your circuit. I don't understand your explanation of how vlm is connected. Please show a drawing.
     
  3. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
    348
    If Vlm is connected to the power supply ground, there will be no load current through Rsen. Move the power supply ground to the left side of Rsen and see what you get.
     
  4. mah

    Thread Starter Active Member

    Mar 15, 2010
    276
    2
    i know i didn't connect it to -ve of power supply . the -ve is connected to 0ohm terminal and the other terminal is connected to VLM
     
  5. mah

    Thread Starter Active Member

    Mar 15, 2010
    276
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    i tested the attached circuit again but i forgot to connect pin3 ( red circle ) the chip got hot and burnt up for the second time . . i don't know why. may be because the ground of supply +5 v of the op amp was connected to pin3 instead of ground , could that be the reason as i read in datasheet its analog input Vss-0.3 max . could that wiring applied -5v on the input ?. also i measured the signal on zero ohm resistor it was 8.3 mv the output was .83 volt which mean that the gain is 101 not 51 however gain=1+1000/20 = 51 , i also tried another resistor and i got the same results the output multiplied by 2 ,i tried lm358 and it give the same results.
     
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    Last edited: Mar 9, 2014
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