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operational amplifier problem shunt current measurment

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yassin.kraouch

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i have a problem with my circuit : i have to calculate the current throught the shunt resistor ( each shunt have a value of 5 m ohm, so the value is 20 mohm ) the current is 4A and the voltage is 80 mV and the gain is 10, the pin 1 of J2 is the GND, the pin 3 of J2 is VCC, the pin 2 is the input of the voltage to amplifie, when i test my circuit i have no voltage that has been amlpified, have you an idea about this ?

 

Circuit has an error : LM324 pin 2 should be between R5 & R6

Connector J2 pin 1 GND & measured current - , pin 2 measured current + , pin 3 IC power supply
 

I mean , when i look your drawning.......
J2 pin3 is positive supply to IC
pin2 is measured current input +
pin1 is negative supply to IC (gnd) and measured current input - (gnd)
ie. measured current flows from pin2 to pin1
 

yassin.kraouch said:
i have a problem with my circuit : i have to calculate the current throught the shunt resistor ( each shunt have a value of 5 m ohm, so the value is 20 mohm ) the current is 4A and the voltage is 80 mV and the gain is 10, the pin 1 of J2 is the GND, the pin 3 of J2 is VCC, the pin 2 is the input of the voltage to amplifie, when i test my circuit i have no voltage that has been amlpified, have you an idea about this ?

Click to expand...

When you connect the resistors properly (as you have done in https://www.edaboard.com/threads/220637/ ) then the gain for the non inverting amplifier will be 1+(R6/R5) which is 1+10=11
In your previous thread both me and FvM have pointed that mistake but you keep repeating it.

Alex
 

Yes alex i know that the gain is 11 but i write always 10, don't worry about that.

---------- Post added at 17:18 ---------- Previous post was at 16:06 ----------

i have another question about the shunt resistor, it is not a low value 20 m ohm ?
 

I have used a 20m ohm in the past with a stepper motor but the gain I have used was 50 , so the output was 1v for each Ampere.
It depends on what you want, a small shunt resistor will heat less and will not alter the circuit operation (the 20m ohm is almost like a short)

Alex
 

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