My hardware design team have given me circuit to measure current consumed by load.I have to measure current consumed by Load using MCU ADC. Can someone explain what exactly this OP amp is doing ?
I am from software side & not a hardware expert.
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Sign up to join this communityMy hardware design team have given me circuit to measure current consumed by load.I have to measure current consumed by Load using MCU ADC. Can someone explain what exactly this OP amp is doing ?
I am from software side & not a hardware expert.
This is a classic diff amp circuit. In this case the circuit measures the voltage across R33, which is proportional to the current thru it.
The diff amp gives a single-ended voltage proportional to the difference between two input voltages. This is useful in that it allows the two input voltages to "float", meaning they can go up and down together without changing the output, since the difference between the inputs doesn't change.
For more details, ask your hardware design team or look up differential amplifier and current sense resistor.
You should ask your hardware team to provide you the transfer function (ADC voltage as a function of current). This is an entirely reasonable request and better than asking a bunch of strangers on the Internet.
R42 adds an offset of 454mV to the amplifier non-inverting input, which is multiplied by 11 (5.00V out at zero current) as seen at the op-amp output. That op-amp output voltage decreases by 1V/A of load current. The ADC sees half the op-amp output voltage.
So, my take on the transfer function is:
\$V_{ADC} = 2.5V - 0.5\cdot I_{LOAD} \;\;\; (0 \le I_{LOAD} \le 5A )\$.
Which you can easily re-arrange to find the load current given the ADC reading and ADC reference voltage.
It's a pretty straightforward (if sloppy in terms of potential accuracy) circuit but it's not your job to reverse-engineer their chum bucket of a design.