I am trying to measure the current through the MOSFET switch M1 using low side shunt resistor method (on MCLV-2 dev. board). I can read the signal `Vout' on the analog input of a dsPIC33F MCU. I believe that the capacitors are there to filter high frequency switching noise and clean up the measurement. Converting the ADC reading from MCU to a meaningful current reading in amperes requires solving this circuit. So I used a simplified circuit to apply the circuit theory to solve for the voltages. I arrived at the simplified circuit using the fact that in steady state the capacitor will behave as an open circuit. I came up with the following equations:
Vn = Vp (negative feedback) (V1 - Vn)/2K = (Vn - V3)/30K (KCL at node Vn with shown current direction) (Vref - Vp)/30K + (V2 - Vp)/2K = 0 (KCL at node Vp with shown current direction)
My questions are: (1) Is the simplified circuit correct? (2) Are these equations correct? (3) Do I need knowledge of
V1' andV2' for solving this circuit? Any other help regarding this will also be greatly appreciated!
The schematics of the original and simplified circuit are shown below.