Hi I am building a circuit to measure current draw from a load, I opted for a voltage follower with a transistor and a shunt in between, The transistor is needed to allow higher currents to flow through the load, here is my schematic:
The Op-Amp is configured with Negative Feedback, So as long as the Input Voltage plus the shunt voltage plus the transistor Vce is lower than the Collector Voltage, the transistor would be in saturation mode (I'm actually not sure).
If the BJT is in saturation mode, the voltage across the load would be exactly the same as the Input Voltage, also the current across the shunt is the same as the current across the load, allowing to sense the current with a differential amplifier across the shunt.
What I am not really sure is if I need to place a resistor between the Op-Amp Output and the base of the BJT, I think that the Op-Amp would compensate by itself, but idk.
So the actual question is if a resistor needed between the base of the BJT and the Op-Amp output.
This is the second stage for a DC Variable Voltage source.
This stage has three purposes:
-The first, to keep the voltage across the load equal to the input voltage.
-The second is to be able to measure the load current with a differential amplifier across the load
-The third to increase me maximum current that can be supplied to the load. Since the first stage is 1.5 Amps max, I would like to make this at least 3 Amp max