V G wrote:
> Why would I have an error if I can control the BJT by sensing the
> current through a current sense resistor?

Because the base current doesn't go thru both the battery and the sense
resistor.  For a NPN with low side current sense resistor, the base current
comes from elsewhere but runs thru the sense resistor.  The current as
measured by the sense resistor is therefore the battery current plus the
base current.  Since the base current is the battery current divided by the
transistor gain, this error gets less as the transistor gain is increased.


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