
21-11Current Measurement
has found a new life in the form of dedicated integrated circuit chips that produce a ground-referenced
measure of the voltage across a shunt in the positive power rail.
Referring to Figure 21.8, the current from a power source drives a changing load via a shunt resistor
R
s
, which is chosen to drop 10–100 mV or so at the maximum current to be measured. e load current
creates voltages V
r
and V
s
with the dierence between them equal to the load current A
l
times the resis-
tance R
s
. e operational amplier requires that the voltage at its inverting input match the reference
voltage V
r
, which it accomplishes by turning on ...