Resistor divider (R1 and R2) is
implemented to limit the maximum voltage at the non-inverting input,
Vin+, and sense resistor, R5, at full-scale.
For an op amp that is not
rail-to-rail input (RRI), a voltage divider is needed to reduce the input
voltage to be within the common-mode voltage of the op amp.
Use low resistance values for
R5 to maximize load compliance voltage and reduce the power
dissipated at full-scale.
Using a high-gain BJT reduces the
output current requirement for the op amp.
Feedback components R3,
R4, and C1 provide compensation to improve stability.
R3 isolates the input capacitance of the bipolar junction
transistor (BJT), R4 provides a DC feedback path directly at the
current-setting resistor (R5), and C1 provides a
high-frequency feedback path that bypasses the BJT.
Use the op amp in a linear
operating region. Linear output swing is usually specified under the
AOL test conditions in the device data sheet.