–48V Low Side Precision Current Sense

This amplifier configuration is essentially the complementary implementation to the classic high-side configuration. The op amp used must support common-mode operation at its lower rail. A “floating” shunt-regulated local supply is provided by the Zener diode, and the transistor provides metered current to an output load resistance (1kΩ in this circuit). In this circuit, the output volt-age is referenced to a positive potential and moves downward when representing increasing –48V loading. Scaling accuracy is set by the quality of resistors used and the performance of the NPN transistor.