Circuit for converting a non-live zero current signal to a live zero DC output signal

摘要

A circuit is coupled to an external power supply and is coupled to a non-live zero, two wire DC current transmitter (e.g. 4-20 MA output) for converting such current to a live-zero DC output current signal (e.g. 0- 20 MA output) and for powering such transmitter. The circuit has a first current to voltage converter for converting the transmitter current signal to a voltage signal, and a second current to voltage converter coupled to receive the circuit output current signal and an offset current from an offset current source for converting the sum of the circuit output and offset currents to a second voltage signal. A comparator is used for comparing the first and second voltage signals to provide the live-zero output current signal representative of the non- live zero transmitter signal. The circuitry can also provide isolated power to the transmitter and feedback (closed loop) control of such power.