The current in the feedback loop depends on the voltage and Ri. This applications where we need to pass a constant current through a load and hold it constant despite any changes in load resistance or load voltage. When the load does not have to be grounded, we simply place the load in the feedback loop and control both input and load current from this circuit.
This circuit shown in figure voltage to current converter with floating load. The voltage to current converter can be used in such applications as low voltage dc and a voltmeters, diode match finders light emitting diodes (LEDS) and zener diode tester.
This circuit diagram Figure shows a voltage to current converter in which load resistor RL is floating (not connected to ground). The input voltage is applied to the no inverting input terminal and the feedback voltage cross R1 drives the inverting input terminal. This circuit is also called a current series negative feedback amplifier because the feedback voltage across R1 (applied to the inverting terminal) depends on the output current i0 and is in series with the input difference voltage vid.