A circuit with good linearity based on standard optocouplers

This article presents a circuit with good linearity based on standard optocouplers. The circuit takes advantage of inverse feedback to improve the linearity. It chooses two ordinary optocouplers of same characteristic. One phototransistor is typically used in a feedback mechanism to control the LED (light-emitting diode) drive current which has the effect of compensating for the LED's non-linear time and temperature characteristics. The other output phototransistor is used to provide the galvanic isolation between the input and output circuit. Simulate the circuit in Multisim, the results show that the circuit has good linearity and it can be used not only in DC circuits, but also in AC circuits of low frequency.