Optocoupler (opto-couplers) commonly used in the circuit as a feedback signal for use, especially in the security considerations, who can not connect two conductors of the circuit, as a circuit bridge purposes. Most of the switching power supplies, are the use of optocoupler good signal transmission characteristics, and to isolate the two circuits. Generally speaking, one side of the circuit should be the safety extra-low voltage circuit should be maintained to enhance insulation, incorrect use of opto-coupler bridge circuit might lead to insulation failure, in severe cases are more likely to lead to a sense of electrical accidents, it it very important.