Logic Output Opto-couplers are opto-couplers with a phototransistor output and are used to provide isolation between a high voltage circuit and a low voltage logic circuit. The transistor output allows for the opto-coupler to be used in applications where the circuit needs to be switched. The opto-coupler isolates the two circuits from each other by using a light source to transmit the logic output from one circuit to the other. The light source can be an LED, a laser, or an infrared source. The output from the logic circuit is then converted into a voltage level that is compatible with the high voltage circuit. This allows for digital signals to be relayed from one circuit to the other without any additional external components or power sources.