FODM121/124/2701/2705 Transistor Optocouplers onsemi FODM121/124/2701/2705 Transistor Output Optocouplers consist of a gallium arsenide infrared emitting diode driving a phototransistor in a compact 4-pin mini-flat package. The lead pitch is 2.54mm. The FODM2705 series consists of two gallium arsenide infrared emitting diodes connected in inverse parallel for AC operation. Typical applications for onsemi FODM121/124/2701/2705 Transistor Output Optocouplers include digital logic inputs, microprocessor inputs, power supply monitor, twisted pair line receiver, and telephone line receiver.