The IL1/ IL2/ IL5 are optically coupled isolated pairs employing GaAs infrared LEDs and silicon NPN phototransistor. Signal information, including a DC level, can be transmitted by the drive while maintaining a high degree of electrical isolation between input and output. The IL1/ IL2/ IL5 are especially designed for driving medium-speed logic and can be used to eliminate troublesome ground loop and noise problems These couplers can be used also to replace relays and transformers in many digital interface applications such as CRT modulation.