Abstract: An LED input emulator to interface a signal source designed for use with an LED optocoupler, to capacitive or other galvanic isolation circuitry, emulating LED forward and reverse bias voltages. VR reverse blocking circuitry includes MP1 and MP2 PMOS transistors coupled to an emulator anode port, and to emulate LED reverse bias voltage. VF control circuitry includes a variable resistance (MP3) coupled between anode and cathode ports, and a current control circuit coupled to an output node, and to control current through the variable resistance to maintain a desired forward voltage at the output node. In an example embodiment, the VF control circuitry is implemented with an amplifier and a bandgap voltage reference circuit coupled to the output node, generating both reference and feedback voltages input to the amplifier to control the variable resistance.

Abstract: An apparatus comprising an Opto-coupler using LED and photo transistor as a basis for the isolation is provided. An Input of the opto-coupler based isolator is an LED. The opto-coupler uses PMOS MP1 and MP2 which act as reverse blocking diode, and thus providing ?5V reverse bias breakdown voltage. Moreover, PMOS MP1 and MP2 act as switch for the forward input current and provides a conductive path between the ANODE and Supply node.