According to various embodiments, an intelligent electronic device IED, such as a protective relay, includes a universal binary input circuit for receiving an AC or DC binary input with a voltage magnitude between approximately 0 Volts and 300 Volts. The universal binary input provides reinforced isolation via an input protection subcircuit and an optocoupler for communicating an optical signal with an electrically isolated controller based on the received binary input signal. In one embodiment, a duty cycle modulation subcircuit generates a pulse width modulated drive signal to drive the optocoupler based on the voltage magnitude of the received binary input. The duty cycle of the pulse width modulated drive signal is (linearly or nonlinearly) inversely proportional to the voltage magnitude of the received binary input.