diodeOR

DiodeOR, or diode-OR, is a simple circuit that implements a logical OR function using diodes. In the common positive-logic configuration, each input signal is connected through a diode (anode at the input) to a shared output node, and a pull-down resistor ties the output to ground. When any input is high, its diode conducts and the output rises toward the input voltage minus the diode’s forward drop. If all inputs are low, none conducts and the pull-down resistor holds the output low.

This arrangement is a basic form of diode logic. The output voltage is roughly the maximum of the input voltages minus the forward drop of the conducting diode, so the logic levels are not perfectly rail-to-rail unless diodes with very low forward voltage are used or level shifting is employed. DiodeOR gates can be sensitive to process variations and diode leakage, and they are generally slower and less power-efficient than modern transistor-based logic for high-speed applications. Schottky diodes are often used to reduce forward voltage and improve speed.

A prominent application is power-path management, or supply-rail OR-ing, where multiple supply rails feed a load through diodes. The highest available rail tends to supply the load while lower rails are isolated by their diodes. More broadly, diode-OR is part of historical diode logic used in early digital circuits. For reduced losses in power applications, active or ideal-diode concepts replace the passive diode with MOSFET-based implementations.