2 ORing and power multiplexing techniques

Both ORing and power multiplexing techniques use ideal diodes to connect multiple input power sources to a single output load, but they differ in how they select and switch between different input sources. Figure 1 shows a typical use case for power supply ORing and priority multiplexing.

An ORing circuit facilitates system selection of the best available power source from multiple inputs, based on the highest input voltage. The ideal diodes act as switches that turn on when the input voltage is higher than the output voltage, and turn off when the input voltage is lower than the output voltage. This way, the ORing circuit ensures that the input source with the highest voltage is connected to the output, and prevents reverse current flow and cross conduction between the input sources. If the input power supplies are almost equal, it is possible that both power supplies share the load without any circulating current between them. Thus, reverse current blocking is the primary feature required for realizing an ORing circuit.

A power multiplexing circuit allows the system to switch between different power sources irrespective of the voltage magnitude, based on criteria such as source priority or input voltage availability and magnitude. In this configuration, the control circuit needs to switch power paths between each power supply and load on and off, controlled by its own priority logic or an external signal, such as a microcontroller general-purpose input/output pin. The power multiplexing circuit ensures that only one input source is connected to the output at any point in time, and prevents reverse current flow and cross conduction between the input sources. The circuit in this configuration is therefore required to have both reverse current blocking and load path on and off control features to enable the prioritized power supply to serve the load.