The Fairchild FPF1320 dual-input single-output power switch is a unique IC that switches a load between two power sources. It behaves as a power multiplexer (or mux), using a digital select signal to determine which of the two 1.5 V to 5.5 V input power rails to connect to the output, and can handle a maximum of 1.5 A while blocking unwanted reverse current from flowing from output to input or between inputs. Each input channel is controlled by an internal MOSFET switch, avoiding the voltage drop that occurs when diodes are used to OR multiple power supplies together.
However, the FPF1320 is only available in a tiny 1 mm × 1.5 mm BGA (ball grid array) package, making it difficult for a student or hobbyist to use. To address that issue, this board mounts the chip onto a compact carrier with 0.1″ pin spacing that makes it easy to use with standard solderless breadboards, and it also serves as a breakout for a USB Micro-B connector that can be used to supply one of the input power rails.