An ideal diode from one MOSFET and two PNPs
Espressif's ESP32-P4X-Function-EV-Board takes power from any of three USB ports. One MOSFET and a dual PNP on each port keep them from pushing current into each other, for a drop of tens of millivolts.
The problem
The ESP32-P4X-Function-EV-Board can be powered from any of its three USB-C ports, and on the schematic all three 5 V lines meet on one rail. Two chargers are almost never at exactly the same voltage, so wired straight together, the higher one pushes current into the lower one.
The fix
A diode in each port would stop it, at the price of about 0.4 V and 400 mW at 1 A. This board does better with four parts per port: a P-channel MOSFET (Q3 for USB0) as the valve, and a dual PNP (Q2) that compares the two sides of it and decides how far to open it. The drop is tens of millivolts, and nothing flows backwards.
The other two ports have the same circuit: Q7 and Q6 on USB1, Q4 and Q5 on USB2.
Redrawn from Espressif's ESP32-P4X-Function-EV-Board schematic, V1.8, 2025-08-05, sheet 6 of 6, 06_SYS_PWR_USB (Q3, Q2, R176, R177, C76). The design is Espressif's; the drawing and the simulation are ours. The board and its design files ↗