Because there is a capacitor at the main power 5V, the voltage drop at point A cannot be completed instantaneously, causing the MOS tube to be turned on in time, the main and backup power of the circuit cannot be switched without gaps, and the following devices will restart.
Thomas ポストする July 31, 2020
If there is no capacitor, the switch can be switched without gaps and the voltage does not drop. However, generally there are capacitors, which cannot make the voltage at point A drop quickly. The voltage drop at point A is shown in the figure, and it drops to 1.76V (3.76V battery voltage drop It takes 364 milliseconds to go to the turn-on voltage of 2V, and all the subsequent MCUs restarted.
Tyler ポストする July 31, 2020
The voltage needs another 20 milliseconds to complete the gapless switching. It is possible to remove the capacitor, but the capacitor is originally used for filtering.
Jayden ポストする July 31, 2020
I have also encountered this kind of problem. The easiest way is to increase the cost and add a voltage comparator to control the gate of the MOS.
