The input and output of the power circuit are connected to the board through a low-resistance high-power resistor, so that in the case of no soldering resistor, the power circuit can be debugged first, avoiding the influence of the latter circuit.
Generally speaking, the switch controller is a closed-loop system. If the output deteriorates beyond the range that the closed-loop can control, the switching power supply will not work properly. In this case, the feedback and sampling circuits need to be carefully checked. It is important to note that if a large ESR output capacitor is used, a lot of power supply ripple will occur, which will also affect the operation of the switching power supply.