Constant current charging is a way to charge common batteries. This is a charging method where batteries are charged with a constant current from beginning to end.
A standard switching power supply (hereunder “power supply”), on the other hand, is a constant voltage power supply so it monitors fluctuations in output voltages, inputs the results in the control circuit, and executes constant voltage controlling (feedback controlling).
The output voltage is therefore maintained constant but the output current fluctuates depending on load conditions so it cannot be used as is for battery charging that requires a constant current (constant current controlling).
The overcurrent protection function of the power supply is to therefore be used. The overcurrent protection function was originally designed to suppress current values and avoid deterioration and damage to the power supply when it overloads and a current exceeding the rating flows. The suppressing of the current values is diverted and the suppressed current is used as a constant charging current for the battery.
It is important to keep in mind here that there are some characteristics of overcurrent protection that make it inappropriate for charging batteries.