A DC power supply is to supply voltage and current in constant voltage (CV) or constant current (CC) mode within the rated output range. Such working characteristics is called a constant voltage/constant current automatic cross-over type. This permits continuous transition from constant current to constant voltage modes in response to the load change. The intersection of constant voltage and constant current modes is called the crossover point. Below figure shows the relationship between this crossover point and the load.

In CV mode, a regulated output voltage is provided. The output voltage remains constant as the load increases while the output current changes in response to the load changes, up till the present current limit point is reached. At that point, the output current becomes constant and the output voltage drops in proportion to the further increases in load.
Similarly, in CC mode, crossover from the CC to CV mode automatically occurs from a decrease in the load. A regulated output current is provided. The output current remains constant as the load decreases while the output voltage changes in response to the load changes.
A power supply with CV and CC operation mode can be operated in only one mode according to load situation. The power supply is in CV mode when the actual load is over the preset load capacity; and the power supply is in CC mode when the actual load is below the preset load capacity.