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4.5 Constant Voltage/Constant Current Characteristic
The working characteristic of this power supply is called a constant voltage/constant
current automatic crossover 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.
shows the relationship between this crossover point and the load.
For example, if the load is such that the power supply is operating in the constant
voltage mode, a regulated output voltage is provided. The output voltage remains
constant as the load decreases, up until the point where the preset current limit is
reached. At that point, the output current becomes constant and the output voltage
drops in proportion to further decreases in load. The crossover point is indicated by
the front panel LED indicators. The crossover point is reached when the CV indicator
goes off and the CC indicator comes on.
Similarly, crossover from the constant current to the constant voltage mode
automatically occurs from an increase in load. A good example of this would be seen
when charging a 12-volt battery. Initially, the open circuit voltage of the power
supply may be preset for 13.8 volts. A low battery will have a low load on the supply
and it will operate in the constant current mode, which may be adjusted for a 1 amp
charging rate. As the battery becomes charged, and its voltage approaches 13.8 volts,
its load increases to the point where it no longer demands the full 1 amp charging
rate. This is the crossover point where the power supply goes into the constant
voltage mode.
Figure 7 - Constant Voltage/Constant Current Characteristic
