law, so only one of the two is an independent variable. The law dictates that the output current I in amps (A) is always
equal to the output voltage V in volts (V) divided by the load resistance R in ohms (Ω):
For example, if the load resistance (R) is such that the current limit (set by knobs 5 and 6) is higher than the voltage
limit (set by knobs 7 and 8) divided by R (i.e., voltage limit is lower than current limit for the load R connected), the
power supply operates in the constant voltage (CV) mode. When in CV mode, the output voltage remains constant
even if the load resistance changes (e.g., if load resistance decreases, the current increases), up to the point when the
preset current limit is reached. The crossover point is reached when the voltage and current limit are reached
simultaneously. Beyond the crossover point, the indicator changes from CV to CC, and the current limit becomes the
lower limit, and the output current remains constant and the output voltage drops in proportion to the further decrease
of the load resistance.
Similarly, crossover from constant current (CC) to constant voltage (CV) mode automatically occurs when the
resistance of the load is increased. A good example of this behavior is charging a 12V lead acid battery. Initially, the
open circuit voltage of the power supply may be set at 13.8V. A discharged battery when connected to the power
supply may demand high charging current beyond the current limit set for the power supply (or the maximum current
capacity of the power supply), and the power supply will operate in constant current mode, with the maximum
charging current equal to the set current limit. As the battery becomes more charged, the voltage will increase, and
eventually reach 13.8V. Beyond that point, the current demand from the battery will drop and fall below the set limit.
