B&K Precision 1671A - Manual - Manual (Page 15)

9
OPERATING INSTRUCTIONS
7. If the load current reaches the constant current value, the
CURRENT LIMITED indicator will light. If the load current
drops below the constant current value, the CURRENT
LIMITED indicator will go off. In this case the power supply
automatically switches to the constant voltage mode, and further
rotation of the CURRENT control will not increase the output
current.
Constant Voltage/Constant Current Characteristic
The working characteristic of the variable 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 lead change. The intersection of constant voltage and
constant current modes is called the crossover point. Fig 3 shows the
relations ship between this crossover points 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 lad increases, 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
increases in load. The crossover point is indicated by the front panel
CURRENT LIMITED indicator lighting.
Similarly, crossover from the constant current to the constant voltage
mode automatically occurs from a decrease in load. A good example of
this would be seen when charging a 12-volt car battery. Initially, the open
circuit voltage of the power supply may be preset for b 13.8 volts. A low
battery will place a heavy load on the power supply and it will operate in
the constant current mode, which may be adjusted of a 2 Amp charging
rate. AS the battery becomes charged, and its voltage approaches 13.8
volts, its load decreased to the point where it no longer demands the full 2
Amp charging rate. This is the crossover point where the power supply
goes into the constant voltage mode.
12 VDC Output
The 12 Vdc is a fixed voltage supply providing up to 500 mA (0.5
amp) continuous. The 12 Vdc output is available at the two left OUTPUT
12V tie points. Be sure to observe polarity.
Figure 3. Constant Voltage/Current Characteristics