OPERATING INSTRUCTIONS
17
Figure 7. Constant Voltage/Constant Current Characteristic.
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. Fig. 7 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 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 furt her
increases 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 a decrease 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 place a heavy 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 decreases 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.
CONNECTING TWO POWER SUPPLIES IN SERIES
Two Model 1735A power supplies may be connected in series to
provide a variable 0-60 volt output. In this configuration the power
supply can supply up to 3 amps. See Fig. 8 for the connection scheme.
When connected in series, the
VOLTAGE
controls of
each power supply exercise control over a 0-30 volt range.
Add the LED display readings together or connect
external voltmeter across the load to determine the total
output voltage.
Load current may be monitored from either supply; the
readings will be identical since they are connected in
series. Also, since the supplies are connected in series, it is
only necessary to set the current limit on one of the
supplies; the other may be set for maximum.
