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86 PRODIGIT
5-5. Constant Voltage mode application
In Constant Voltage (CV) operation the load will attempt to sink as much current as required
in order to reach the set voltage value. CV operation is useful in checking the load
regulation of dc current sources. The CV mode is also ideal for characterizing the current
limit of dc power supplies. These application areas are explained a little more below.
5.5.1
Current source testing.
A common application for a dc current source is as a battery charger. Most battery
chargers are designed to automatically adjust their charging current according to the
battery voltage. In CV mode the electronic load will sink the current that is needed to
reach the desired voltage. The CV mode is therefore ideal for checking the charge
current at a particular voltage level.
If the battery charger is tested at a number of different voltage levels in CV mode a
current curve can be recorded. Thus the battery charger's load regulation can be
checked during development, production and batch testing.
5.5.2
Power supply current limit characterization
The current limit is a necessary function for power supplies. The fold back current
limit curve is very common for fixed output switching power supplies. The constant
current limit curve is more popular for adjustable laboratory power supplies.
It is very difficult or impossible to find the current limit curve by CC or CR mode. However it
becomes simple by using CV mode. The user sets the CV voltage and Records the output
current. Plotting the current measurements against the voltage Settings result in the output
current limit curve of a power supply (Figure 5-6).
INPUT
VOLTAGE
+
-
DC
INPUT
V
CONSTANT VOLTAGE SETTING
Lo
Fig 5-6 Constant Voltage mode application
+
CURRENT
SOURCE
-
ELECTRONIC
CV MODE
V
I
POWER SUPPLY CURRENT
LIMIT TESTING
LOAD
CV SETTING
A
B
C
A
B
C
I
LOAD CURRENT
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