Constant Resistance Mode Application; Fig 5-4 Constant Resistance Mode Application - Prodigit 3270 Series Operation Manual

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5-4. Constant Resistance mode application

Operating in Constant Resistance mode is useful for testing both voltage and current
sources. The CR mode is particularly suited for the 'soft start' of power supplies.
This is explained in more detail below.
5.4.1 Power supply power up sequence
In constant current mode the demand at initial 'Load ON' of the preset current value
is almost instantaneous. This might cause the Device under Test (DUT) problems
meeting the relatively high current demand at initial switch on. .
For example: A 5V/50A output power supply may not be able to deliver 50A over its
entire start-up range of 0-5 volts. In many cases the power supply's short circuit or
over current protection circuit cause the power supply to shut down. This is because
the power supply is trying to deliver the 50A at a voltage level that is too low.
The answer to this problem is not to use CC mode but to use CR mode instead.
This is because in CR mode the current and voltage ramp up together providing a
'soft start' when compared to standard CC mode.
However please note that with the 3270 series of Electronic Loads allow an
adjustable current ramp can be set. This feature is found within the dynamic settings
as RISE slew rate. Even in static mode the 3270 series load will regulate its current
demand at 'Load ON' in line with the adjusted RISE slew rate. The FALL slew rate
also in the dynamic settings allows the current ramp down to be controlled at 'Load
OFF'.
+
CURRENT
SOURCE
-
ELECTRONIC LOLAD
CR MODE
V
INPUT
VOLTAGE
LOAD RESISTANCE
SETTING
LOAD CURRENT

Fig 5-4 Constant Resistance mode Application

VOLTAGE
SOURCE
ELECTRONIC LOLAD
CR MODE
- +
DC
OUTPUT
I