Operating Mode Guidelines
CI — Constant Current Mode (Basic Mode)
This mode of operation allows the user to set a fixed current. Three ranges are available. This
set level will not change regardless of changes in the source voltage. Some power sources such
as variable power supplies are rated at a fixed maximum load current and adjustable over a
predetermined voltage range. For example, 5-30V @ 20A. If the resistive load characteristic
were used for this type of a test, it would be necessary to reset the load each time the power
supply voltage was changed in order to maintain desired load current. However, when the load
is in the constant current mode, the current is constant regardless of input voltage fluctuations.
It should be noted that many power supplies are designed for short circuit protection by internal
current limiting and foldback; therefore, the supply may not start up into a constant current load.
Accordingly, it is suggested that the Constant Resistance mode be used as a load when
simulating short circuit protection and recovery of most power supplies, unless otherwise
specified by the manufacturer.
Caution:
The constant current mode should never be used to test a constant current source. The
regulation of the two units will fight for control of the current and an unstable oscillation
will result causing damage to the unit.
CR — Constant Resistance Mode (Basic Mode)
The constant resistance mode regulates the load current in direct proportion to the load voltage.
There are eighteen different resistance ranges available. These are derived from the nine
different voltage and current combinations available, and the two different resistance modes
(HIGH and LOW). The actual resistance values, expressed in Ohms, are outlined in the
specification section of this manual. In general, select the appropriate voltage and current range
for the source, and then determine if the high resistance range or the low resistance range is
required. Other ranges may be selected to tailor the response to a particular application.
EXAMPLE:
Given a 48V source capable of 60A, select the 200V, and 200A ranges. If the high
resistance mode is selected, the maximum current capability is 0.5 Amps/Volt X 48
Volts = 24 Amps MAX. — Too Low!
Select the low resistance mode: 5 Amps/Volt X 48 Volts = 240 Amps MAX. —
sufficient current capability.
The resolution of the load may be improved by selecting the 400V range. This yields:
2.5 Amps/Volt X 48 Volts = 120 Amps MAX. This provides double the resolution, but it
reduces voltage sensitivity.
NOTE:
The resistance may be entered in Ohms or Amps/Volt (1/R). This option is selected
through the front panel menus.
CV — Constant Voltage Mode (Basic Mode)
The constant voltage mode can best be described as a shunt regulator or a zener diode. There
are three voltage ranges available. The load will not conduct any current until the source voltage
tries to exceed the voltage set point. Once the source voltage is high enough the load will shunt
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