8 - Manual setup
Load Modes
46
SMU4000 Series Instruction Manual
Load Current (LC)
CNFG >
[Source Measure Action] Manual Setup > [Overall] Mode > LC Mode
This is the fundamental operating Load mode of this instrument and has the simplest feedback
loop.
When set to Load Current, the SMU provides rapid measurement of power source regulation
(V/I characteristics). The sensed voltage signal is only used for the meters and protection.
Load current mode is normally used in conjunction with low impedance power supplies and will
be quite stable unless there is significant inductance in either the interconnections or the
source. It is critical to have low inductance connections in this mode.
NOTE
The load cannot be used in constant current mode to test a constant current power supply, as
this combination has only two stable conditions: if the load setting is below the supply limit,
then the supply will not be in constant current operation and will deliver its maximum output
voltage, whereas if the load setting is above the limit of the supply, then the load will saturate at
its minimum operating resistance with the supply delivering its designed current.
The best way to test a constant current supply is to use the instrument in constant resistance
mode.
Load Resistance (LR)
CNFG >
[Source Measure Action] Manual Setup > [Overall] Mode > LR Mode
Load resistance mode simulates a standard resistive load by providing a current drain
proportional to voltage. Unlike fixed resistors or rheostats, the load provides a precisely
controllable resistance with high power dissipation and high temperature stability over a wide
value range.
The current rises as the applied voltage rises at equivalent resistance settings.
When rapidly changing the resistance level setting, the required current is inversely proportional
to the linearly changing resistance value, so the resulting current waveform is very non-linear,
changing rapidly at the low resistance part of the cycle. This rapid change accentuates the effect
of inductance in the interconnecting leads and can easily lead to bottoming and overshoots.
Resistance mode is best used at higher voltages and modest currents.