Keithley 2651A Reference Manual page 208

Model 2651A High Power System SourceMeter® Instrument Reference Manual
Load considerations (V-source)
The boundaries within which the High Power System SourceMeter
the load (device-under-test (DUT)) that is connected to the output. The following figure shows
operation examples for resistive loads that are 2 kΩ and 800 Ω, respectively. For these examples, the
System SourceMeter instrument is programmed to source 10 V and limit current (10 mA). In addition,
for A: Normal V-source operation and C: V-source operation in power compliance the System
SourceMeter instrument is programmed to limit power (60 mW).
In the following figures first graph (labeled "A: Normal V-source operation"), the System SourceMeter
instrument is sourcing 10 V to the 2 kΩ load and subsequently measures 5 mA. As shown, the load
line for 2 kΩ intersects the 10 V voltage source line at 5 mA. The current compliance limit and the
power compliance limit are not reached (the instrument is not limited through its compliance settings).
The second graph in the figure (labeled "B: V-source operation in current compliance"), shows what
happens if the resistance of the load is decreased to 800 Ω. The DUT load line for 800 Ω intersects
the current compliance limit line placing the System SourceMeter instrument in compliance. When in
compliance, the System SourceMeter instrument will not be able to source its programmed voltage
(10 V). For the 800 Ω DUT, the System SourceMeter instrument will only output 8 V (at the 10 mA
limit).
Notice that as resistance decreases, the slope of the DUT load line increases. As resistance
approaches infinity (open output), the System SourceMeter instrument will source virtually 10 V at
0 mA. Conversely, as resistance increases, the slope of the DUT load line decreases. At zero
resistance (shorted output), the System SourceMeter instrument will source virtually 0 V at 10 mA.
The third graph in the figure (labeled "C: V-source operation in power compliance"), shows what
happens if a power limit of 60 mW is applied. As the instrument attempts to output the programmed
source value of 10 V, the power compliance limit line is reached placing the System SourceMeter
instrument in power compliance. The System SourceMeter instrument enforces the power compliance
limit by setting the current compliance limit line to the new power limited current compliance limit line
setting (which in this case is 6 mA). In compliance, the System SourceMeter instrument will not be
able to source its programmed voltage (10 V). For the 800 Ω DUT, the System SourceMeter
instrument will only output 4.8 V (at the 5 mA limit). In this example, current will never exceed the
programmed compliance of 10 mA, or the programmed power compliance of 60 mW, under any load.
2651A-901-01 Rev. A / March 2011
Section 4: Theory of operation
®
Instrument operates depend on
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