Keithley 4200-SCS Reference Manual page 60

Section 3: Source-Measure Hardware
V-Source operation examples
Figure 3-9
For these examples, the SMU is programmed to source 50 V and limit 5 mA. In
SMU is sourcing 50 V to the 20 k Ω load and subsequently measures 2.5 mA, which is well within
the 5 mA programmed current limit. As shown, the load line for 20 k Ω intersects the 50 V voltage
source line at 2.5 mA.
3-9B shows what happens if the resistance of the load is decreased to 8k Ω. The DUT load
Figure
line for 8k Ω intersects the current compliance limit line placing the SMU in compliance. In
compliance, the SMU will not be able to source its programmed voltage (50 V). For the 8k Ω DUT,
the SMU will only output 40 V (at the 5 mA limit).
Notice that as resistance decreases, the slope of the DUT load line increases. As resistance
approaches infinity (open output), the SMU will source virtually 50 V at 0 mA. Conversely, as
resistance decreases, the slope of the DUT load line increases. At zero resistance (shorted
output), the SMU will source virtually 0 V at 5 mA.
Regardless of the load, current will never exceed the programmed compliance of 5 mA.
Figure 3-9
V-Source operating examples
A. Normal V-source operation
I M = V S / R
B. V-Source in compliance
V S = I M R
3-10
shows operation examples for resistive loads that are 20 k Ω and 8k Ω, respectively.
5mA
I-Meter
(I M )
2.5mA
= 50V/20kΩ
= 2.5mA
5mA
I-Meter
(I M )
.
= (5mA) (8kΩ)
= 40V
Return to
Current Limit
Load Line
50V
V-Source (V S )
Current Limit
Operating
Load Line
Point
40V 50V
V-Source (V S )
Section Topics
Model 4200-SCS Reference Manual
Figure
Operating
Point
Voltage Source
Load Line
Voltage Source
Load Line
4200-901-01 Rev. S / May 2017
3-9A, the