Keithley 2657A, Reference Manual, Page: 215 / 805

Section 4: Theory of operation Model 2657A High Power System SourceMeter® Instrument Reference Manual
4-14 2657A-901-01 Rev. B/December 2012
Notice that as resistance increases, the slope of the DUT load line increases. As resistance increases
and approaches infinity (open output), the System SourceMeter instrument will source virtually 0 mA
at 1000 V. Conversely, as resistance decreases, the slope of the DUT load line decreases. At zero
resistance (shorted output), the System SourceMeter instrument will source 100 mA at virtually 0 V.
The next figure (labeled "I-source operation in power compliance"), shows what happens if a power
limit of 60 W and a voltage limit of 1000 V is applied to the same 20 k
Ω
load. In I-source mode, power
compliance establishes a second voltage compliance limit, the value of which is determined by
dividing the power compliance limit value by the programmed current source value (for this example,
60 W / 100 mA = 600 V). The instrument will enforce the lower of either the programmed voltage
compliance limit or the power-limited voltage compliance limit. In this example, the System
SourceMeter enforces the power-limited voltage compliance of 600 V and is not able to source its
programmed current (100 mA). For the 20 k
Ω
DUT, the System SourceMeter instrument will only
output 30 mA (at the 600 V limit).
Figure 80: I-source operation in power compliance
V-meter
(V
M
)
500 V
1000 V
Voltage
compliance
limit line
Power
compliance
limit line
Programmed source value:
100 mA
Actual source value:
30 mA
V
V
Programmed current
source value line
100 mA 50 mA
I-source
(I
S
)
Power-limited
voltage compliance
limit line
Operating
point
I
S
= V
M
/ R
= 600 V / 20 k
Ω
= 30 mA
t
2
0
k
Ω
DUT
Loa
d L
in
e
(
R
)
X