Keithley 2601B Reference Manual page 234

Section 4: Theory of operation Series 2600B System SourceMeter® Instrument Reference Manual
The first graph in the figure (marked "A: Output characteristics") shows the output characteristics for
the V-source. As shown, the Models 2611B/2612B/2614B/2634B/2635B/2636B can output up to
20.2 V at 1.5 A, or 202 V at 100 mA. Note that when sourcing more than 20.2 V, current is limited to
100 mA.
The second graph in the figure (marked "B: Limit lines") shows the limit lines for the V-source. The
voltage source limit line represents the maximum source value possible for the presently selected
voltage source range. For example, if you are using the 20 V source range, the voltage source limit
line is at 20.2 V. The current compliance limit line represents the actual compliance in effect (see
Limits (on page 2-27)). These limit lines are boundaries that represent the operating limits of the
®
System SourceMeter instrument for this quadrant of operation. The operating point can be anywhere
inside (or on) these limit lines. The limit line boundaries for the other quadrants are similar.
Load considerations (V-source)
®
The boundaries within which the System SourceMeter instrument operates depend on 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.
4-8 2600BS-901-01 Rev. B / May 2013