Section 4: Theory of operation Model 2651A High Power System SourceMeter® Instrument Reference Manual
4-2 2651A-901-01 Rev. A / March 2011
Source-measure concepts
Overview
This section provides detailed information about source-measure concepts, including:
• Compliance principles (on page 4-2)
• Overheating protection (on page 4-3)
• Operating boundaries (on page 4-5)
• Basic circuit configurations (on page 4-14)
• Guard (on page 4-17)
Compliance principles
Compliance acts as a clamp. If the output reaches the compliance value, the High Power System
SourceMeter
®
Instrument attempts to prevent the output from exceeding that value. This action
implies that the source will switch from a V-source to an I-source (or from an I-source to a V-source)
when in compliance.
As an example, assume the following:
System SourceMeter
®
instrument: V
SRC
= 10 V; I
CMPL
= 10 mA
Device under test (DUT) resistance: 10 Ω
With a source voltage of 10 V and a DUT resistance of 10 Ω, the current through the DUT should be:
10 V / 10 Ω = 1 A. However, because the compliance is set to 10 mA, the current will not exceed that
value, and the voltage across the resistance is limited to 100 mV. In effect, the 10 V voltage source is
transformed into a 10 mA current source.
The Model 2651A output does not exceed the compliance limit, except for the compliance limit
conditions described in Source-measure capabilities
(on page 2-11).
The Model 2651A can also be set to limit power. This limit can be set in addition to any voltage or
current compliance limits specified. The instrument's compliance limit operation changes dependent
on the source mode (current or voltage), load, and the configured limits (current, voltage, and power).
For additional details on using limits, including load considerations when specifying both a current (or
a voltage) limit and a power limit, see the Operating boundaries
(on page 4-5) topic.
For information on implementing compliance limits, see Compliance limit
(on page 2-12).
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