4: Theory of operation Series 2600B System SourceMeter® Instrument
4-2 2600BS-901-01 Rev. B / May 2013
Compliance limit principles
A limit acts as a clamp. If the output reaches the limit value, the 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 a limit is reached.
As an example, assume the following:
System SourceMeter
®
instrument: V
SRC
= 10 V; I
LIMIT
= 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 limit 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.
In steady-state conditions, the set compliance limit will restrict the Series 2600B output. This holds
true except for the compliance limit conditions as described in Limits (on page 2-27
) or for fast
transient load conditions.
The Series 2600B can also be set to limit power. This limit can be set in addition to any voltage or
current limits specified. The power limit restricts power by lowering the present limit in effect (voltage
or current) as needed to restrict the SMU from exceeding the specified power limit. The instrument's
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 4-4) topic.
For information on implementing compliance limits, see Setting source and compliance values (on
page 2-22).
Overheating protection
Proper ventilation is required to keep the System SourceMeter
®
instrument from overheating. Even
with proper ventilation, the Series 2600B can overheat if the ambient temperature is too high or the
System SourceMeter
®
instrument is operated as a sink for long periods of time. The System
SourceMeter
®
instrument has an over-temperature protection circuit that will turn the output off if the
instrument overheats. When the over-temperature protection circuit turns the output off, a message
indicating this condition is displayed. You cannot turn the output on until the instrument cools down.
Power equations to avoid overheating
To avoid overheating, do not operate any channel on the instrument in a manner that forces the
instrument to exceed the maximum duty cycle (DC
MAX
), which is computed using the General power
equation (on page 4-3) below. Factors such as the ambient temperature, quadrant of operation, and
high-power pulse levels (if applicable) affect the maximum duty cycle. Exceeding the calculated
maximum duty cycle may cause the temperature protection mechanism to engage. When this
happens, an error message displays and the instrument output is disabled until the internal
temperature of the instrument is reduced to an acceptable level.
You do not have to be concerned about overheating if all of the following are true:
• The instrument is used as a power source and not a power sink.
• The ambient temperature is ≤ 30 °C.
• Extended operating area (EOA) pulsing is not being performed.
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