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6 Advanced Source and Measurement Functions
Power Limit Operation
156
You can specify if the delay timer is started by any transition of the
output into CC mode (select CC Transition), or if the delay timer is
started at the end of a settings change in voltage, current, or output
state (select Settings Change).
Factors that influence how long the settings change or output load
change may last include: difference between old output value and
new output value, the current limit setting, and the load capacitance
in CV mode or load inductance in CC mode. The delay required must
be determined empirically; the power module programming-response
time characteristics may be used as guidelines.
Also, the time it takes the output to go into CC mode varies -
depending on the magnitude of the over-current condition compared
to the current limit setting. For example, if the over-current is only
slightly greater than the current limit setting, it may take several tens
of milliseconds, depending on the power module type, for the output
to set the CC status bit. If the over-current is significantly greater
than the current limit setting, it may only take a few milliseconds or
less, depending on power module type, for the output to set the CC
status bit. To determine when the output will shut down, you must
add the time it takes to set the CC status bit to the over-current
protection delay time. If the over-current persists beyond the sum of
these two time intervals, the output will shut down.
For Agilent N6705 mainframes, the instrument will operate
normally as long as the combined output power is within the power
rating of the mainframe If the combined power drawn from all of the
outputs exceeds the mainframe's power rating of 600 W, a power
fault protection event will occur. This causes ALL outputs to turn off
and remain off until a protection clear command is given. A status bit
(PF) will indicate that a power fault protection event has occurred.
For Agilent N678xA SMU, the power limit function does not apply
because their maximum output power is rated at 20W.
For Agilent N675xA, and N676xA power modules, the power limit
function limits the output power at its programmed setting. A status
bit (CP+) will indicate that the output is in power limit mode. When
the power drawn by the load is reduced below the power limit
setting, the output returns to normal operation. Note that these
power modules contain an active down-programmer circuit, which is
limited to about 7 W continuous power. A status bit (CP-) will
indicate that the output has reached the negative limit.
Model N6705 User's Guide
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