Additional Load Considerations - Agilent Technologies Series N6700 User Manual

2 Installation

Additional Load Considerations

Response Time with an External Capacitor
Positive and Negative Voltages
NOTE
Protecting Sensitive Loads from AC Power Switching Transients
NOTE
42
When programming with an external capacitor, voltage response time
may be longer than that for purely resistive loads. Use the following
formula to estimate the additional up-programming response time:
Response Time = (Added Output Capacitor)X(Change in Vout)
(Current Limit Setting)−(Load Current)
Note that programming into an external output capacitor may cause
the power system to briefly enter constant current or constant power
operating mode, which adds additional time to the estimation.
Either positive or negative voltages with respect to ground can be
obtained from the output by grounding (or "commoning") one of the
output terminals. Always use two wires to connect the load to the
output regardless of where or how the system is grounded. The
instrument can be operated with any output terminal ± 240 VDC
including output voltage from ground.
Agilent Models N678xA SMU are optimized for grounding the negative output
terminal. Grounding the positive terminal may result in increased current
measurement noise and a reduction in current measurement accuracy.
This only applies if you are connecting loads that are highly sensitive to voltage
or current transients to the output of the power system. If your load is
connected directly to the output of the power system and is not connected to
chassis ground in any way, you do not need to worry about AC power switching
transients appearing at the output of the power system.
Operating the AC line switch can inject common mode current spikes
into the DC output leads, resulting in voltage spikes that may damage
loads that are highly sensitive to voltage or current transients. Note
that any electronic device meeting international standards for EMI
compliance is likely to generate similar current spikes. This situation
arises from the presence of EMI filters at both the AC input and the
DC output. These filters typically include common mode capacitors
connected to the chassis of the power system. Since the AC input has
an earth ground, any load that is also earth-grounded provides a
possible return path for common mode currents.
The following figure illustrates a typical situation where a load that
might otherwise be floating becomes grounded, thereby providing a
return path for any injected currents. In this case, the return path is
Series N6700 User's Guide