Keysight Technologies N6705C, Operating And Service Manual

Page: 61 / 476

Positive and Negative Voltages
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.
Keysight 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.
Protecting Sensitive Loads from AC Power Switching Transients
This only applies if you are connecting loads that are highly sensitive to voltage or
current transients to the output of the power analyzer. If your load is connected
directly to the output of the power analyzer 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 analyzer.
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 analyzer. Since the AC input has an earth ground, any load that is also earth-
grounded provides a possible return path for common mode currents.
To help mitigate common mode current spikes at the output when the unit is turned on or off:
1. Install a separate bonding wire from the load’s common point, to the ground terminal of the power
analyzer. This provides a lower impedance path that helps direct injected currents away from the DC
output leads (and the sensitive load).
2. Disconnect the load from the output before turning the power analyzer on or off will always protect
the load from common mode currents.
Load Capacitor Response Times
When programming with an external capacitor, voltage response time may be longer than 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 analyzer to briefly
enter constant current or constant power operating mode, which adds additional time.
Keysight N6705C Operating and Service Guide 61
2 Installation