Publicité
Les langues disponibles
Les langues disponibles
2 Installation
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 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 created by the low side of the scope probe, which is connected to the load circuit common and
also to the scope's chassis. For this and similar cases, the following steps by order of preference, will
help mitigate common mode current spikes appearing at the output when the power system is turned
on or off by the AC line switch:
1. Install a ferrite core (Keysight p/n 9170-2131) on the power cord to insert additional impedance in
the current path. This ferrite core is now installed inside N6701C and N6702C mainframes.
2. Install a separate bonding wire from the load's common point, to the ground terminal of the power
system. This provides a lower impedance path that helps direct injected currents away from the DC
output leads (and the sensitive load).
3. Break the return path through the external equipment. For example, instead of the single-ended
scope shown in the figure, you can use a differential scope with a floating input or you can connect an
isolated measuring instrument to the load.
Disconnecting the load from the output before switching the power system on or off
will always protect the load from common mode currents.
62
Keysight N6700C Series User's Guide
Publicité
