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One of the most important considerations in establishing a successful grounding scheme is to
avoid GROUND LOOPS. Ground loops are created when two or more points are grounded at
different physical locations along the output circuit. Due to the interconnection impedance
between the separated grounding points, a difference voltage and resultant current flow is
superimposed on the load. The effect of this ground loop can be anything from an undesirable
increase in output noise to disruption of power supply and/or load operation. The only way to
avoid ground loops is to ensure that the entire output/load circuit is fully isolated from ground,
and only then establish a single point along the output/load circuit as the single-wire ground
point.
The exact location of the "best" d-c ground point is entirely dependent upon the specific applica-
tion, and its selection requires a combination of analysis, good judgement and some amount of
empirical testing. If there is a choice in selecting either the OUTPUT or COMMON output termi-
nals of the power supply for the d-c ground point, both sides should be tried, and preference
given to the ground point producing the least noise. For single, isolated loads the d-c ground
point is often best located directly at one of the output terminals of the power supply; when
remote error sensing is employed, d-c ground may be established at the point of sense lead
attachment. In the specific case of an internally-grounded load, the d-c ground point is automat-
ically established at the load.
The output and common terminals of BOP power supplies are d-c isolated ("floating") from the
chassis in order to permit the user maximum flexibility in selecting the best single point ground
location. Care must be taken in measuring the ripple and noise at the power supply: measuring
devices which are a-c line operated can often introduce additional ripple and noise into the cir-
cuit.
There is, unfortunately, no "best" method for interconnecting the load and power supply. Individ-
ual applications, location and nature of the load require careful analysis in each case. Ground-
ing a single point in the output circuit can be of great importance. It is hoped that the preceding
paragraphs will be of some assistance in most cases. For help in special applications or difficult
problems, consult directly with Kepco's Application Engineering Department.
2.5.3.1
GROUNDING NETWORK CONFIGURATION
When the output is floating there is a tendency for large changes in output voltage to affect the
digital programming section, possibly resulting in an erroneous output. Decoupling capacitors
from each of the two output terminals to the chassis via a terminal block link form a grounding
network. The grounding network is designed to reduce high frequency noise and ensure that the
digital programming section is not adversely affected by the dynamic swing of the output. The
power supply is shipped with the grounding network connected: a connection between terminals
TB1-4 (GND NET) and TB1-5 (GND). To disconnect the grounding network from the output,
remove the connection across TB1-4 and TB1-5.
2.5.4
POWER SUPPLY/LOAD INTERFACE
The general function of a voltage- or current-stabilized power supply is to deliver the rated out-
put quantities to the connected load. The load may have any conceivable characteristic: it may
be fixed or variable, it may have predominantly resistive, capacitive or inductive parameters; it
may be located very close to the power supply output terminals or it may be a considerable dis-
tance away. The perfect interface between a power supply and its load would mean that the
specified performance at the output terminals would be transferred without impairment to any
load, regardless of electrical characteristics or proximity to each other.
BOP HIPWR 080709
2-9
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