KEPCO ATE-DMG SERIES - Manual (Page 36)

3-2 ATE-DMG 042314
however, equally valid for either output side grounded. Care should be taken in measuring the
ripple and noise at the power supply output or at the load, Measuring devices which are a-c line
operated often introduce ripple and noise into the circuit.
In the case where the load must be kept completely off ground (d-c isolated) or it must be oper-
ated above ground potential, grounding can be accomplished by means of a suitable capacitor
connected from either side of the power supply output to the signal ground. The size of the
capacitor should be carefully selected. A value between 0.1 and 1 microfarad has been found to
be successful in many cases.
3.1.3 POWER SUPPLY/LOAD INTERFACE
The general function of a voltage or current stabilized power supply is to deliver the rated output
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 or it may be a considerable distance away. The power
supply designer cannot anticipate every conceivable application, location or nature of the load.
The product must be designed for the widest possible application range and performance spec-
ifications at the output terminals of the power supply. The aim of the following paragraphs is to
aid the user in the final use of the product: The interface of the power supply and the load.
The perfect interface between a power source and its load would mean that the specified perfor-
mance at the output terminals would be transferred without impairment to any load, regardless
of its characteristics, distance from the power supply or environment. To approach this ideal, the
power supply must satisfy certain requirements, interconnecting rules must be closely followed
and Ohm's Law, as well as basic a-c theory must be considered in selecting the interface wiring.
3.1.3.1 LOAD WIRE SELECTION
The stabilized d-c power supply is definitely not an ideal voltage or current source with zero out-
put impedance (VOLTAGE MODE) or infinite output impedance (CURRENT MODE) at all fre-
quencies: All voltage sources have some amount of impedance which increases with frequency
and all current sources have an output impedance which decreases with frequency (refer to Fig-
ure 3-1).
FIGURE 3-1. TYPICAL OUTPUT IMPEDANCE VS. FREQUENCY PLOT FOR STABILIZED D-C SOURCES