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Agilent AN 372-1
Power Supply Testing
Application Note
An electronic load offers a broad
range of operating modes, providing
versatile loading configurations
needed for characterizing and
verifying dc power supply design
specifications.
Load
I
Time
T1 Abrupt Load Change
Standard
Output
Quantity
Load Effect
Load Overshoot Amplitude
Effect
Rand
Load Effect
Load Effect Load Effect
I Transient Settling
Recovery Time
Time Load Settling Effect
Time
T1
Agilent Technologies
Introduction
As regulated-power supply An Overview of Switching power supplies
technology evolves, testing Power Supply Topologies address the disadvantages of
methods for design verification Of all the possible power linear power supplies (namely
and product function require supply topologies, linear and the low efficiency and relative-
more sophisticated electronic switching regulation tech- ly large size and weight), and
equipment. The different power niques are the most common are therefore a more effective
supply architectures and out- design implementations. Linear and less costly solution for
put combinations also dictate power supplies are typically high power applications. The
the need for versatile test used in R&D environments relative disadvantages occur in
instruments that can accommo- and in production test systems three areas when compared to
date a broad range of specifica- because they provide high linear power supplies: slower
tions. As a result, one testing performance, low PARD (ripple transient recovery time, higher
requirement that has been and noise), excellent line and PARD, and lower reliability.
growing in importance is the load regulation, and superior Switching power supplies are
method of loading the power transient recovery time specifi- used in a wide variety of indus-
supply under test. The need for cations. However, they are tries and environments, and
a higher degree of load control relatively inefficient when are commonly found as sub-
due to test sophistication, such compared to switching power assemblies in products such as
as the need for computer pro- supplies, and tend to be large computers, computer peripher-
grammability, has increased and heavy due to the heat als, and copiers. Recent power
the demand for electronic load sinks required to continuously supply designs combine the
instruments. The following dissipate power from the series best features of switching and
examination of the most com- transistors and due to the linear topologies.
mon power supply architec- magnetics used in this design.
tures or topologies clearly Typically, linear power sup- Below, Table 1 compares the
illustrates the growing need for plies provide a most effective typical specifications for linear
higher performance and versa- solution in lower power appli- and switching topologies.
tility in electronic loads and cations, and are often used
power supply test equipment. as subassemblies in various
products.
Table 1
Regulation Load Line Transient PARD Efficiency
Technique Regulation Regulation Response
Switching 0.05