Agilent Technologies AN 372-1 specifications Introduction, An Overview of Power Supply Topologies

Introduction

As regulated-power supply technology evolves, testing methods for design verification and product function require more sophisticated electronic equip- ment. The different power supply architectures and output combinations also dictate the need for versatile test instruments that can accommodate a broad range of specifications. As a result, one test- ing requirement that has been growing in impor- tance is the method of loading the power supply under test. The need for a higher degree of load control due to test sophistication, such as the need for computer programmability, has increased the demand for electronic load instruments. The follow- ing examination of the most common power supply architectures or topologies clearly illustrates the growing need for higher performance and versatility in electronic loads and power supply test equipment.

An Overview of Power Supply Topologies

Of all the possible power supply topologies, linear and switching regulation techniques are the most common design implementations. Linear power supplies are typically used in R&D environments and in production test systems because they pro- vide high performance, low PARD (ripple and noise), excellent line and load regulation, and superior transient recovery time specifications. However,

they are relatively inefficient when compared to switching power supplies, and tend to be large and heavy due to the heat sinks required to contin- uously dissipate power from the series transistors and due to the magnetics used in this design. Typi- cally, linear power supplies provide a most effec- tive solution in lower power applications, and are often used as subassemblies in various products.

Switching power supplies address the disadvan- tages of linear power supplies (namely the low effi- ciency and relatively large size and weight), and are therefore a more effective and less costly solu- tion for high power applications. The relative dis- advantages occur in three areas when compared to linear power supplies: slower transient recovery time, higher PARD, and lower reliability. Switching power supplies are used in a wide variety of indus- tries and environments, and are commonly found as subassemblies in products such as computers, computer peripherals, and copiers. Recent power supply designs combine the best features of switch- ing and linear topologies. Below, Table 1 compares the typical specifications for linear and switching topologies.

Table 1

Regulation	Load	Line	Transient
Technique	Regulation	Regulation	Response	PARD	Efficiency
Switching	0.05 – 0.5%	0.05 – 0.5%	1 – 20 ms	5 – 20 mVrms	65 – 85%
				20 – 150 mVp-p
Linear	0.005 – 0.1%	0.005 – 0.1%	20 – 200 µs	0.25 – 5 mVrms	30 – 50%
(Series Pass)				1.0 – 15 mVp-p

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