A power supply is a component, subsystem, or system that converts electrical power from one form to another; commonly from alternating current (AC) utility power to direct current (DC) power. The proper operation of electronic devices ranging from personal computers to military equipment and industrial machinery depends on the performance and reliability of power supplies.

There are many different kinds and sizes of power supplies from traditional linear types to high-efficiency switch-mode power supplies. All face a complex, dynamic operating environment. Device loads and demands can change dramatically from one instant to the next. Even a commodity switch-mode power supply must be able to survive sudden peaks that far exceed its average operating levels. Engineers designing power supply's or the systems that use them need to understand their supplies behavior under conditions ranging from quiescent to worst-case.

Historically, characterizing the behavior of a bench power supply has meant taking static current and voltage measurements with a digital multimeter and performing painstaking calculations on a calculator or PC. Today most engineers turn to oscilloscopes for characterization and troubleshooting during design, and purpose-built power analyzers for system-level validation and compliance testing.

Modern oscilloscopes can be equipped with integrated power measurement and analysis software which simplifies setup and makes it easier to conduct measurements over time. Users can customize critical parameters, automate calculations, and see results, not just raw numbers, in seconds.

This primer will focus on switch-mode power supply design measurements with an oscilloscope and application-specific software. It will also introduce power analyzers, in the context of power quality testing.

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