How to measure switching power supply with digital oscilloscope
Power supplies come in a wide variety of types and sizes, from traditional analog power supplies to high-efficiency switching power supplies. They all face complex and dynamic work environments. Equipment loads and demands can change significantly in an instant. Even "everyday" switching power supplies must be able to withstand instantaneous peaks that far exceed their average operating levels. Engineers designing power supplies or systems that will use power supplies need to understand how the power supply operates under static conditions as well as under worst-case conditions.
In the past, characterizing the behavior of a power supply meant measuring quiescent current and voltage with a digital multimeter and performing painstaking calculations with a calculator or PC. Today, most engineers turn to oscilloscopes as their preferred power measurement platform. Modern oscilloscopes can be equipped with integrated power measurement and analysis software, simplifying setup and making dynamic measurements easier. Users can customize key parameters, automate calculations, and see results in seconds, not just raw data.
Power supply design issues and their measurement requirements
Ideally, every power supply should behave like the mathematical model for which it was designed. But in the real world, components are defective, loads can change, power supplies can distort, and environmental changes can alter performance. Moreover, changing performance and cost requirements also make power supply design more complex. Consider these questions:
How many watts of power can the power supply sustain beyond its rated power? How long can it last? How much heat does a power supply dissipate? What happens when it overheats? How much cooling airflow does it require? What happens when the load current increases significantly? Can the device maintain rated output voltage? How does the power supply respond to a complete short circuit at the output? What happens when the input voltage of the power supply changes?
Designers need to develop power supplies that take up less space, reduce heat, reduce manufacturing costs, and meet stricter EMI/EMC standards. Only a rigorous measurement system can enable engineers to achieve these goals.
