Oscilloscope: A Power Measurement Tool

Power supply refers to a subsystem, component or system that transforms electrical power from a particular form to another, usually converting alternating current (AC) to direct current (DC) power. It has to be noted that the proper operation of electronic equipment, which range from personal computers to industrial machinery and military equipment, relies on the reliability and performance of DC power supplies.

Oscilloscope’s power supplies come in various kinds and sizes, from conventional analog types to highly-efficient switch-mode power supplies, with each of them facing a complex, dynamic operating environment. Device demands and loads can significantly change from one instant to the other. A commodity switch-mode power supply has to survive sudden peaks, exceeding its average operating levels.

Characterizing a power supply’s behavior means taking voltage measurements and static current with a digital multimeter and painstakingly making calculations on a PC or a calculator. However, most engineers nowadays consider oscilloscope as one of the preferred power measurement platform. Equipped with integrated analysis and power measurement software, the oscilloscope simplifies set up, making it easier for users to take measurements over time. The oscilloscope even allows users to automate calculations, customize critical parameters and view results.

Ideally the behavior of every power supply is similar to the mathematical model employed to design it. However, in reality, loads vary; components are not perfect; changes in the environment affect performance and line power could be distorted.

Thus, designers are required to create a power supply that occupies less space, meets tougher EMC/EMI standards, cuts manufacturing costs and reduces heat. Engineers can achieve these goals by using a rigorous regime of measurements.

With their relatively low frequencies, power measurements may appear simple to users used to taking high-bandwidth measurements using an oscilloscope. On the contrary, power measurement present users with a plethora of challenges that has never been confronted by a high-speed circuit designer. The voltage on a switching device can be rather huge, and could be “floating”, which means that it is not referenced to the ground. Variations could be observed in the signal’s period, pulse width, duty cycle and frequency. Waveforms should be faithfully captured as well as analyzed for imperfections.

The demands presented on the oscilloscope are exacting, with various probe types single-ended, current and differential required simultaneously. The device should have a deep memory in order that it can deliver the record length required by long, low-frequency acquisitions. It may even be required to capture signals of widely different scales in a single acquisition.

When preparing the oscilloscope for power measurements, users should ensure that it offers the basic sample rate and bandwidth required to handle the switching frequencies across a Switch-mode power supply (SMPS). Power measurements demands at least two channels, one for current and one for voltage. Users should also note that the facilities used to take power measurements are easy to operate and are reliable. Users should also have accurate voltage and dependable current probes, in order that they can align differing delays expediently.