U1882B Measurement Application for Infiniium Oscilloscopes

Fast, Automatic and Reliable Characterization of Switching Mode Power Devices

Today’s power supply designers are facing an increasing number of constraints in the development of high-efficiency, low-cost power supplies. Cost-effective solutions used to be the designer’s key target. Today, rising energy costs bring power supply efficiency to the forefront. Additionally, other constraints such as design compactness, migration to digital control, tighter voltage tolerances, and regulations for power quality and EMI force the need for quick and reliable power supply testing. Increasing design constraints translate into more time dedicated to power device measurement and analysis for today’s power supply designers.

In spite of the increasing analysis capability offered by many oscilloscopes over recent years, it is not uncommon to see designers perform measurements and characterization manually. These measurements typically take a considerable amount of time to capture, analyze, and report.

Full-featured Measurements and Automatic Reporting of Switching Mode Power Supply (SMPS) Characteristics

Now you can skip the time‑consuming manual measurements when you are characterizing your power devices. The U1882A power measurement application for Keysight Technologies, Inc. oscilloscopes provide a full suite of power measurements that run directly on an Infiniium S-Series and 9000 Series oscilloscope. Keysight’s power measurement application offers seven modules to help you characterize your devices (power device analysis, input line analysis, output analysis, turn on/off analysis, transient analysis, modulation analysis) in addition to deskew and report generation. Each module contains relevant measurement and setup selections for easy repeatability.

Auto Deskewing and U1880A Deskew Fixture

A power measurement is simply a point-by-point multiplication of the voltage and current waveforms measured by the voltage and current probes. To make accurate power measurement and calculation, it is extremely important to equalize the time delay between the voltage and current probes using a procedure known as deskewing. This step is critically important since a small offset in the timing of the voltage and current traces can cause a large error in the instantaneous power reading. To deskew a pair of probes, drive both voltage and current probes with the same pulse signal using the U1880A deskew fixture. With only a single click on the menu, deskewing is automatically performed and its values are saved in the power measurement software, so the next time you launch the power measurement application, you can use the saved deskew values or perform the deskewing again.

The deskew accuracy is a function of the electrical characteristics of the voltage and current probes as well as the risetime of the signal under test. In general, higher bandwidth probes will allow for better risetime fidelity and better deskew resolution. Keysight's N2790A to N2793A differential probes are recommended for most applications.

The U1880A deskew fixture is recommended for use with the following voltage and current probe combinations given various test signal risetime characteristics.

Power Device Analysis

The switching loss in a power supply determines its efficiency. You can easily characterize instantaneous power loss and conduction power loss at the switching device over a designated switching cycle. The dynamic ON resistance measurement shows you power loss while the power transistor is conducting.

To determine the reliability of the power supply it is very important to measure the power loss during dynamic load changes and to observe the SOA (safe operating area) plot. Using deep acquisition memory on the scope with the SOA plot, you can easily identify improper power transistor behavior.