Efficiency

The efficiency of a power supply is simply the ratio of its total output power to its total input power. To obtain the true input power (rms voltage x in-phase rms current) of a typical AC-to-DC converting power supply, commercially available wattmeters or AC sources can be used to measure the necessary parameters. The instrument used to measure the input current and voltage must be capable of sampling the input signals at a rate fast enough to produce accurate measurements.

This test serves as a good indication of the overall correct operation of the power supply under test. If the measured efficiency is outside the specified range for the topology of the power supply, it is probable that a design flaw or a manufacturing problem exists that should be addressed.

Test Overview/Procedures

The efficiency and power factor of the power supply under test should be measured under steady-state operation after the unit has been allowed to warm up. The electronic load can be operated in CC mode (for CV power supplies) and CV mode for (CC power supplies). At least two load settings should be used, one of them being the maximum rated load for the power supply under test (see Figure 9 for test con- figuration). Some power supplies vary substantially in efficiency and power factor as a function of load- ing. In this case, the load should be varied through enough settings so that curves can be plotted from the data to provide the best representation of the test results.

Start-Up

The start-up delay of a power supply is the amount of time between the application of AC input and the time at which the outputs are within their reg- ulation specification. For switching power supplies or power supplies with current limiting, this time period is essential for proper sequencing of the out- put voltage at turn-on. In switching power supply designs, undesirable events can occur at turn-on, causing current spikes which can destroy the switch- ing transistors. The problem occurs when the feed- back loop tries to compensate for the low output voltage that it sees when the AC input is initially applied to the power supply. This problem is usually solved by adding “soft-start” circuitry to limit the time the switching transistors are turned on during the start-up sequence. This will limit the current flow through them until the power supply has reached stable operation.

Another undesirable condition that can occur during power supply start-up is voltage latch-up. In this case, the output voltage of a CV power sup- ply with current foldback fails to reach its full value at turn-on because the output current attempts to immediately go to a high value. The protective response of the current foldback circuitry of the power supply can cause the output voltage to “latch- up” at a point where the current that must be dis- sipated can cause damage to the power supply (see Figure 10). It is, therefore, beneficial to measure the start-up delay time and fully characterize it to ensure safe operation at turn-on.

Figure 9. Configuration for Testing Efficiency and Power Factor

In this test configuration for measuring power supply efficiency and power factor, the variable AC source provides measurements for input power and power factor.

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Agilent Technologies AN 372-1 specifications Efficiency, Start-Up
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AN 372-1 specifications

Agilent Technologies AN 372-1 is a versatile and highly regarded instrument in the field of electronic testing and measurement. Designed primarily for research and development, as well as validation in production environments, this advanced technology showcases Agilent's commitment to providing high-quality measurement solutions.

One of the standout features of the AN 372-1 is its wide frequency range capability, enabling it to effectively measure signals across various applications. This instrument supports a frequency range extending up to 26.5 GHz, making it suitable for high-frequency applications in telecommunications, aerospace, and defense sectors. With this broad frequency capability, users can rely on the AN 372-1 for accurate and reliable measurements in the most demanding environments.

Another significant attribute of the AN 372-1 is its high dynamic range, which allows for precise detection of both weak and strong signals in the presence of noise. This characteristic is essential for engineers working to ensure signal integrity in complex systems, as it allows for the identification of issues that may otherwise go unnoticed. Coupled with a fast sweep speed, the device can quickly capture transient events or changes in signals, making it a vital tool for time-sensitive applications.

The user interface of the AN 372-1 is designed for ease of use, with a touchscreen display that simplifies interaction and data visualization. Its intuitive design enables users to set up measurements and navigate through the many options effortlessly. Furthermore, the instrument is equipped with advanced analysis features and software that enhance data interpretation and manipulation, allowing engineers to derive meaningful insights from their measurements quickly.

In addition to its measurement capabilities, the AN 372-1 supports advanced connectivity options, including USB, LAN, and GPIB. This ensures seamless integration with other instruments and systems, facilitating a more streamlined testing workflow. The ability to connect with external software also enhances its functionality, allowing users to automate processes and improve test efficiency.

The AN 372-1's rugged design ensures it can withstand the challenges of both laboratory and field use. Its build quality speaks to Agilent's commitment to creating long-lasting instruments that offer reliable performance throughout their lifecycle. Overall, the Agilent Technologies AN 372-1 stands out as a comprehensive tool for engineers and researchers requiring precise, reliable, and efficient electronic measurements across a myriad of applications.
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