How to Benchmark AC/DC Power Supplies Using Programmable Electronic Loads

By Business, Industry, Technology

Benchmarking AC/DC power supplies is a critical task for any engineer or R&D team. But to get an accurate picture of how a power supply will perform in the real world, you need more than a simple resistive bank. You need a way to simulate real-world, dynamic load profiles. That’s where programmable electronic loads come in. They allow you to test for true load regulation, transient response, power factor, and efficiency, ensuring your designs are both accurate and reliable.

In this hands-on tutorial, we’ll cover everything you need to know to get started. You’ll explore why programmable electronic loads are a game-changer compared to traditional methods, and we’ll break down the different load modes, showing you how to choose the right one for your specific needs. The guide also provides a step-by-step lab setup and test procedure, explains the key metrics to capture, and shares best practices for automating your tests. To make the concepts even clearer, we’ll walk through real-world case examples and common pitfalls to help you avoid mistakes.

Whether you’re building, qualifying, or validating AC/DC power supplies, this guide will give you the tools and best practices to benchmark effectively and with confidence.

The Advantages of Programmable Electronic Loads

Electronic Loads vs Resistive Loads

Traditional resistive loads are static and inflexible, offering only a single, fixed resistance value. To get a true picture of how your power supply will perform in the real world, you need a far more dynamic approach. Programmable electronic loads give you precisely that, offering unparalleled control, repeatable results, and comprehensive test coverage.

Instead of a fixed resistance, a modern electronic load allows you to:

  • Emulate real-world load profiles: You can simulate complex, dynamic scenarios, including pulsed loads, non-linear current draws, and even variable power factor. This allows you to stress-test your power supply under conditions that it will actually face in the field.
  • Switch modes instantly: You can switch between all the major modes—Constant Current (CC), Constant Voltage (CV), Constant Resistance (CR), and Constant Power (CP)—with precise control, all without having to physically re-wire your setup. (Source: Techtronix)
  • Reduce waste and save energy: Bidirectional, regenerative loads have the advantage of returning energy to the grid, preventing it from being wasted as heat. This not only makes your lab more energy-efficient but also significantly reduces the need for expensive cooling infrastructure in high-power test environments.

These advanced capabilities provide engineers with much greater insight into power supply behavior, which is critical for ensuring compliance, guaranteeing reliability, and validating performance.

2. Understanding Load Modes & Advanced Features

Constant Current, Voltage, Resistance & Power Modes

To effectively benchmark a power supply, you need the right tools to simulate a wide range of conditions. Programmable loads offer a suite of modes that make this possible:

  • Constant Current (CC) Mode: The load draws a fixed current regardless of the voltage. This is perfect for stress-testing a power supply’s current-limit behavior and its overload protection.
  • Constant Voltage (CV) Mode: The load maintains a steady voltage across its terminals, with the current varying as needed. This mode is excellent for simulating voltage-regulated circuits and testing battery charging circuits.
  • Constant Resistance (CR) Mode: The load behaves like a fixed resistor. In this mode, the current and voltage vary proportionally according to Ohm’s law, making it ideal for simulating simple resistive loads.
  • Constant Power (CP) Mode: The load adjusts its voltage and current to maintain a steady power draw. This is a highly dynamic mode, often used for discharge testing and simulating applications with a constant power demand, like certain motors or LEDs.

Modern loads also support transient or dynamic testing, which rapidly switches the load level to capture how a power supply responds to sudden changes. This is essential for measuring step response, overshoot, and regulation behavior. (Source: cadence)

AC Load Features

For AC power supplies, advanced features allow you to go even further. You can simulate high crest factor and variable power factor scenarios, as well as the inductive or capacitive load behavior of motors and switching devices. Furthermore, regenerative AC load modes feed excess energy back to the grid, which not only minimizes waste heat in the lab but also improves safety and reduces operating costs. These sophisticated features enable realistic testing of power supplies under the non-linear and distorted conditions they will likely face in a real deployment.

Choosing the Right Electronic Load for Your Benchmarking Needs

Selecting the right programmable electronic load is a strategic decision that directly impacts the quality and efficiency of your testing. The key is to choose a device that not only meets your current needs but also provides the flexibility for future projects.

When evaluating your options, focus on these critical specifications:

  • Voltage, Current, and Power Range: Ensure the load’s maximum ratings meet or exceed those of your device under test (UUT). Whether you are working with single-phase or three-phase AC, or high-power DC, a load with a sufficient operating envelope is non-negotiable.
  • Advanced Measurement Capabilities: For comprehensive analysis, look for a load with built-in measurement features for metrics like power factor (PF), total harmonic distortion (THD), crest factor, and inrush current. These features give you a much deeper understanding of your power supply’s performance.
  • Regenerative Capability: If your work involves high-power testing, a regenerative electronic load is a significant asset. By feeding energy back to the grid, it drastically reduces heat dissipation and the need for large cooling systems, leading to a more efficient and cost-effective lab environment.
  • Interfaces for Automation: To integrate the load into your workflow and ensure repeatable, scalable testing, make sure it supports industry-standard interfaces like GPIB, LAN, and USB with SCPI protocol support for remote automation.

Leading vendors like Kikusui offer advanced electronic loads—such as the PLZ-5W and PXZ series—that provide these advanced features, giving you the tools to perform highly accurate and efficient benchmarking.

Setting Up Benchmark Tests: Step‑by‑Step Lab Procedure

To conduct accurate and repeatable tests, you need a methodical approach. The lab setup is straightforward, but the procedure is what unlocks meaningful data about your power supply’s behavior.

Step-by-Step Lab Procedure

  1. Set Up Your Hardware: The fundamental setup involves connecting your device under test (UUT)—the AC/DC power supply—to the programmable electronic load. For detailed analysis, a power analyzer or precision meter should be placed in the circuit to capture key metrics like voltage, current, power, power factor, and total harmonic distortion (THD).
  2. Perform a Warm-Up Phase: Before any measurements, energize your UUT and allow it to stabilize for a defined period. This is crucial because a power supply’s output can drift as its internal components reach thermal equilibrium. Record the open-circuit baseline voltage and input current to establish a reliable starting point.
  3. Conduct a CC Mode Sweep: Use the constant current (CC) mode to apply a series of static loads. A common practice is to test at 10%, 50%, and 100% of the rated current. As you apply each load, meticulously record key performance indicators such as load regulation, voltage drop, ripple, and the thermal profile of the supply.
  4. Test Other Load Modes: To simulate different real-world conditions, use the other modes.
    • Constant Voltage (CV) and Constant Resistance (CR) modes can be used to test for overcurrent, short-circuit, and other protection behaviors.
    • Constant Power (CP) mode is ideal for discharge testing and simulating applications with a steady power draw.
  5. Run Dynamic/Transient Tests: This is a vital step for validating real-world performance. Program your electronic load to trigger rapid changes in the load level (for example, from 10% to 100% current). Use an oscilloscope or a fast-sampling meter to capture the output voltage’s response, looking for critical metrics like overshoot, settling time, and recovery time. (Source: cadence)
  6. Add AC Load Specifics: If you are testing an AC power supply, use the advanced features of your electronic load to simulate distorted conditions. Emulate power factor distortions, high crest factor loads, or inductive and capacitive scenarios to mirror the challenging environment of a real deployment. (Source: Programmable Power)

By following this comprehensive procedure, you ensure that your power supply is not only compliant with specifications but also reliable and robust across all realistic load conditions and operational states.

Key Metrics for Comprehensive Benchmarking

AC/DC Power Supply Testing

A thorough benchmarking procedure is only as good as the metrics you capture. By focusing on these key performance indicators, you can get a complete picture of your power supply’s behavior and reliability:

  • Load Regulation: This metric tells you how well your power supply maintains a constant output voltage as the load current changes. A power supply with good load regulation ensures that the components it’s powering—even sensitive ones—receive a stable voltage regardless of their demand. We measure this as the percent change in voltage from a no-load to a full-load state.
  • Transient Response: Power supplies rarely operate under a static load. This metric evaluates how quickly your power supply reacts and recovers when the load changes abruptly. Using an oscilloscope, you can capture crucial data like the rise and fall times, as well as any overshoot or undershoot in voltage. A fast recovery time is essential for power supplies feeding dynamic, real-world loads.
  • Efficiency & Power Factor: For AC supplies, these metrics are vital for both energy conservation and regulatory compliance. We document the power supply’s efficiency (output power divided by input power) at key load points. Power factor (PF) and total harmonic distortion (THD) are also critical, as they indicate how efficiently the supply uses the power from the grid and its impact on overall power quality.
  • Ripple & Noise: Even on a “stable” DC output, there will always be a small, unwanted AC component known as ripple and noise. This is measured with an oscilloscope under both steady and transient loading and can be a critical factor for sensitive analog and digital circuits.
  • Stability Under Non-Linear Loading: A final, critical test is to assess the power supply’s stability when faced with non-linear loads, such as rectified, inductive, or capacitive ones. This ensures that the control loop is robust and can handle the complex load profiles that are common in modern electronics.

By capturing these metrics across all the operational modes and payloads you expect in production, you can be confident that your power supply will perform reliably in the field.

Automating Tests and Logging Data

Manually running a power supply test with a programmable load is a great way to start, but to achieve true efficiency and consistency, automation is key. Instead of manually adjusting load levels and recording data, you can leverage remote-control interfaces like USB, LAN, or GPIB to script entire test sequences.

This approach allows you to:

  • Create pre-defined sequences that ramp loads through various modes (CC, CV, CP) and conditions, ensuring every test is run exactly the same way.
  • Automatically trigger data capture at each step, collecting metrics like voltage, current, power, power factor, and temperature without the risk of human error.
  • Export results directly to common file formats like CSV, or even integrate them with analysis tools such as Excel, MATLAB, or Python for deeper insights.

The benefits of this automated workflow are significant: you get guaranteed repeatability, a version-controlled history of your test definitions, much faster regression testing, and simplified documentation for compliance purposes.

Real-World Applications and Use Cases

UPS, Inverters, and Telecom Power Supplies

These capabilities make programmable electronic loads essential—not just convenient—for robust power supply validation across a wide range of industries.

For example, when testing UPS and inverters, programmable loads with high crest factor and power factor variation are used to accurately simulate the surge loads and complex draw profiles of a data center or critical infrastructure. This is the only way to truly validate the system’s response during transitions to battery-backed power.

Similarly, in telecom, engineers use constant power (CP) and dynamic modes to emulate the unpredictable shifts in network traffic, ensuring that the power supply remains efficient and stable as the load changes.

For battery systems, CP mode is the ideal tool for discharge testing, as it provides a constant power drain that accurately characterizes capacity, lifetime, and ripple behavior, giving you a clear picture of the battery’s true state of health. These real-world examples highlight why a programmable load is a fundamental tool for any validation process.

Best Practices & Common Pitfalls in Benchmarking

While programmable electronic loads offer immense flexibility, a few key practices can make the difference between accurate, repeatable benchmarks and misleading, or even dangerous, results. First and foremost, always ensure you avoid overload by using an electronic load with ratings that exceed your device under test’s (UUT’s) maximum specifications. This simple step prevents equipment damage and ensures the integrity of your test data.

When conducting high-power tests, leveraging regenerative modes is a best practice that goes beyond just saving energy. By feeding power back to the grid, these loads significantly reduce waste heat, which minimizes the need for costly HVAC and ensures a more stable thermal environment for your delicate test equipment. Additionally, for AC supplies, it is critical to set the correct crest factor and power factor in your load settings. Misconfiguration here can lead to excessive peak currents that distort your results and fail to reflect real-world operating conditions.

Finally, always prioritize instrument calibration and safety protocols. Make sure all your measurement tools and power analyzers are regularly calibrated and that your test system’s temperature has stabilized before logging data. When performing aggressive fault testing, always establish proper safety protocols, including interlocks and short-circuit protection, to protect both your equipment and your team. Proper planning around these pitfalls is key to ensuring consistent results and a safe lab environment.

Conclusion: Elevate Your Power Supply Validation

Benchmarking AC/DC power supplies using programmable electronic loads is a critical practice that delivers unmatched flexibility, accuracy, and real-world relevance. This guide has walked you through why this approach surpasses traditional resistive testing, the core load modes and their applications, the best practices for selecting and setting up your system, key metrics to capture, and how to use automation to scale your testing across product builds.

By applying the principles in this guide, you can move beyond basic testing and ensure your power supplies are truly robust. To help you take the next step:

  • Build Your Own Protocol: Put your knowledge into action by defining a benchmark protocol that outlines the sequence of modes, load levels, metrics, and equipment you’ll use for your specific products.
  • Explore Templates and Tools: Look for benchmark checklists or test script templates tailored to your product class. Many vendors and engineering communities offer these to help you get started.
  • Engage and Improve: Consider sharing your test scripts or results within engineering communities for peer review and continuous improvement.

Are you ready to elevate your power supply validation?

Whether you are benchmarking a new design or validating a production unit, the right tools can make all the difference. Share your best strategic decisions in the comments.