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Building a Simple Electronic Load for Testing Power Supplies

Welcome to the EEV Blog, an Electronics Engineering video blog focused on electronics design. In this episode, host Dave Jones discusses the need for an electronic load to test the performance of DC to DC converters and switch mode power supplies. He argues that traditional methods involving power resistors are not efficient or practical and proposes building a simple electronic load using junk box components.

The Need for an Electronic Load

Jones introduces the need for an electronic load to characterize the performance of switch mode power supplies, particularly their efficiency and performance over the entire load range.
Traditional methods involving power resistors are deemed impractical, leading to the proposal for a simple electronic load for testing power supplies.

Designing the Electronic Load

Jones explains the basic requirements for a simple electronic load, which essentially acts as a constant current sink, drawing a specified constant current from the power supply regardless of its voltage.
He outlines the limitations of using classic circuits like the LM 317 as constant current generators and identifies the need for a more efficient solution.

Simple Building Block Circuit

Jones introduces a basic N-Channel MOSFET circuit based on a logic level MOSFET (MTP 305) and an LM 324 op-amp as a series pass transistor.
The circuit allows for adjustable constant current load based on a voltage input, providing a simple and effective electronic load for testing power supplies.

Incorporating a Panel Meter

Jones explains the addition of a panel meter to the electronic load for monitoring the set current, eliminating the need for using a multimeter in series to measure the current.
He advises on the selection of suitable panel meters designed for common ground connection and shares the specific circuitry involved.

Building and Testing the Electronic Load

Jones showcases the finished design of the electronic load, highlighting the use of a pre-wired PCB and the inclusion of a 10-turn pot for fine current adjustment.
He demonstrates the functionality of the electronic load, showcasing its ability to handle variable current loads and the integration of the panel meter for accurate current measurement.

Power Dissipation and Heat Sink Calculation

Jones delves into the importance of calculating power dissipation and heat sink requirements for the electronic load, providing a basic back-of-the-envelope calculation for determining the heat sink's temperature rise.
He conducts a practical temperature measurement to confirm the accuracy of the calculated heat sink temperature rise, validating the effectiveness of the electronic load design.

Versatility and Applications

Jones discusses the versatility of the electronic load, highlighting its potential applications for testing power supplies and generating various load types, including constant power, resistance, and pulse loads.
He emphasizes the importance of using the electronic load to graph power supply efficiency and performance over different load conditions, hinting at a future blog episode to explore this topic further.

In conclusion, Dave Jones demonstrates the process of building a simple and effective electronic load using readily available components, offering a cost-effective solution for characterizing and testing power supplies. The versatility and practicality of the electronic load make it a valuable tool for electronics engineers and enthusiasts alike, enabling detailed analysis of power supply performance and efficiency.