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Session 2533

A Realistic, Insightful Demonstration of a Bridge Rectifier

Herbert L. Hess Department of Electrical Engineering University of Idaho, Moscow, Idaho

Abstract A simple, insightful demonstration of a four-diode bridge rectifier is presented. Light emitting diodes (LEDs) replace the rectifier diodes. An ordinary function generator provides the voltage input and maintains the operation at safe voltage levels. Building the circuit and operating it is described. Setup and simple calibration and troubleshooting procedures are explained. Some notes on theory of operation supplement the presentation. The demonstration circuit is safe for classroom operation and is easily portable giving insight into rectifier operation by the dramatic effect of flashing lights.

Introduction Single phase diode bridge rectifiers are a workhorse of power electronic energy conversion. A host of electronic systems draw energy through power supplies containing such rectifiers. These systems cover a range in size and purpose from simple plug-in converters to the switch mode power supplies that are a common element of most personal computers.

Learning and understanding their operation and design can be challenging. There are several textbooks that do an excellent job of explaining how these rectifiers operate.[1] Nonetheless, seeing such a circuit in operation often helps the student understand how it works. Complicated or unfamiliar instrumentation can slow the learning down, but a working circuit with simple visual impact can dramatically enhance understanding.

In this paper, a simple demonstration using a working rectifier helps introduce the circuit's operation to the student. The circuit is intended as introductory, with flashing lights to illustrate important points. The circuit is portable and construction is well within the capability of an undergraduate electrical engineering program, requiring just a small piece of circuit board and a simple function generator. Setup and troubleshooting requires no more instrumentation. The insight gained by its simple operation helps introduce students to the operation of switching rectifier circuits.

Circuit Construction The topology for this circuit is that of the standard four-diode bridge rectifier as shown in Figure 1. The diodes are light-emitting diodes (LEDs) rather than rectifier diodes. Numbered diodes D1, D2, D3, and D4 are all the same color, for example, red. Output diodes Dx and Dy are a different color than the other four diodes, for example, green or yellow. Polarities are as shown in the diagram. The forward voltage drop of typical cheap LEDs is approximately 2.0 Volts at a rated forward current of 20 mA.

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Hess, H. (1999, June), A Realistic, Insightful Demonstration Of A Bridge Rectifier Paper presented at 1999 Annual Conference, Charlotte, North Carolina. 10.18260/1-2--7914