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Diodes, Light Emitting Diodes (LEDs) and Zener Diodes


Diodes are used in logic circuits, as protection for MOSFETs and bipolar transistors and in rectifying circuits. Light Emitting Diodes (LEDs) have similar properties to diodes and are primarily used as indicators in circuits to show a logic state, for instance. Zener diodes are used to give a voltage reference. Diodes in all their forms are used extensively in a wide variety of different circuits. This short lesson looks at their properties and applications.

Learning Objectives

Lesson Content

Reading: All about diodes. Consider the first four sections - overview, forward bias, reverse bias and transfer characteristics. Make sure you can draw the symbol for a diode and the V-I graph in both forward and reverse bias. Make good notes about the action of a diode.

Video (5 min): The video has three parts, the first two look at the transfer characteristics (the V-I graph) and the last part looks at using a diode as a voltage regulator. Relate the video to the reading completed previously.

Reading: Read the rest of the webpage about diodes which looks at the uses of diodes. Make notes about protection diodes and rectification in particular. Make sure to understand the idea of a voltage reference and the conversion of output voltages to logic levels.

Video (9 min): Watch the first 2.5 minutes of the video which is about half wave rectification. Watch the rest of the video if you are interested as there are some good examples of using diodes and how diodes work.

Reading: All about LEDs. The first five sections cover the overview, forward bias, series resistor calculation, reverse bias and the transfer characteristics. Read these sections which cover all you need to know to use LEDs. Make good notes and make sure you understand how to do the resistor calculation.

Video (5 min): An Interactive White Board presentation that looks at how to calculate the necessary series resistor calculation for an LED. Make sure to work through the examples.

Reading: Complete the reading which covers the different types of LEDs that are available including 7 segment displays and high power LEDs.

Reading: All about zener diodes: The first four sections of the webpage - overview, forward bias, reverse bias and transfer characteristics - give a good overview of how the zener diode functions compared to a regular silicon diode. Read these four sections and make good notes. Make sure to know the symbol for the zener diode.

Video (5 min): The video demonstrates the basic functionality of a zener diode. Watch the video and make good notes.

Reading: The second half of the webpage looks at the applications of zener diodes in voltage regulators and to provide reference voltages in comparator circuits. Work carefully through the example calculation of the necessary series resistor.

Video (7 min): An interactive white board demonstration of how to design a voltage regulator based on a zener diode. Work carefully through the example calculations.

Exercises: Complete the exercises about diodes, LEDs and zener diodes

Lesson Review

Review your learning by working through the presentations or notes which summarise the website content.

Presentation: Powerpoint download. A presentation about diodes including forward and reverse bias, applications and germanium diodes.

Presentation: Powerpoint download. A presentation about LEDs including examples of how to calculate the necessary series resistor.

Presentation: Powerpoint download. A presentation about zener diodes including theri use in regulator circuits and examples of calculating suitable series resistors and power ratings.

Notes: PDF download. Notes about diodes, LEDs and zener diodes taken from the three separate webpages and combined into one document.

Self Assessment

Complete either the questions (pdf download) OR the on-line quiz. They are the same questions.

Questions: PDF download. Questions about diodes, LEDS, resistor calculations and the use of zener diodes.

Quiz: On-line quiz using the same questions as the pdf version but self marking. Consolidate understanding of diodes, LEDs and zener diodes.

Self Evaluation

I can: