Session 6

By the end of this session you will:

  • Be able to measure, tabulate and graph the forward and reverse characteristics of a zener diode by practical measurement and by simulation
  • Know how a zener functions and why it is the perfect choice for certain types of circuit

The first thing that needs to be said about a zener diode is that unlike a normal diode, a zener is designed to operate in reverse bias and that its reverse bias breakdown voltage is much lower (usually) than that of a normal diode.

It is further designed to maintain a steady voltage across itself as long as the input voltage is higher than the switch on voltage (the zener voltage). To achieve this zener diodes require an operating current which is usually something like 10 mA. The next circuit I will show you is the most basic zener regulator circuit. The regulator part means that the zener will ‘regulate’ ie the voltage across itself despite changes in the input voltage.

The purpose of an effective regulator is to maintain a steady output voltage despite changes in the electrical load. This is where a zener fails as it cannot source current and begins to fail if there the changes in the operating current are too large.

The next diagram shows how the zener functions.


zener diagram

Rather than spend ages explaining all of the subtleties of Zener diodes, I have found a resource which does excellent simple explanation and also goes into some depth.


The following video goes into a great deal of detail as to how a zener functions.

The next video gives you all the information required to test the zener characteristic practically.

Complete the tasks as detailed in assignment 1