DIODES

The main thrust of Wanna Tinker is building, testing, and using electronic gear as opposed to theory.  There are times, however, when a little theory can come in handy, such as when the electronic marvel you have just put together just sits there imitating a paper weight rather than performing electrical magic for you.  Accordingly, this tutorial is devoted to explaining the fundamentals of diodes.

I urge you to avail yourself of the many excellent sources of information about semiconductors, such as the ARRL Handbook, magazine articles, and other reference material.  I find that reference material sometimes gets a little too theoretical to be of use to me.  When I am trying to get a circuit up and running, I really don’t care to wade through a lot of theoretical discussions about the physics of why things work the way they do. I just want the quickest rout to finding where I made a wiring error, or whatever caused my circuit to fail.

Look inside your commercially built rig and you will see dozens of diodes.  Check out the insides of just about any electronic device and you will see diodes all over the place!  Diodes are one of the most useful electronic components, and one of the oldest in terms of general usage (think “crystal set” radio receivers).  Whole books could be (and have been) written about these marvelous little devices.  More importantly, diodes will be used in in the projects presented on this web site, so it will be useful for you to know a thing or two about them.  Besides that, when you know a thing or two about diodes, learning about transistors is a piece of cake  (you DO want to know something about transistors, don‘t you?).

Diodes can do an amazing variety of electronic tasks, including switching, frequency doubling, voltage regulation, temperature sensing, acting as a fixed or variable capacitor, and more.  One of the simplest and most effective product detector circuits is the diode ring mixer. 

Diodes are rated by, among other things, the amount of current they can safely pass.  A forward biased diode is like a closed switch; it will pass current.  “Forward biased” simply means the voltage on the anode is more positive than the cathode, as shown in Figure 1 (A). 

As you might suspect, a reverse biased diode will block current flow, as shown in Figure 1 (B).  There is a critical reverse bias voltage that must not be exceeded.  If this critical voltage is exceeded, the current will begin to flow in an uncontrolled manner, and the diode may turn to smoke.  There are diodes, however, that are designed to safely pass current when the reverse bias reaches a specified voltage.  These diodes are called Zener diodes, and they are effective voltage regulators.  Figure 2 shows a typical application for a Zener diode as a voltage regulator.  Notice the slight difference in the symbol for the Zener diode in Figure 2 as opposed to the symbol for the “ordinary” silicon diode shown in Figure 1.