Electronic E-Bytes: The Diode Dilemma

Welcome to a series called Electronic E-Bytes, where we dive into a different topic for 5 minutes every week. This week, we’re focusing on the science behind diodes, and some ways to identify different types.

According to Wikipedia, the definition of a diode is this: “A diode is a two-terminal electronic component that conducts current primarily in one direction; it has low resistance in one direction, and high (ideally infinite) resistance in the other.”

I think that sums it up pretty well, but it doesn’t explain much. Let’s find out more about the science of diodes!

Semiconductor Diodes

A diode consists of two electrodes: a cathode and an anode. A cathode is an electrode that emits (gives off) electrons. An anode collects the electrons and puts them to use.

The key function of an ideal diode is to control the direction of current flowing. Current passing through a diode can only go in one direction, called the forward direction. Current trying to flow the reverse direction is blocked.

If the voltage across a diode is negative, no current can flow, and the ideal diode looks like an open circuit. In such a situation, the diode is said to be off or reverse biased.

As long as the voltage across the diode isn’t negative, it’ll “turn on” and conduct current. Ideally a diode would act like a short circuit (0V across it) if it was conducting current. When a diode is conducting current it’s forward biased, or on.

A good way to remember the difference between the anode and the cathode is the mnemonic ACID: “anode current in diode”, meaning that the anode side is where the current goes in, or the positive side.

The problem with this section of the E-Byte is that there’s no such thing as an ideal diode. Ideally, diodes will block any and all current flowing the reverse direction, or just act like a short-circuit if current flow is forward. Unfortunately, actual diode behavior isn’t quite ideal. Diodes do consume some amount of power when conducting forward current, and they won’t block out all reverse current. There is also some amount of resistance that is introduced in any circuit, no matter what type of component you use.

Light-Emitting Diodes

By PiccoloNamek – English wikipedia, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=864610

The LED stands for light-emitting diode, so on the surface, it may appear there is any different between the LED and a common diode. Normal diodes, however, are used as resisting components in electric circuits, for a purpose, while LEDs are designed specifically to produce light as a result of the extra energy caused by their resistance.

For a good inside view of a good representation of the parts of a semiconductor diode, just look through the top of the LED and see the metal pieces inside, like in the cutaway image above. The current and the voltage also needs to be regulated much more, since the parts are more complex than semiconductor diodes, like metallic elements mixed with the silicon of normal diodes.

Zener Diodes

Zener diodes are semiconductor diodes that allow current through when the current exceeds the breakdown voltage, known as the zener voltage. They are used most in power regulators and surge suppressors.

Wrap-Up

Diodes are one of the most underrated electronic components of all time, in my opinion. The 555 would not be possible without it, nor would your computer be running right now to read this article, or do anything, for that matter. Even the transistor is basically made up of diode material. The solar cell is also dependent on diodes for its function.

Thank you for reading Electronic E-Bytes: The Diode Dilemma! For more articles and projects, click here.

Electronic E-Bytes will switch to a biweekly format, so the next E-Byte will come out on Tuesday, May 17.

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