What is a diode?

Do you know what a diode is and how it works? As different as this term sounds, it is certain that you have seen a diode and how do we know that? Well, it’s very simple! If you watch something on an LED monitor or a cell phone with an LED screen, you are literally looking at millions of diodes! Each little light that lights up in the electronics you have in your home is a light-emitting diode, which is popularly known as LED !

What is a diode?

A diode is an electronic component that allows electrical current to flow only in one direction. A simple analogy that we can make is to compare a diode to a valve that only lets water flow in one direction, that is, the diode does the same thing with the electric current. This is well exemplified in the image below:

The diodes work like valves, allowing current to flow in only one direction, respecting its polarity!

The diode is a component with 2 terminals, where the schematic symbol itself indicates the polarity. If you look closely at the diode symbol, you can see a triangle that forms a small arrow, indicating the direction in which electrical current is allowed. In the diodes, current flows from the anode to the cathode, as shown in the following image:

To identify the polarity of the diode is very simple, the current passes from the anode to the cathode!

What is the functionality of the diodes?

We can say that the diode has several applications and one of them is to act as a rectifier, converting alternating voltage into continuous. But a diode is not a perfect electricity valve, it takes a little bit of energy to work and when current flows through the diode, some power is always dissipated in the form of heat. This is realized through a voltage drop of approximately 0.7V.

Therefore, the higher the current, the greater the heating in the diode. So, we know that the voltage drop can vary according to the current, the temperature, and the type of diode too! But to facilitate the understanding of this voltage drop, let’s take an example and in it we will consider that the drop is always 0.7V.

To make a diode conduct electricity you need to put at least 0.7V from the anode to the cathode! With less than that, the silicon diode is not able to conduct electricity. So, if you put 5V between the anode and cathode of a diode, there will be current flowing through the diode and the voltage in the diode will be 0.7V, leaving 4.3V for the rest of the circuit, as shown in the following image:

How does the voltage drop in the diode happen?

This 0.7V voltage drop can be a problem in some circuits and that is why there are diodes with different characteristics, even with a much lower voltage drop.

How to choose a diode?

As already mentioned, the diode dissipates a little heat, that is, knowing the maximum power it can withstand is essential for choosing the appropriate diode. The power in the diode is calculated by multiplying the voltage drop in the diode by the current flowing through it.

To exemplify this, imagine that a current of 500mA is passing through a silicon diode. The typical voltage drop in this diode is 0.7V, so the dissipated power will be 0.5A multiplied by 0.7V, totaling 0.35W or 350 mW, as shown in the image below:

The choice of the correct diode depends on several factors, including the voltage drop!

It may not seem like much, but it is a power that can make the diode warm-up well! Therefore, it is very important to know the maximum current that the diode can support. This information is present in the manual or in the diode datasheet.

Can I use 2 diodes in parallel?

The answer is no! The current will not be divided proportionally between the diodes as with the resistors, that is, there is no point in placing two diodes in parallel to support more current. What will happen if you do this, is that one of the diodes will be faster and conduct the current first, consequently it will receive more current because of this.

Another interesting feature that differentiates the diodes is the switching speed! Each diode takes time to “close and open the valve” which allows current to flow. Therefore, it is important to understand that there are diodes to be used at low frequencies such as those connected to rectifying bridges in the alternating network, and there are also faster diodes for other applications, which support much higher frequencies.

What is maximum reverse diode voltage?

This is one of the most important characteristics of diodes! Going back to the analogy of the water valve used in the first example of the article, the maximum reverse voltage would be like the maximum pressure that the valve can withstand without letting the water leak!

Watch the video below and in it you will see in practice how the heating in the diode occurs, how to test the polarity, how to determine which is the maximum reverse voltage and many other tips in a very dynamic way.

The best way to learn about diodes is to search the datasheets of various models and see which ones can be used in each application. Analyze well, as there are dozens of types and classifications of diodes. In addition to general-purpose diodes, the most common are LEDs, Zener diodes, signal diodes, power diodes, photodiodes, laser diodes, varicap, etc. Anyway, the list is huge! If you have any questions, leave them in the comments and we will be happy to answer them!