What is Diode?

What is Diode? How Does It Work? What Does It Do?


In this article, we will explain the concept of diode by searching for answers to questions such as what is diode, how it works, where it is used. Diode is the circuit element that transmits the current in one direction with its general expression. To put it in more detail, some substances are frequently used in diode and other semiconductor circuit elements and you will hear it frequently. The most commonly used substances are Silicon (Si) and Germanyum (Ge). The electrical properties of silicon and Germanium are enhanced thanks to the substances added by the additive process.


If elemental atoms have 1 electron in their final orbit, they show the best conductivity. Because the goal is to gain additional (+) value to the atom by creating free electrons (Copper Cu+, Silver Ag+, Gold Au+).


Silicon (Si) and Germanyum (Ger) also show semiconductority by having 4 electrons in their final orbits. The use of silicon has become quite common recently. Silicon is also used in diodes as semiconductor and semiconductor. If silicon exchanges electrons with Arsenic (Ace), silicon 1 is reduced by taking electrons and acts negatively (Si-5). This condition is called N-type (Negative) semiconductivity. If it makes its electron exchange with Boron(B), it acts positively by giving 1 electron (Si+3). This condition is also called P type (Positive) semiconductivity. As a result, N is formed as an extra electron and P consists of empty orbital. The P pole becomes the anode, the N pole becomes the cathode, and excess electrons are packed into empty orbitals, moving from the anode to the cathode (P-N Junction). Thus, with the use of the diode, the current progresses from the anode to the cathode.


If all the orbitals in the last orbits of element atoms are full, that is, containing 8 electrons, then they form the best insulator. These substances have little or no conductivity (Neon, Argon, Radon and other inert gases).

How Does Diode Work?

When P and N type materials are combined in a crystal structure, they create a P-N jonction between the two regions. This element is known as semiconductor diode and passes current in one direction. P-N jonction is the basis of diode, transistor and other semiconductor elements. It is a circuit element with two ends in the form of a diode, anode and cathode. There are a large number of free electrons in the N zone and numerous holes in the P zone at room temperature before the jonction occurs. Electrons and holes move freely in all directions. At the moment of jonction, some of the electrons move towards the P area. The reason for this movement is the diffusion current.


If you think about the diffusion current; this current is the propagation towards where the electron density is less than where there is a lot of it. Electrons that pass into the P zone merge with the holes. In the N region, there are atoms (+) that lose their electrons and atoms (-) that lose their holes by taking electrons in the P region. As a result, there are many positive and negative ions near P-N jonction. Not all electrons in zone N can cross into zone P. Electrons in the N region are attracted by positive ions. In order for these electrons to pass into area P, they must overcome the thrust of negative ions.

The ends of the diode are also determined by positive (+) and negative (-) signs. The "+" is called the anode, the "-" the other is called the cathode. When the anode of the diode is applied to the positive (+) pole of the voltage source and the negative (-) pole of the cathode of the source, the diode passes to the diode. In other words, their resistance in one direction is negligiblely small, and their resistance in the other direction is very large. The direction in which the resistance is small is called "the right direction", the direction in which it is large is called the "opposite direction".

What are the Uses of Diode?

It is used as a rectifier, detector, modulator, limiter, switch in electrical and electronic field from diodes. Rectifier diodes are used in power supplies to convert AC currents to DC. They can carry high currents and withstand high inverse peak voltages. However, they are usually used in low frequency circuits such as 50-60 Hz. Signal diodes are used as demodulators (signal separators) in logistics (numerical) circuit elements or radio frequency (RF) circuits.

In other words, in addition to being sensitive to working at high frequencies, signal diodes can also operate at low voltages and currents. Rectifier and signal diodes can be made of silicon and germanyum. When the current is passed through the diodes made of germanyum, there is a voltage drop of about 0.2 Volts on them, while in diodes made of silicon, this value is between 0.6 and 0.7 Volts. Because of this difference, the germanium substance is mostly used in the production of signal diodes. We will prepare and publish the varieties of diode in another article.

Diode Characteristics:

It is possible to understand the behavior, i.e. characteristics of an electronic circuit sief, by looking at the current-voltage graph.

When we read this chart, it gives us the following basic information:


  • In order for the diode to pass current while working in the advanced polarization zone, it is necessary to reach the threshold voltage specified by the Vf. Usually this value is around 0.7V in silicone diodes and 0.3V in germanyum diodes.
  • The diode does not pass current in the reverse polarization zone up to the maximum reverse voltage indicated by Vbr. When this value is exceeded, the diode is now in the refractive zone, that is, there is also a flow pass in the opposite direction through the diode. For example, for 1N4001 diode, this value is 50V.



They are the first circuit type rectifiers that we can give as an example of the use of diodes. The Rectifier is the name of the circuit used to convert AC voltage to DC voltage.

Half Wave Rectifier:

As we know, AC voltage varies between negative and positive periods. DC voltage is only on the positive or negative side. It is possible to establish a circuit in this way by taking advantage of the diode's ability to transmit the current in one direction:

Half-wave rectifier circuit consisting of a single diode.

The circuit installed in this way is called half-wave rectifier. Since only the positive part of the AC voltage will pass through the diode, the voltage on the load will be as follows:

Half-wave rectifier output.

What is Bridge Diode (Full Wave Rectifier), Full-Bridge Rectifier?

As you will notice from the name of the circuit and the wave form, we can only benefit from half of a full cycle. In order to benefit from the entire wave, we need to install a full-bridge rectifier circuit.

Bridge Diode Connection Diagram.

There are 4 diodes in the bridge rectifier circuit. In the positive part of the wave, two diodes are transmitted, while the other two diodes are transmitted in the negative part. Thus, we benefit from both the positive and negative part of the AC voltage.

What is Radiant Diode (LED)?

LED, an abbreviation consisting of the initials Light Emitting Diode (radiant diode), is one of the most common types of diode we use in our daily lives. As well as being used in power and status indicators of our electronic devices, they are also frequently used for lighting purposes today because they are efficient.

LED Circuit Symbol

What is Zener Diode?

The Zener diode works like a standar diode when connected normally. In case of reverse connection to the circuit, they do not pass current to the level called Zener Voltage, and when this voltage is exceeded, they pass to the transmission. Zener diode is used in power supply regulator circuits thanks to this feature.

Zener Diode Circuit Symbol


What is Schottky Diode?

We learned that diodes are elements that transmit current only in one direction. When the current flows from the anode to the cathode through the diode, due to the structure of the diode, there is a certain decrease in voltage. This amount of decrease is usually as much as 0.7V in standar silicone diodes. In Schottky diodes, this value is much lower. In addition, some standard silicone diodes (e.g. 1N4007), they cannot operate fast enough at high frequencies. Schottky diode can be used to prevent this situation. Despite these advantages, schottky diodes have a drawback: Although diodes transmit the current only from the anode to the cathode, a certain amount of leakage current is transmitted in the opposite direction. The leakage current values of Schottky diodes are much higher than silicone diodes.

Schottky Diode Circuit Symbol

What is Laser Diode?


We were told that diodes were made of semiconductors. There are two types of semiconductor substances: n-type that contains electrons and p-type semiconductor substances that contain positively charged "holes". These two semiconductors are combined to obtain diode.

When the diode is normally polarized forward (in the case of applying anota positive, negative voltage in the cathode), electrons moving from the negative terminal of the power supply will want to go to positive voltage. In this case, there will be a transition from N type material to p type material. Meanwhile, the resulting energy is released as photons. This photon occurs as light because a reflective coating is used at the point where P and N type materials meet. Laser light is obtained by combining the resulting light with a lens.

What is Photodiode?

Photodiodeis a semiconductor circuit element that converts light into electric current. Photons are absorbed by photodiode and converted into electric currents. The solar panelswe use are photodiode with a very large surface.


What is Varikapdiyot?

These diodes are diodes that can change capacity values and are inverted. They are similar to capacitors by placing an insulating substance between two semiconductor substances. The capacity value is adjusted according to the distance between the conductors.As the reverse voltage value applied to the ends of the varikap diode increases, the capacity value decreases.These diodes are used in TV and radio frequency circuits.
Figure 6: Varikap Diode Polarization