Power diodes! What are they and what are their applications?

You know what a power diode is, do you know when we use it? What is its importance and its applications? If your answer is no or if you have any doubts on the subject, come with us to learn a little more, in this article we will cover what is a power diode without mysteries.

What is a power diode

Power diodes are semiconductor devices capable of conducting electrical current in only one direction, their functional characteristic is simply to allow the passage of electrical current or not, we can say that they work as an open switch or as a closed switch.

The diodes, unlike resistors, do not have linear behavior, so their applicability in electronic power circuits is wide like rectifiers. They can also be applied as return diodes for energy transfer, as a voltage isolator, among other possibilities.

The power diodes are basically composed of two layers, one of a type P crystal (positively charged) and a layer of N crystal (negatively charged), the junction created between them allows the passage of electrical current in a single direction, the difference of the power diodes of the common diodes is a third layer called extra N, this layer allows the power diodes to withstand higher electrical voltages.

Power diodes for application in industrial devices

As we observed, the power diodes are not formed simply by a PN junction, the extra N junction is a metal layer usually chrome, platinum or tungsten, this layer allows the diode to work with high voltages and with higher currents allowing these diodes to come working on high power circuits, another function is to facilitate the heat dissipation of the diodes since they conduct a large amount of electrical current.

Operation of a power diode

To understand how a power diode works, we need to understand the basic principle of an ideal model diode. As we saw earlier, a diode is built using P-type substances, with no electrons, that is, its predominant charge is positive, and another Type N substance, with excess electrons in this way, its predominant charge is negative.

A diode is formed when these two oppositely charged crystals are merged, forming a junction called PN, when we perform this junction the layers in the center of the junction tend to balance electrically, that is, electrons recombine, since the material type P positively charged, has a tendency to attract electrons on the type N side. When this happens, the material tends to balance the electrical charges in the center of the junction, generating an area called the depletion layer. It is important to note that this rearrangement occurs only in the center of the junction where the forces of attraction are most intense, the ends of the junction remain polarized with the original charges.

We call the center a depletion layer and it is responsible for electrically insulating one end of the diode from the other. Observe the example through the image that exemplifies the formation of a PN junction of a diode:

Formation of a pn junction in a diode and depletion layer

When a diode is reverse polarized, the depletion layer tends to expand with the attraction of opposite charges, thus the resistance to the passage of electric current becomes greater between the ends of the diode, it starts to work as an open switch isolating the electric circuit. Observe the figure below that exemplifies the phenomenon:

Diode as a reverse polarized open switch

When the diode is directly polarized the electric charges tend to compress the depletion layer since the same charges tend to repel, which causes the depletion layer to be compressed, so the depletion layer is compressed in such a way that it no longer offers great resistance to the passage of electric current, the diode starts to conduct electric current between its terminals, behaving like a closed switch in the circuit. When conducting electrical current, the diode consumes 0.7 V (for silicon diodes), we observe a small voltage drop in the original diode supply voltage. Look at the example in the figure below:

Diode as a directly polarized closed switch

The operation of a power diode is very similar to the conceptual diode presented, unlike in layer N, an extra layer of metal discussed earlier, this layer behaves with the function of the type N crystal, playing the role of layer N in the operation of the diode.

To know if a power diode is working as a closed or open switch, just pay attention to the following polarization settings:

How to identify a forward or reverse bias on a diode

Polarization modes of diodes and their behavior in electrical circuits

What are the applications of power diodes

Power diodes are widely used in industries mainly in uncontrolled or semi-controlled power rectifier circuits such as substation UPS stations and large IT servers, another very common application is the return path for inductive loads, an example of this application is the power diode known as freewheel, it works to protect the drive circuits through DC converters of large coils common in magnetic separators or large electromagnets.

When these coils are de-energized, the magnetic field remaining in the inductor generates a reverse voltage, capable of damaging the thyristors of the converters, when the reverse voltage is generated, the diode connected in parallel with the earth, becomes polarized directly and discharges the voltage to earth protecting the equipment’s thyristors.

What are the characteristics of power diodes

The main characteristics of these semi-conductors are the high capacity to conduct high electrical currents, withstands great intensities of reverse voltage without damaging their operation.

The power diodes generally promote a greater voltage drop when directly polarized, the values ​​vary according to the type of diode and its power, the voltage drop value is provided by the manufacturer.

The behavior of the power diode curves is similar to the family of diodes for electronic application.

We provide a complete video for your understanding of the operation and application of the diodes.