Things to Know About Diodes

Concept, structure, operation and polarization for Diode

Diode is a familiar electronic components, it seems that in the electronic and electronic devices that we use every day, many items use diodes. However, little is known about its existence as well as detailed information about it remains a mystery to many people.

What is diode?

Diodes are passive and nonlinear electronic components that allow current to flow through it in one direction but not the other, using the properties of semiconductors.
* Symbols and shapes of Diode:

Symbols and shapes of Diode

Structure of Diode

A diode is a semiconductor electronic device, so it is made of a mixture of silicon, phosphorus and bori. These three elements are doped together to create two layers of P and N type semiconductors that are in contact with each other. At the contact surface, the excess electrons in the N semiconductor diffuse to the semiconductor area P to fill into holes => forming an electrically neutral ion layer => this ion layer forms an insulating domain between the two semiconductors.

The diode pole facing P class is called Anot (symbolized A), the other pole facing N class is called Catot (symbolized K). The most basic characteristic of a diode is that it only allows current to flow from A to K.

The working principle of diode

Principle of operation of the semiconductor diode as shown below

Schematic diagram of operation of a semiconductor diode

(1) The P-type semiconductor block contains many free holes that carry a positive charge, so when combined with the N-type semiconductor block (containing free electrons), these holes tend to have diffuse motion to the N block. At the same time, the P block receives additional electrons (negative charge) from the N block. The result is that the P block is negatively charged (holes and electrons excess) while the blocks N are positively charged (electrons and holes missing).

Negative charges on the P block and the positive on the N block form a voltage called the contact voltage (UTX). The electric field generated by the direction of the voltage from the N block to the P block should hinder the diffuse motion and so after some time since the two semiconductor blocks are joined together, the diffusion movement ceases and persists. at contact voltage. Now we say the P-N contact is in equilibrium. The equilibrium contact voltage is about 0.6V for diodes made of Si semiconductors and about 0.3V for diodes made of Ge semiconductors.

(2) At the boundary on either side of the junction, some electrons are attracted to the holes and as they approach each other, they tend to combine to form neutral atoms. And now the border on the sides of the junction is called a poor region because of the scarcity of free conducting particles. This region does not conduct electricity well, unless the contact voltage is balanced by an external voltage. This process can release energy in the form of light (or electromagnetic radiation of nearby wavelength).

(3) If the external voltage is set against the contact voltage, the diffusion of the electrons and the hole are no longer hindered by the contact voltage and the junction area conducts electricity well. If the external voltage is applied in the same direction as the contact voltage, the diffusion of the electrons and holes is further prevented and the poor region becomes poorer free conductive particles. In other words diodes only allow current to flow through it when the voltage is applied in a certain direction.

→ External voltage is opposite the contact voltage that generates the current. External voltage in the same direction contact voltage prevents current.

* Properties of Diode

As mentioned above, diodes guide electricity in one direction from the anode to the cathode.

According to the principle of the current flowing from high voltage to low voltage, if you want the current to flow in the diodes from the high voltage to the low voltage, you need to set an higher voltage in Anot. in Catot.

+ Then we have UAK> 0 and opposite of contact voltage (UTX). Therefore, in order to have the current through the diodes, the electric field generated by UAK must be stronger than the contact field, ie: UAK> UTX. Then part of the UAK voltage is used to balance the contact voltage (about 0.6V), the rest is used to generate a favorable current through the diode.

+ When UAK> 0, we say forward biased diodes and current through the diodes is called positive current (usually referred to as IF ie IFORWARD or IDIO IDIODE). The positive current flows from Anot to Catot.

+ When UAK has enough balance with the contact voltage, the diode becomes very good conductive, that is, the resistance of the diode is very low (about a few dozen Ohm). Therefore, the voltage to produce a forward current is usually much smaller than the voltage used to equalize the UTX. Normally, the voltage part to be balanced with UTX needs about 0.6V and the forward voltage part is about 0.1V to 0.5V depending on the forward current of several tens of mA or up to several amps. Thus, the value of UAK is enough to have the current through the diode about 0.6V to 1.1V. The threshold of 0.6V is the threshold where the diode starts to conduct and when UAK = 0.7V, the current flows through the diode a few dozen mA.

How to polarize Diode

Positive bias for Diode

When we apply positive voltage (+) to the Anot and negative voltage (-) to the cathode, then under the effect of voltage interaction, the insulation domain shrinks.

+ When the voltage difference between the two poles reaches 0.6 V (with Diode type Si) or 0.2 V (with Diode type Ge), the area of the insulation domain decreases to zero => Diode starts conducting.

+ If the source voltage continues to increase, the current through the diode increases rapidly, but the voltage difference between the two poles of the diode does not increase (remains at 0.6 V)

→ When the diode (type Si) is biased, if the forward bias voltage <0.6V, there is no current through the diode, if the positive polarity reaches 0.6V, then the current passes through the diode then the current passes through Diode increased rapidly but the pressure drop remained at 0.6V.

Positive bias for diode

The characteristic of the forward voltage through the diode

Reverse polarity for diode

When the reverse polarity of the diode means supplying power (+) to the cathode and (-) to the anode, under the interaction of reverse voltage, the insulating domain widens and prevents the current from passing through the junction. Diode can withstand reverse voltage of about 1000V, the diode is punctured.

Reverse polarity for diode

Where to buy quality diode?

Most electronics components stores sell diodes. However, whether the diode has a quality or not, whether it's genuine or not, and whether the price is soft or not is another story.

Stores on Diode cheap, quality: All about Diode

For those who study electricity and electronics, you must definitely know about the structure, the principle of operation and the polarization of the diode already, and others who do not learn but accidentally know it is good. In short, whoever you are, you should save this useful knowledge, there will be times when you need it!

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