Chapter 15
  Diode
  Diode rectigies converts alternating current (AC) to direct current (DC).
Diode symbol of diode
Symbol

The diode is made of two different parts. One part is called p-type and other part is called n-type. In between, we call it the p-n junction. P--type is silicon mixed with boron and n-type is silicon mixed with phosphorous. In order to explain how it works, we must know about the octet rule and valence electrons.

The octet rule is that bonded nonmetialic atoms has eight electron outermost shell or energy level. It means that when two chemicals react each other and produce a product, its outer shell has eight electrons.

The valence electrons are the electrons moving aroung the most outer shell of an individual atom and they are often involved into chemical reaction bonding.

In the periodic table, we can see all the names of elements and those are arranged into different periods and coulmns which are arranged by its chemical and physical characteristics. At the most right coulmn, we can see very familiar names which are helium, neon, argon, krypton, xenon, radon. We call them the noble gases because they don't chemically react with other chemicals. They have 8 valence electrons and without chemical reaction it stisfies the octet rule. The chemical reaction occurs because other elements want to have eight valence electrons in their outer energy level. Sodium which has 1 valence electron and chlorin which has 7 valence electrons can easily react each other. When they become sodium chloride which is salt, it is very stable because they have eight electrons in their outer energy level and the octet rule is satisfied.

 

  P-type: Silicon has 4 valence electrons and boron has 3 valence electrons. When they are mixed together, their total valence electrons are 7. The octet rule is not satisfied and they are willing to accept one more electron. Let's say there are holes in that compound or crystal.

N-type: Silicon mixed with phosphorous which has 5 valence electrons. Their total valence electrons are 9. The octet rule is violated. They are willing to lose this one extra electron. Let's say there are extra electrons.

 

  A

p-n type current flows

Diode p-n type
There are holes in the n-type part of p-n junction and extra electron on the side of p-type of p-n junction. When p-type part is connected to the positive part of the battery, it attracts the electrons. Therefore, electrons in n-type start to move to the other part the p-type. Because it want to lose one valence electron on the outer shell, it is easier to push these out to other part of diode. Then electron in p-type move to positive side of battery because the positive part of battery pull down electron in the hole. Therfore the diode become a conductor.

  B

n-p type current doen't flow

Diode n-p type 1

Diode n-p type 2
If there are no voltage on the circuit, electrons does not move. When n-type is connected to positive part of battery and take one electron from it, the electrons from negative part of battery fill in one hole in p-type part of diode. If the battery take four electrons from n-type, there will be four electrons fill in holes of p-type part. But when it occurs, there is no more electrons left in n-type, so the battery cannot take electrons from n-type part of diode and it becomes an insulator. However, if there is on more electron in n-type (when all the holes in p-type are filled, it basically looks alike diagran A on above), there will be flow of charge because taking last one electron in n-type will bring one electron from p-type part.

 

  Because whatever current starts from a power source, it has to wait before diode. The diode takes electrons one by one so it becomes a direct current. Also if p-type has many holes and n-type has that many electrons, it can take big current.

There are more than 50,000 types of diode with variety of current.

   
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