Diodes

Introduction to Diode

Diode is like a one way electronic switch. One way means that current can only flow in one direction.

Electronics switch means that no manual on/off operation required but can be controlled by suitable voltage application.

The base material to make diode is semiconductor  such as Germanium and Silicon. These semiconductor materials in their pure stage are not very conductive. (That is why they are called semiconductor). To increase their electricity carrier property, they are doped (infused) with some other elements such as aluminum( group III in periodic table)  and phosphorus ( group 5 in periodic table). A silicon/germanium doped with aluminum will produce a P type ( more positive carriers) while silicon / germanium doped with phosphorus will produce N type ( more negative carriers).

The diode is made by combining P and N type material together. The P type is called anode and the N type is called cathode (K).

As mentioned earlier, diode behaves like a switch that conduct current in one direction only. Which direction is the flow of current? Well follow the sign of the diode, the triangle looks like the arrow head! Current flows in that direction. If diode behaves like a electronic switch, then you can turn it ON or OFF electronically but how ??

To turn on a diode, the anode ( P side) must be more positive than the cathode side by at least 0.6/0.7V for silicon and 0.3V for Germanium. This is called the threshold voltage. It is the minimum voltage required to turn on a diode. 
However for LED type of diodes, the voltage can be about 1.5V depending on the color of the LED. This voltage requirements are for practical diodes (used in real life). For ideal diodes, as long as anode is more positive than cathode, the diode conducts current. Hence the threshold voltage for ideal diode is 0V. In reality ideal diodes do not exist. There is always a minimum threshold voltage required to turn on a diode.

Different types of diodes based on application

a. Light Emitting Diodes  (LED)

Different colored led requires different threshold voltage to turn on. In diagram below, the green led requires 2.1V while the red led needs only 1.7V. 

b. Rectifier diode

A rectifier diode lets electrical current flow in only one direction and is mainly used for power supply operation. Rectifier diodes can handle higher current flow than regular diodes and are generally used in order to change alternating current into direct current.

c. zener diode

Zener diode is quite special and different  from other types of diode. In forward bias, it works as normal diode. In reverse bias, when reverse voltage across  Zener diode is increase to rated value, the voltage drop across diode becomes steady ( fixed and will not increase any more). This voltage drop is known as zener voltage and this property is used to regulate voltage across load. The load will not get damaged by

Self-Test

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