Introduction
There are many types of semiconductor diodes namely Selenium, Germanium and Silicon types. Selenium type is commonly used in the early days in ac power suppliers but in recent years it has been replaced by silicon type as it sometimes emit toxic fumes when it burnt out. The characteristic is that it allows current to flow in one direction as shown in the symbol below. It has a cathode and a anode which determine the flow of the current. Current can only flow from anode to cathode.
Silicon V-I characteristics are shown in the figure below. The junction barrier for silicon is about 0.7V and for Germanium is about 0.3V. It is also called forward voltage drop. Most of the diode used today are of silicon type as they are robust and reliable from DC to RF small signal applications.
Types of Commercially Available Diodes
In small signal application of which the current requirement is less than 100mA, 1N4148 is a typical choice. It has a forward voltage drop of 0.7V and is made from Silicon type.
In recifier circuit applications, the typical ones used are 1N4001 to 1N4007 for current rating of 1A and 1N5401-1N5408 for current rating up to 3A. The table below shows the devices and their maximum reverse voltage ratings.
Diode
MaximumCurrent
MaximumReverseVoltage
1N4001
1A
50V
1N4007
1A
1000V
1N5401
3A
100V
1N5408
3A
1000V
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