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Diodes that as used with signal lines, that means the current flowing through them is very small are known as signal diodes. They have very low current rating. 1N4148 is a very common signal diode which has VF of 0.72V and maximum forward current of 300mA.

Other types of diodes that are used in power lines are know as power diodes or rectifier diodes. They have much higher forward current rating like 1A 3A 6A etc. Mainly they are used as rectifier (convert AC to DC). Most common ones are 1N400x series. Like the 1N4007 which has a forward current rating of 1A.

Light Emitting Diodes

They require an article on their own, but here I would just like to say that they emit light when a forward voltage is applied. They comes in transparent or semitransparent case. Its very tough to show how they look because their are too many different types of LEDs because of extremely widespread use. Any indicator light on your laptop, monitor, keyboard are LED only ! Backlight of mobile phones are LED. High quality PC screens and sTVs have LEDs for their backlight. Now a days even streets, home and offices are using them in place of CFLs. They are available in many different colours.

5mm red led round type
5mm green led round type
5mm red led round type
Any colour
Diffused Colour Type Body
Clear Type Body
Fig. 5mm Round Type LEDs

The picture above show round type leds with 5mm diameters. They are also available in other shapes like rectangle. Round type leds are also available in smaller or bigger diameters like 3mm or 8mm.

Special type of LEDs are also available that emit light that cannot be seen by human eyes like infrared LEDs. They are used in the remote controls of your TV (and many other devices) to send data wirelessly.

LEDs are also widely used for display purpose that means to show numerical or textual output to user. You must have seen an electronic weighing scale, it displays the weight using these leds.

seven segment display green
seven segment display red
led dot matrix display
Seven Segment Display (Can show numbers only)
A 5x7 Dot Matrix Display
Fig. LED Displays

Schematic symbol for LED
Fig. Schematic Symbol for LED

Zener Diodes

zener diodes and their circuit symbol
Fig. Zener Diode

While most other diodes are used in forward bias condition, zeners are used in reverse. Zeners generally have a very small breakdown voltage (say 3.3v). But they have the ability to hold the voltage exactly at their zener voltage. So they are used to create a know voltage reference. Zener diodes are available in many different zener voltages like 3.6v, 5.1v etc.

For example say if you have two circuits that have different operating voltage. Let's assume circuit A works on 5v but circuit B works on 3.3v. Now the problem is that you want to send a signal from circuit A to circuit B. In digital electronics data is transferred in binary. In binary their are only two states HIGH and LOW. If circuit A want to send HIGH it will pull the signal line to 5v, but you cannot use this as an input to circuit B because for circuit B HIGH is 3.3v. So you can use a zener diode with breakdown voltage of 3.3v to convert 5v from circuit A to 3.3v.

working of zener diodes
Fig. Zener Diode Usage


A photo diode is the reverse of LED, that means it generate some electrical current when light falls on them. They are used in optical fiber communication.

schematic symbol for photodiode
Fig. A Photo Diode

Schottky Diode

They have much lower forward voltage drop compared to other diodes.

Schottky Diode Symbol
Fig. A Schottky Diode

There are lots more type of diode but our aim here is NOT to write a boring book, but to create a guide that introduce you to diodes. It is due to this reason we are keeping the list as small as possible.

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