types of diode

Type of Diode - Simple  

 

Introduction

Diodes are electronic components functions as a one-way valve it means it allow 

current to flow in one direction. These diodes are manufactured by the semiconductor 

materials germanium, silicon and selenium. Operation of diode can be classified in two 

ways, if it allows the current then it is forward biased otherwise it is reverse biased.

1. Small Signal Diode

It is a small device with disproportional characteristics and whose applications are 

mainly involved at high frequency and very low currents devices such as radios and 

televisions etc. To protect the diode from contamination it is enveloped with a glass so

 it is also named as Glass Passivated Diode which is extensively used as 1N4148. 

The appearance of signal diode is very small when compared with the power diode. To 

indicate the cathode terminal one edge is marked with black or red in color. For the 

applications at high frequencies the performance of the small signal diode is very 

effective.

With respect to the functional frequencies of the signal diode the carrying capacity of 

the current and power are very low which are maximum nearly at 150mA and 500mW.

The signal diode is a silicon doped semiconductor diode or a germanium doped diode 

but depending up on the doping material the characteristics of the diode varies. In 

signal diode the characteristics of the silicon doped diode is approximately opposite 

to the germanium doped diode.

The silicon signal diode has high voltage drop at the coupling about 0.6 to 0.7 volts so, it has very 

high resistance but low forward resistance. On other hand germanium signal diode has low resistance 

due to low voltage drop nearly at 0.2 to 0.3 volts and high forward resistance. Due to small signal the 

functional point is not disrupted in small signal diode.

2. Large Signal Diode

These diodes have large PN junction layer. Thus the transformation of AC to DC 

voltages is unbounded. This also increases the current forward capacity and reverse 

blocking voltage. These large signals will disrupt the functional point also. Due to 

this it is not suitable for high frequency applications.

The main applications of these diodes are in battery charging devices like inverters.

In these diodes the range of forward resistance is in Ohms and the reverse blocking 

resistance is in mega Ohms. Since it has high current and voltage performance these 

can be used in electrical devices which are used to suppress high peak voltages.

3.  Zener Diode

It is a passive element works under the principle of zener breakdown. 

First produced by  Clarence zener in 1934.It is similar to normal diode in forward  

direction, it also allows 

current in reverse direction when the applied voltage reaches the breakdown voltage.

 It is designed to prevent the other semiconductor devices from momentary voltage 

pulses. It acts as voltage regulator.

4. Light Emitting Diode (LED)

These diodes convert the electrical energy in to light energy. 

First production started in 1968. It undergoes electroluminescence process in which 

holes and electrons are recombined to produce energy in the form of light in forward 

bias condition.

Earlier they used in inductor lamps but now in recent applications they are using in 

environmental and task handling. Mostly used in applications like aviation lighting, 

traffic signals, camera flashes.

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5. Constant Current Diodes

It is also known as current-regulating diode or constant current diode or current-

limiting diode or diode-connected transistor. The function of the diode is regulating 

the voltage at a particular current.

It functions as a two terminal current limiter. In this JFET acts as current limiter to 

achieve high output impedance. The constant current diode symbol is shown below.

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