What is Diode ? How Many Types of Diode are used in Mobile phone ?


What is Diode ? How Many Types of Diode are used in Mobile phone ?

What is Diode

What is the Diode ? 

A solid-state device with two electrodes which passes only the electric current of a particular polarity from one side is called a diode. The solid-state diode is generally made of germanium or silicon semiconductor. This is used for rectification and switching.

Many types of diodes are used in electronic devices. Chip diodes arc used in telecommunications (mobile phones etc). These are surface-mount devices (SMD). Surface mount devices are solders with special technique on the track of PCB.

Diode can be briefly described as below :-

Shown with the Character :-  



Graphical Symbol :-  

Diode Symbol

Work :-  Making AC to DC ( Converting)
Unit :- Diode, Connected in the mobile, first identify with code and then connected in the mobile
Structure :-


The components made of a combination of P-type and n-type semiconductors are called diodes. It is also called P-N junction diode

         P-type part of the diode is called Anode and N-type part is called Cathode. The point where both where these two sides combine, is called depletion layer because in this section, the electrons and holes remain neutral and do not attract each other. Due to this depletion layer, the electrons from either sides can not unite.


Working system of diode

The voltage required to activate a diode is called diode bias. This biasing are of two types:

  1. Forward biasing
  2. Reverse biasing

(I) Forward biasing:-

    When positive supply is given on the anode and negative to the cathode, it is called forward biasing. The diagram below illustrates forward biasing.

Positive terminal of the battery has been connected with anode and the negative terminal is connected with cathode. This results in to formation of ‘hole’ in anode (p-area) of diode and pressure is created on cathode (N-area) because equal charges repel each other. As the pressure continues to increase, resistance of the depletion layer (junction) decreases to zero and the current flow starts


(ii) Reverse biasing:-

      Supply of negative to anode (P) terminal and positive to cathode (N) terminal is called reverse biasing. The circuit diagram given below illustrates reverse biasing.

Positive terminal of battery has been connected with cathode of diode and the negative terminal with the anode. As a result the ‘holes’ of anode of the diode attract the electrons of battery and the positive terminal of the battery attracts the electrons of the cathode and the resistance of depletion layer goes on increasing and stops the flow of current.


Mostly AC is used for electrical energy, but in some cases, DC has to be used. The process of conversion of AC to DC is called rectification.

Signal diode

This type of diode is used to detect signals. These diodes are made of glass. A red ring on the terminal marks its cathode. These diodes are available in following numbers. IN4148, IN34, 0A79 etc. The SMD signal diode is also available in black.

Zener Diode

It is a special type of diode made of silicon that is used to keep the output supply stable. Zener diodes are used to stabilize the voltage. Zener diodes are represented by “Z”

Working System

       There is an increase in depletion layer when reverse bising is given on biasing of diode. The depletion layer in zener diode also increases when reverse biasing is given. In spite of that some leaked current flows and the leakage current increases with the increase of reverse voltage. The flow of current suddenly increases after a definite reverse voltage. This reverse voltage is called “breakdown voltage or “genre volt”. The suddenly increased current is called reverse current.

      When forward bias is given to the zener diode, then it works like as a general diode. Zener diode is identified by its “Zener volts” such as 3.0VZ, 3.9VZ, 5.1VZ, 6.2VZ etc.

Varacter Diode

      It is a capacitance diode that operates on the principle of variable capacitor. You have already learned in capacitor chapter, that when capacitance can be increased or decreased by varying the distance between both the plates. This diode also works on the same principle. Reverse biasing is given to varacter diode for using it. Depletion layer increases or decreases on the basis on reverse voltage given to it. On the basis of this the diode functions within a defined range of capacity. Varacter diodes are available in the values ranging from 1 to 500 pf and 10 to 100V (working volt) values are available. These are used in the signal transmission circuits.

Tunnel Diode

This diode possessing the properties of negative resistance, and are used for switching at microwave frequency level, is called tunnel diode.

SMD LED (Light Emitting Diode)

This type of LED is used to en light the display or keypad in mobile phones. LED is available in many colors. It produces light after receiving forward biasing.

Testing of Diode

There is a separate range in digital multi meter, for checking diode. For checking any diode by multi meter, first of all the selector know is selected at this range. Subsequently black probe of the multi meter is connected with common plug and the red probe is connected with VQ. When the other ends of the probe is placed in one direction, the screen displays low, and high on the other side of the resistance. If this happens, it means that the diode is ok. If low is indicated both the times, it indicates that the diode is short and if both times the display shows high or no display at all, it means the diode is open.




My name is Rajkishor Sharma, I am a mobile phone Repair technician and software expert. I specialized in mobile phone software & hardware. I love to share my knowledge, solutions, tips, and tricks regarding mobile phones.

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