Thursday, 19 October 2017

What is a Diode?

Rectifiers are the device which converts AC(Alternating Current) int0 Direct Current.The conversion requires a device which can perform those operations are called Power Diodes.
                                          
The example of a rectifier is Power Diode which allows current in one direction only from its anode to cathode(forward direction) and blocks in the backward direction due to its semiconductive properties.
Rectifiers are the device which converts AC(Alternating Current) int0 Direct Current.The conversion requires a device which can perform those operations are called Power Diodes.
The example of a rectifier is Power Diode which allows current in one direction only from its anode to cathode(forward direction) and blocks in the backward direction due to its semiconductive properties.

The Diode is made of Silicon or Germanium; P and N-type were made by adding impurities to the silicon which will be either trivalent or Pentavalent element.
The Process of adding impurities to the semiconductor is known as Dopping.
If the applied voltage more than the barrier voltage of the Diode then the diode will conduct in the backward direction also.
From the above Fig, we can see that the battery Positive is connected to the  Anode and Negative is connected to the Cathode, The P side of the Diode is rich in holes and deficit in electrons Vice versa for N Side. Before applying any voltage Depletion layer will form between P and N Sides due to Thermal excitation.
UnBiased Condition:
Before applying any voltage Depletion layer will form between P and N Sides due to Thermal excitation.The thermal excitation influence the holes movement from P side to the N side and electrons movement from N side to P side.The holes will recombine with the electrons in the N side and the electrons will combine with the holes in the P side this effect creates an immovable region in which all the movement of electrons and holes are seized.This process is called diffusion. The P side will have immovable -ion and N side will have +ve immovable ion which causes static electric field in the depletion region.
                                        
Forward Biased Condition:

When the Diode is forward biased; the Positive end of the battery connected to the P side( Anode) and the Negative terminal of the battery connected to the N side of the diode(cathode), is the movement of electrons, causes the flow of current in the diode but there is a depletion region in the diode(P-N Junction) where there are no any free electrons but when we apply an external voltage then the voltage is higher than the barrier voltage the diode will conduct.
The Barrier Voltage of the Silicon Semiconductor is 0.7V and for Germanium is 0.3V,  Assume the Voltage of the external Source is 0V; Unless until the forward Voltage to the diode reaches 0.7V the diode won’t conduct any current.When the Forward Voltage of the diode is more than the barrier voltage then only the diode will start conducting current.The time taken to overcome the barrier voltage of the diode is known as the Recovery Time.
Reverse Biased Condition:
When the Diode is Reverse Biased; Positive terminal of the battery or source is connected to the cathode or N side of the diode and the Negative terminal of the Battery is connected to the P-Side of the Diode or Anode then the Depletion Zone become much wider that no current will flow, but actually a small amount of current will still flow from N type to P type that’s due to the minority charge carriers.


 The Diodes maximum reverse biased voltage without breakdown is known as Peak Inverse Voltage (PIV), if we keep on increasing the reverse voltage then at one stage the depletion region will be destroyed due to the flow of huge reverse current; the Diode also will get destroyed permanently.This breakdown is known as Avalanche Breakdown.The PIV is linked with the temperature also as Temperature increases the PIV increases and vice versa.
Avalanche BreakDown: When the applied reverse voltage is higher than the breakdown voltage than the depletion region will get destroyed then due to higher potential the free electrons get energised with kinetic energy kicks the atoms of the device to accumulate more electrons by breaking the covalent bonds, thus the accumulation of huge electrons causes the flow of huge current then the Diode will get destroyed eventually.