Blog 1: Diodes

Diode is a two-terminal electrical device that has its own resistance and conductance.

Diode has many different purposes, it can be used as voltage regulators, switching applications, light emitting, steering diodes, tuning devices, frequency multiplying devices, mixing devices or to make logic decisions in digital circuits.

A semicondutor diode has the following types:

* p-n junction diode

* Light emitting diode (LED)

* Zener diode

* Avalanche diode

* Laser diode

* Thermal diode

* etc...

I will only be talking about two semiconductor diode here which are p-n junction diode and Zener diode due to there are too many different types.

These diodes normally have two terminals which are Anode "A" and Cathode "K".

In most of the diodes, a white or black  painted band is always a Cathode terminal. This is how we identify the terminals of the diodes.

A semiconductor diode is a two terminal component that electron will only be able to flow in one direction: Anode"A" to Cathode "K".

P-N junction diode:

When a p-n junction diode is connected in the forward bias arrangement which is positive to Anode and negative to Cathode, if the voltage exceeds 0.7V the electron will cross the junction and combine with holes so the current will flow. However when the diode is connected in the reverse bias arrangement which is negative to Cathode and positive to Anode, holes get attracted away from the junction so the current will not flow

The Cathode needs to connected towards negative side of the circuit if we want the diode conducting.

This photo shown below is an actual 1N4007 p-n junction diode:

The action of the diode takes place in p-n junction where is the boundary between the two terminals

This photo shown below is the data sheet of the diode:

As we can see, a diode has many characteristics which the main things that we need to notice are:

* Average rectified current

* Power dissipation

* Thermal resistance

* Storage and operating temperature range

* Peak reverse voltage

* etc..

These parameter will change depends on the ambient temperature.

Zener diode:

Zener diode is a kind of semiconductor diode that can be operated to conduct backward which we call zener breakdown. 

When a zener diode is connected in forward bias region, it works as a normal diode. However it works totally different than the normal diode when it connected in the reverse bias region. 

If a normal diode is connected in forward bias region, when the breakdown voltage exceeds, the diode will be destroyed due to overheating, but the zener diode is designed to have a greatly reduced breakdown voltage which will allow current to keep the voltage across the zener diode close to it.

This photo shown below is an actual Zener diode:

The zener diode can be used as voltage regulation or protecting the circuit and etc…

How to check if a diode is bad?

First of all , we will need a multitmeter.Set the multimeter to diode test mode,place one probe from the multimeter on to one of the diodes legs, and the other probe on to the other leg. Write down the reading obtained, and then swap the positions of the probes and write down the new reading.
If we get a reading in one direction indicating the current is bocked or open circuit and a low resistance reading in other direction,then the diode is good.

If we get a open circuit reading from both direction or a low resistance reading in both direction,then the diode is broken and needs to be replaced.

A faulty diode or the diode connected in the wrong direction will cause the circuit either not flowing current which the circuit will not be working or the diode is not working properly as it should which this could blow other components in the circuit and causes huge problems.

References:

auto101.com

wikipedia

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Vijay Naidu