DIODE AND TRANSISTOR

on Monday, 30 September 2013
In our previous posts we have seen Resistor and its color coding, Capacitor and finding its value, in this post we will look at Diode and Transistor.

DIODE: Diode is a two terminal device which helps the current to flow in one direction i.e zero resistance(ideally) in that direction, and high resistance(infinite ideally) in other direction.
How it looks:
diode
 Look at one end which is coated with silver color, it is the -ve terminal of the diode and remaining one is the +ve terminal.




Symbol:
diode symbol
Look at the symbol beside in which --l> shows that flow of electrons in that direction during forward bias and |-- shows it halts(stops) the flow of electrons if it is reverse bias.







Its clear to us except forward and reverse bias. Yes, we will know what actually mean by forward bias and reverse bias is about...
I will not go in depth to explain forward bias and reverse bias with the fermi levels and all that, but just in lay man way.

Forward Bias: 

forward bias
If the positive terminal of the diode(p type) is connected to the +ve side of the battery and -ve terminal(N type) of the diode is connected to the -ve side of the battery then it is called forward bias.


Reverse Bias:
reverse bias
If the positive terminal of the diode(p type) is connected to the -ve side of the battery and -ve terminal(N type) of the diode is connected to the +ve side of the battery then it is called Reverse bias.



TRANSISTOR: Transistor is a three terminal device which is most useful component in electronics, which is used to amplify signal or acts like a switch.
How it looks:
transistor
 Image shown beside is one type of transistor, you will find many variants depending upon its type.





Transistors are of different types, if i start explaining each of them this whole blog will not be enough. So, i will only deal with basic most frequently used type of transistor i.e BJT (Bipolar Junction Transistor) type.

Bipolar Junction Transistor(BJT) have three terminals Emitter, Base and Collector. BJT is divided into two types
  1. NPN Transistor
  2. PNP Transistor
1.NPN TRANSISTOR: From its name we can easily say that Emitter is of N-type , Base is of P-type and Collector is of N-type. Look at the symbol below


npn
NPN transistor will be ON i.e current flows from Collector to Emitter when base is 'high' relative to emitter.

2.PNP TRANSISTOR: Emitter and Collector is of P-type and Base is of N-type.

pnp
PNP transistor will be ON i.e current flows from Collector to Emitter when base is 'low' relative to emitter.

How to find the Emitter , Base and Collector terminals of the Transistor:
Look at the video below to identify the pins of the transistor and its type.




AUTHOR: YOUSTRON SIC

3 comments:

Nithan said...

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