|
|
| Transistor |
|
|
When a third doped element is added to a crystal diode in such a way that two pn junctions are formed, the resulting device is called transistor. |
|
|
Invented in 1948 by J. Bardeen and W.H. Brattain of bell telephone laboratories USA, transistor has now become the heart of most electronic applications. |
|
|
A transistor consists of two pn junction formed by sandwiching either p-type or n-type semiconductor between a pair of opposite types.
|
|
|
Accordingly, there are two types of transistors namely: n-p-n transistor and p-n-p transistor |
|
 |
|
(i) |
|
|
An n-p-n transistor is composed of two n-type semiconductors separated by a thin section of p-type as shown in figure (i).
|
|
 |
|
(ii) |
|
|
A p-n-p transistor is formed by two p-sections separated by a thin section of n-type as shown in figure (ii). |
|
|
In each type of transistor, following points may be noted :
|
|
There are two pn junctions. Therefore, a transistor may be regarded as a combination of two diodes connected back to back.
|
|
There are three terminals, taken from each type of semiconductor.
|
|
The middle section is very thin layer. This is the most important factor in the function of a transistor.
|
|
