TRANSISTOR

different transistors

Transistor is perhaps the most important of electronic components because of which all modern electronics works. A transistor is a semiconductor device commonly used to amplify or switch electronic signals. It’s a Device with three terminals where one terminal can be use to control the flow of current through the other two terminals. The three terminals are Emitter, Base and Collector. Its major use is as amplifier to boost various signals as well as to perform automatic switching.

There are 2 types of transistors

NPN

NPN Symbol

 

When base of n-p-n is connected with logic high voltage (positive voltage) then it short circuits emitter and collector (SWITCH ON). When base of n-p-n is connected with logic low voltage (Ground of Supply) then it open circuits both emitter and collector (SWITCH OFF).

PNP

PNP symbol

When base of p-n-p is connected with logic high voltage then it opens circuit’s emitter and collector (SWITCH OFF). When base of p-n-p is connected with logic low voltage then it short circuits both emitter and collector (SWITCH ON).

Another point you should keep in mind is that the arrow always points in the direction of positive charge flow, or from the P to N sections, no matter whether the P section is the emitter or base.

Notation aside, the three pins – base, emitter, collector – are typically labeled on the data sheet for a transistor

Connection for N-P-N transistor

NPN switch

  • Device power to whatever power source I want to use
  • Device ground to the collector on my NPN transistor
  • Transistor emitter to “real” ground.

 

Connection for PNP transistor

pnp switch

 

 

Example of Transistor with Buzzer

 buzzer example

 

Commonly used Transistors and their pin identifications

Transistor Name Type Picture
BC548/BC547 NPN BC548
BC557 PNP  BC557
2N3904 NPN  2N3904
SL100 NPN  SL100