26/08/2014
Basic Electronic Components:
Bipolar Transistor Basics
In the Diode tutorials we saw that simple diodes are made up from two pieces of semiconductor material, either silicon or germanium to form a simple PN-junction and we also learnt about their properties and characteristics. If we now join together two individual signal diodes back-to-back, this will give us two PN-junctions connected together in series that share a common P or N terminal. The fusion of these two diodes produces a three layer, two junction, three terminal device forming the basis of a Bipolar Junction Transistor, or BJT for short.
Transistors are three terminal active devices made from different semiconductor materials that can act as either an insulator or a conductor by the application of a small signal voltage. The transistor’s ability to change between these two states enables it to have two basic functions: “switching” (digital electronics) or “amplification” (analogue electronics). Then Bipolar Transistors have the ability to operate within three different regions:
• Active Region – the transistor operates as an amplifier and Ic = β.Ib
• Saturation – the transistor is “Fully-ON” operating as a switch and Ic = I(saturation)
• Cut-off – the transistor is “Fully-OFF” operating as a switch and Ic = 0
