Bipolar Junction Transistor : (Transistor Configurations (CB: the base is…
Bipolar Junction Transistor :
Definition: a semiconductor device with three connections, capable of amplification in addition to rectification.
How does it work?
The emitter “emits” electrons into the base, Most of the electrons emitted are “collected” by the collector, which sends them along to the next part of the circuit.
CB: the base is made common to the emitter and collector of the transistor.
CC: the collector os made common to the base and emitter of the transistor.
CE: the emitter is made common to the base and the collector of the transistor.
Current gain: hFE = Ic/ Ib
Current equation: Ie = Ic + Ib
Transistor as a switch
When a transistor operates as a switch, it is either ON (current flowing), or OFF (no current), thus enabling it to switch other electronic devices ON and OFF.
When the switch is closed
a small current flows into the base (B) of the
transistor, which is just enough to make LED B glow dimly.
When the switch is open,
no base current flows, so the transistor switches off the collector current. Both LEDs are thus off.
The degree of amplification is usually measured by the DC current gain, hFE.
Transistor as an amplifier
A simple application would be to increase the level of the signal received
from low current devices and turn on high current devices, such as motors.
Amplification is the process of increasing the level of a weak signal.
A small change in the base current of a transistor produces a large variation in the collector current as shown. Therefore it could be used as an amplifier.