Bipolar Junction Transistor (BJT)

Transistors has at least 3 terminalsis. Voltage/Current to one pair of the terminal changes the current flowing through the other pair of terminals thus used for amplifying or switching electronic signals. 


Bipolar Junction Transistor (BJT)

Not Pointing iN (NPN)  Point iN Please (PNP) 

Bipolar
-high voltage gain
-low current gain
-low input impedance
-low output impedance
-medium noise generation
-medium switching time
-robust
-requires zero input to turn it "OFF"
-current controlled device
-cheap



BJT as a switch.
To work out RB in this type of circuit

Calculate the the resistor needed for Rb
If Vcc=14, VBB = 5 volts, Rc=150,Beta= 55, Vce= .5 volts


We first need to get Ic, this is done by dividing Vsupply (Vcc) by Rc, do not forget to minus Vce 
So:Ic= (Vs-Vce)/Rc
Then we use the beta formula : Ic=Beta x Ib,
 we to transpose this formula to get Ib
Once we have Ib we can use it to calculate Rb by dividing VBB by Ib, do not forget to minus Vbe :
Rb=(VBB-Vbe)/Ib


Ic=(14-0.5)/0.09
Ic=0.09A


Ib=0.09/55
Ib=0.00163A


Rb=(5-0.7)/0.00163
Rb=2638 use 2700




Fault finding a BJT