1. Bipolar Junction Transistors (BJTs)

2. Types of BJTs  NPN  PNP

3. NPN-BJT Structure n-type p-type n-type

4. NPN BJT Symbol E B C

5. PNP-BJT Structure p-type n-type p-type

6. PNP BJT Symbol  Emitter is reversed E B C

7. Current Flow Convention E Emitter (n-type) Base (p-type) Collector (n-type) B C IEIE IBIB ICIC

8.  WORKING

9. BJT structure note: this is a current of electrons (npn case) and so the conventional current flows from collector to emitter.

10. Transistor Connections  Common Base Connection  Common Collector Connection  Common Emitter Conncetion

11. Common Base Connection

12.  Current Amplification Factor α =I C / I E ( constant V CB ) The value of α is lies b/w 0.9 to 0.999 Total collector current I C =αI E +I leakage

13. Common Collector Connection

14.  Current Amplification Factor γ = I E /I B Expression for collector current. I C = I B /1-α + I CBO /1-α

15. Common Emitter Conncetion

16.  Base Current Amplification Factor β= I C / I B The range of β is 20 to 500. Expression for collector current. I C = βI B + I CEO