1. TRANSISTOR

2.  A transistor is a semiconductor device used to amplify and switch electronic signals and electrical power.  The transistor is the fundamental building block of modern electronic devices  There are two types of transistors  Bipolar Junction Transistor  Field-effect Transistor

3. Bipolar Junction Transistor  Bipolar junction transistor (BJTs) is made by three doped semiconductor region separated by two pn junctions sown in figure 1.  The term bipolar refers to use both the holes and electrons as carriers in the transistors structure.  There are two types of BJTs  npn (two n-regions separated by a p region)  pnp (two p-regions separated by a n region)

4. Figure-1 Basic BJTs construction

5. BASIC BJTs CONSTRUCTION  The pn-junction joining the base region and emitter region is called base emitter junction  The pn-junction joining the base region and collector region is called base- collector junction  A wire lead is connected to each of three region. These leads are labeled E, B and C for emitter, base and collector respectively as shown in figure-1 (b).  The base region is highly doped as compare to heavily doped emitter and moderately doped collector regions

6. Figure-2 standard BJTs symbols

7. BASIC BJTS OPERATION  Base- emitter junction is forward bias  Base collector junction is reverse bias

8. BJTs Currents and Voltages

9. Voltage across R B is By Ohms law The value of I B is then

10. Voltage at collector Voltage across R C Then the voltage at collector The voltage at reverse bias collector base junction

11. DC Beta(β DC )b The ratio of collector current to base current is the current gain of transistors and is given by Typical values of β DC ranges from 20 to 200.

12. The ratio of collector current to emitter current is the dc α DC and is given by The values of α DC range from 0.95- 0.99 but always less than 1. Dc Alpha (α DC )

13. Problem-1 Determine I B, I C, I E, V BE, V CE, and V CB in the following circuit (β DC = 150)

14. Solution-1

15. Problem-2 Determine I B, I C, I E, V BE, V CE, and V CB for the following circuit values (β DC = 90) R C = 220 Ω R B = 22 k Ω V CC = 9V V BB = 6V Problem-3 Determine values of I E and β DC for a transistor where I C = 3.65 mA I B = 50 µA