1. BY: Sai Kiran Reddy Dwarampudi
TRANSISTOR
BY: Sai Kiran Reddy
Dwarampudi

2. Recall p-n junction P N W + - Vappl < 0 Vappl > 0 I I V V
Forward bias, + on P, - on N
(Shrink W, Vbi)
Allow holes to jump over barrier
into N region as minority carriers
Reverse bias, + on N, - on P
(Expand W, Vbi)
Remove holes and electrons away
from depletion region I V I V

3. Transistor Trans—relation b/w input and output
Istor—is taken from the RESISTOR
Output resistance by input
resistance

4. Origin of the names
the Emitter 'emits' the electrons which pass through the device
the Collector 'collects' them again once they've passed through the Base
...and the Base?...

6. Currents

7. Conventional View

9. types
Bc driver stage
2n2222--switching
Bc547
Bc548

10. CONFIGURATIONS
COMMON BASE
COMMON COLLECTOR
COMMON EMITTER

11. Common Base NPN

12. Common Collector NPN How does IC vary with VCE for various IB?
Note that both dc sources are variable
Set VBB to establish a certain IB

13. Common Emitter NPN

14. Common Emitter Characteristics
We can therefore draw an input characteristic (plotting base current IB against base-emitter voltage VBE) and
an output characteristic (plotting collector current Ic against collector-emitter voltage VCE)

15. IDEAL CE INPUT (Base) Characteristics

16. IDEAL CE OUTPUT (Collector) Characteristics

17. ACTUAL CE OUTPUT Characteristics
IB =

18. Various Regions (Modes) of Operation of BJT
Active:
Most important mode of operation
Central to amplifier operation
The region where current curves are practically flat
Saturation:
Barrier potential of the junctions cancel each other out causing a virtual short (behaves as on state Switch)
Cutoff:
Current reduced to zero
Ideal transistor behaves like an open switch
* Note: There is also a mode of operation called inverse active mode, but it is rarely used.

19. DC  and DC   = Common-emitter current gain
 = Common-base current gain
 = IC  = IC
IB IE
The relationships between the two parameters are:
 =   = 
 
Note:  and  are sometimes referred to as dc and dc because the relationships being dealt with in the BJT are DC.

20. The DC Operating Point
For a transistor circuit to amplify it must be properly biased with dc voltages. The dc operating point between saturation and cutoff is called the Q-point. The goal is to set the Q-point such that that it does not go into saturation or cutoff when an a ac signal is applied.
Fig 5-2a & Fig 5-4

21. NEED FOR STABLIZING Q-POINT
Ambience temperature
Human Error
Cut-in voltage [ -2.5mv/c]
STABILITY FACTOR: Measure of stability of operating point

22. biasing Fixed bias Collector to base bias
Fixed bias with emitter resistor
Self bias or voltage divider bias

23. Fixed Bias

24. Collector to base bias

25. Emitter Bias

26. Self bias

27. Transistors as Switches