1. Bipolar Junction Transistors (BJT) 8/25/2015www.noteshit.com1

2. The Two Types of BJT TransistorsThe Two Types of BJT Transistors npnpnp 8/25/2015www.noteshit.com2

3. BJT Relationships - Equations 8/25/2015www.noteshit.com3

4.  = Common-emitter current gain  = Common-emitter current gain  = Common-base current gain  = IC  = IC  = IC  = IC IB IE IB IE The relationships between the two parameters are:  =   =   =   =   + 1 1 -   + 1 1 -  Note:  and  are sometimes referred to as  dc and  dc because the relationships being dealt with in the BJT are DC. DC  and DC  8/25/2015www.noteshit.com4

5. Modes of Operation 8/25/2015www.noteshit.com5

6. Three Types of BJT Biasing 8/25/2015www.noteshit.com6

7. Electrostatic variables for a pnp BJT at equilibrium 8/25/2015www.noteshit.com7

8. Common-Base Circuit Diagram: NPN Transistor The Table Below 8/25/2015www.noteshit.com8

9. Common-Base Although the Common-Base configuration is not the most common biasing type, it is often helpful in the understanding of how the BJT works. Emitter-Current Curves Saturation Region IEIEIEIE ICICICIC V CB Active Region Cutoff I E = 0 8/25/2015www.noteshit.com9

10. Common-Emitter 8/25/2015www.noteshit.com10

11. Common-Collector 8/25/2015www.noteshit.com11

12. Eber-Moll BJT Model 8/25/2015www.noteshit.com12

13. Common-emitter transistor Common-emitter transistor ampliers are so- called because the input and output voltage points share the emitter lead of the transistor in common with each other, not considering any power supplies. ² Transistors are essentially DC devices: they cannot directly handle voltages or currents that reverse direction. In order to make them work for amplifying AC signals, the input signal must be offset with a DC voltage to keep the transistor in its active mode throughout the entire cycle of the wave. This is called biasing. 8/25/2015www.noteshit.com13

14. Common-collector transistor Common-collector transistor ampliers are so-called because the input and output voltage points share the collector lead of the transistor in common with each other, not considering any power supplies. ² The output voltage on a common-collector amplier will be in phase with the input voltage, making the common- collector a non-inverting amplier circuit. ² The current gain of a common-collector amplier is equal to Ø plus 1. The voltage gain is approximately equal to 1 (in practice, just a little bit less). 8/25/2015www.noteshit.com14

15. Common-base transistor Common-base transistor ampliers are so-called because the input and output voltage points share the base lead of the transistor in common with each other, not considering any power supplies. ² The current gain of a common-base amplier is always less than 1. The voltage gain is a function of input and output resistances, and also the internal resistance of the emitterbase junction, which is subject to change with variations in DC bias voltage. 8/25/2015www.noteshit.com15

16. TRANSISTOR MODEL Common-Base Configuration  Common-base BJT transistor  re model  re equivalent cct. 8/25/2015www.noteshit.com16

17. Therefore, the input impedance, Zi = re that less than 50Ω. For the output impedance, it will be as follows; 8/25/2015www.noteshit.com17

18. The hybrid parameters: hie, hre, hfe, hoe are developed and used to model the transistor. These parameters can be found in a specification sheet for a transistor. Hybrid Equivalent Model 8/25/2015www.noteshit.com18

19. Determination of parameter 8/25/2015www.noteshit.com19

20. General h-Parameters for any Transistor Configuration hi = input resistance hr = reverse transfer voltage ratio (Vi/Vo) hf = forward transfer current ratio (Io/Ii) ho = output conductance 8/25/2015www.noteshit.com20

21. Common emitter hybrid equivalent circuit 8/25/2015www.noteshit.com21

22. Common base hybrid equivalent circuit 8/25/2015www.noteshit.com22

23. Transistor as a Switch 8/25/2015www.noteshit.com23

24. Power Transistor Structure 8/25/2015www.noteshit.com24

25. Switching Characteristics of BJT 8/25/2015www.noteshit.com25