1. MALVINO
Electronic
PRINCIPLES
SIXTH EDITION

2. Bipolar Transistors
Chapter 6

3. N P N The bipolar junction transistor has 3 doped regions.
COLLECTOR (medium doping) P
BASE (light doping) N
EMITTER (heavy doping)

4. In a properly biased NPN transistor, the emitter electrons
diffuse into the base and then go on to the collector. RC N
VCE RB P
VCC N
VBE
VBB

5. IC IB IE IC IB IE
Conventional flow
Electron flow
IE = IC + IB IE
IB << IC
adc = IC IE
bdc = IC IB

6. RC RB VCE VCC VBE VBB The common emitter connection has two loops:
the base loop and the collector loop. RC RB
VCE
VCC
VBE
VBB

7. Subscript notation
When the subscripts are the same, the voltage represents a source (VCC).
When the subscripts are different, the voltage is between two points (VCE).
Single subscripts are used for node voltages with ground serving as the reference (VC).

8. The base circuit is usually analyzed with the
same approximation used for diodes.
VBB - VBE RC
IB = RB
VCE
VCC RB
VBE
VBB

9. A graph of IC versus VCE 100 mA 14 12 80 mA 10 60 mA IC in mA 8 40 mA
(Note that each new value of IB presents a new curve.)
100 mA 14 12
80 mA 10
60 mA
IC in mA 8
40 mA 6 4
20 mA 2
0 mA 2 4 6 8 10 12 14 16 18
VCE in Volts
This set of curves is also called a family of curves.

10. Regions of operation Cutoff - - - used in switching applications
Active used for linear amplification
Saturation used in switching applications
Breakdown can destroy the transistor

11. Transistor circuit approximations
First: treat the base-emitter diode as ideal and use bIB to determine IC.
Second: correct for VBE and use bIB to determine IC.
Third (and higher): correct for bulk resistance and other effects. Usually accomplished by computer simulation.

12. The second approximation:
VBE = 0.7 V
bdcIB
VCE

13. IB =
VBB - VBE RB
5 V V
IB =
= 43 mA RC
100 kW
100 kW
VCC RB
VBE = 0.7 V
VBB
5 V

14. IC = bdc IB
IC = 100 x 43 mA = 4.3 mA RC
100 kW
bdc = 100
VCC RB
IB = 43 mA
VBB
5 V

15. VRC = IC x RC
VRC = 4.3 mA x 1 kW = 4.3 V
1 kW RC
IC = 4.3 mA
100 kW
12 V
VCC RB
IB = 43 mA
VBB
5 V

16. IC = 4.3 mA
VCE = VCC - VRC
VCE = 12 V V = 7.7 V
1 kW RC
VCE
100 kW
12 V
VCC RB
IB = 43 mA
VBB
5 V

17. Typical Breakdown Ratings
VCB = 60 V
VCEO = 40 V
VEB = V
Note: these are reverse breakdown ratings

18. A graphic view of collector breakdown14 12 10
IC in mA 8 6 4 2 50
VCE in Volts

19. Typical Maximum Ratings
IC = mA dc
PD = 250 mW (for TA = 60 oC)
PD = 350 mW (for TA = 25 oC)
PD = 1 W (for TC = 60 oC)

20. Typical “On Characteristics”
IC in mA hFE(min) hFE(max)
___
___
___
___

21. Troubleshooting Look for gross voltage errors.
First approximation and mental estimates will usually suffice.
Resistors don’t short but circuit boards can.
Circuit boards can and do open.
Junctions can and do short.
Junctions can and do open.