1. Transistors
Electronics 1
CVSD

2. Transistor History First developed in 1948 at Bell Laboratories
Originally called Transfer Resistor TRANSISTOR

3. Transistor History
Drastically changed the field of electronics to how we think of electronics today.
MINIATURIZATION!!!
Replaced the vacuum tube

4. Semi-Conductor Diode Review
Doping:
P- Type material = Hole Movement (Depletion of Electrons)
N- Type material = Carrier Movement (Excess of Electrons)
Diodes have one PN junction

5. Semi-Conductor Diode Review
Biasing:
Forward Bias = Anode is more positive than Cathode
Reverse Bias = Cathode is more positive than Anode
Voltage must be high enough to overcome depletion region (Forward Operating Voltage)

6. Semi-Conductor Diode Review
Elements Commonly used In Semi-conductors:
Silicon:
Forward Bias Voltage Drop of ~ .6 volts
Germanium:
Forward Bias Voltage Drop of ~ .3 volts
HEAT SINK ALL SEMI-CONDUCTORS!

7. Bipolar Junction Transistors (BJT)

8. Bipolar Junction Transistors Advantages Of Transistors Over Vacuum Tubes
Much- Smaller And Lighter
Consume Much less Power
Do Not Get Hot
More rugged – No Glass to Break
No Warm Up Time Needed

9. Bipolar Junction Transistors Disadvantages Of Transistors Over Vacuum Tubes
Can Not Handle Same Amount of Power
Sensitive To Temperature and Radiation
Harder To Mass Produce

10. Bipolar Junction Transistors Types of BJTs
NPN
PNP
Type is determined by one type of semi-conducting material sandwiched in between two other semi-conducting materials that are both alike.
Called “Bipolar” because both holes & electrons take part in current flow

11. Transistor Types

12. Bipolar Junction Transistors
Because there are two junctions, transistors are generally labeled with the prefix “ 2N”:
2N3904
2N3906
2N2222
2N2907

13. Bipolar Junction Transistors Schematic Symbols
“Not Pointing In”
NPN
PNP

14. Bipolar Junction Transistors Terminals
Collector
Base
Emitter

15. Bipolar Junction Transistors Terminals
3904
Emitter
Collector
Base

16. Bipolar Junction Transistors Terminals
Base
Emitter
Collector

17. Bipolar Junction Transistors Bias
Base
Used to control amount of collector current flow
Changes the “resistance” of the transistor (E to C)
Base-Emitter Junction
Must be Forward Biased!
Base-Collector Junction
Must Be Reverse Biased!

18. Bipolar Junction Transistors NPN Junction Polarity
Two Diodes “Anode to Anode”

19. Bipolar Junction Transistors NPN Current Flow

20. Bipolar Junction Transistors PNP Junction Polarity
Two Diodes “Cathode to Cathode”

21. Bipolar Junction Transistors PNP Current Flow

22. Transistor Specifications
Current Gain
Cutoff
Saturation

23. Transistor Specifications Current Gain
Definition:
The ratio of base current to the collector current.
Also referred to as Beta (β)
Expresses how much the transistor is amplifying an input.

24. Transistor Specifications Current Gain
Formula:
Typical Gain ~ 100
Does not have any unit since it is simply a ratio

25. Current Gain Practice β = (Ic) / (Ib) β = 70mA (.07A) / .5mA (.0005A)
Ib (E-B Current) - .5mA
Ic (E-C Current) – 70mA
β = (Ic) / (Ib)
β = 70mA (.07A) / .5mA (.0005A)
β = 140

26. Transistor Specifications Current Gain
Because current flows from emitter to base and emitter to collector, the relationship of these currents are:
IE = IC + IB

28. Transistor Specifications Cutoff
Definition:
Transistor is NOT conducting (No current flow)
Occurs when the base emitter junction is allowed to become reverse biased.

29. Transistor Specifications Saturation
Definition:
Although the transistor is active (current flow from E to C), it is the point where any increase in base current produces no further collector current gain.

30. Transistor Applications
Switching
Amplification

31. Transistor Applications
Flasher

32. Transistor Applications
Moisture Meter

33. Review Transistors replaced what component: BJT stands for:
Draw and label the symbols for a PNP and NPN transistor
What is current Gain
What is Cutoff
What is Saturation
What can Transistors be used for
What would be the current gain for a transistor with a E-B current of .6mA and a E-C current of 40mA