1. Tim Sumner, Imperial College, Rm: 1009, x47552
Transistors
12/11/2018
Tim Sumner, Imperial College, Rm: 1009, x47552

2. Review : What is a Transistor ?
Collector
NPN Transistor Rules:
VC > VE
VB = VE Volts
I C = I B  
IC : Collector
Current
Base
IB : Base Current
IE : Emitter
Current
I E = I C + I B 
I E = (1 + ) I B
Emitter
FOR MORE INFO...
Relevant Books: Art of Electronics + Lab: Harowitz and Hill
Electronic Circuits: E.C. Lowenberg, SCHAUM SERIES
Electric Circuits: J.A. EDMINISTER SCHAUM SERIES
12/11/2018
Tim Sumner, Imperial College, Rm: 1009, x47552

3. Some Transistor Applications I
+ V
Current Source
Follower:
+ V
Load IC
Vin IC
Vin= 5.6 V
Vout= Vin+ 0.6 Volts
Vout= 5.0 V IE
R = 5 K
IE = 1 mA
- V
12/11/2018
Tim Sumner, Imperial College, Rm: 1009, x47552

4. Some Transistor Applications II
Push-Pull :
Common Emitter Amplifier :
+ V
+ V
RC >> Vout >>
Qup
Vout
Vin = VB
Vin = VE
RE <<  IE = IC >>
Qdown
- V
12/11/2018
Tim Sumner, Imperial College, Rm: 1009, x47552

5. Tim Sumner, Imperial College, Rm: 1009, x47552
The Emitter Follower I
Given : Vcc = 15 Volts
Ic = 0.5 mA;  = 100
f(100 Hz) = 3 db
What about C1 ?
Vcc
Source R1 Ic
Load C1
1F
10 K ~
4.7 K R2 R3
Rbase= VB/IB = 1.64 M
(2) RTH(divider) = 1/10 RB 
RB = 164 K 
R1 = R2= 328 K
(1) R3=7.5 V/0.5 mA = 15K
12/11/2018
Tim Sumner, Imperial College, Rm: 1009, x47552

6. The Emitter Follower II
(3) Think of an RC filter (high-pass) .
15K is parallel to 4.7 K and the whole think times 
 358 K ; parallel with 328 K 
112 K; So f=(1/2RC)  F
Vcc
Source
328 K Ic
Load C1
1F
10 K ~
4.7 K
328K
15 K
 = 100
f(100 Hz) = 3 db
12/11/2018
Tim Sumner, Imperial College, Rm: 1009, x47552

7. Emitter Follower (a bit diff.)
Rin=Rload(1+)
Rout=Rsource/(1+)
12/11/2018
Tim Sumner, Imperial College, Rm: 1009, x47552

8. Common Emitter Amplifier
Gain = R5/R2
Rout=R5
12/11/2018
Tim Sumner, Imperial College, Rm: 1009, x47552

9. Common Emitter Amplifier II
12/11/2018
Tim Sumner, Imperial College, Rm: 1009, x47552

10. The Ebers-Moll Model for BJT
12/11/2018
Tim Sumner, Imperial College, Rm: 1009, x47552

11. Tim Sumner, Imperial College, Rm: 1009, x47552
Temperature Effects
12/11/2018
Tim Sumner, Imperial College, Rm: 1009, x47552

12. Temperature Effects and Current Mirrors
12/11/2018
Tim Sumner, Imperial College, Rm: 1009, x47552

13. Tim Sumner, Imperial College, Rm: 1009, x47552
Exercises
Make a Current Source using a transistor
Make common emitter follower
Make a Common Emitter Amplifier
12/11/2018
Tim Sumner, Imperial College, Rm: 1009, x47552

14. Making Gates using Transistors I
+5 Volts
InPut A
A .OR. B
InPut B
12/11/2018
Tim Sumner, Imperial College, Rm: 1009, x47552

15. Making Gates using Transistors II
InPut A
A .OR. B
InPut B A
OUT 1
Here is what we have made
12/11/2018
Tim Sumner, Imperial College, Rm: 1009, x47552

16. Exercise I Design and construct an AND gate
using transistors and resistors :
InPut A
A .AND. B
InPut B A
OUT 1
The AND gate TRUTH table
12/11/2018
Tim Sumner, Imperial College, Rm: 1009, x47552

17. Tim Sumner, Imperial College, Rm: 1009, x47552
Exercise I continued
Verify the truth table ! You can set an input to ‘1’ by connecting it to +5 V by a resistor of 1K and you set it to ‘0’ by grounding it.
5 V
‘0’
InPut B
‘0’
A .AND. B
InPut A
‘1’
5 V
12/11/2018
Tim Sumner, Imperial College, Rm: 1009, x47552

18. Answer (almost): TTL CMOS
Not quite because this is a NAND gate but we do know
by now how to invert using a transistor
12/11/2018
Tim Sumner, Imperial College, Rm: 1009, x47552

19. Tim Sumner, Imperial College, Rm: 1009, x47552
Important conclusion
You may understand by now that the inputs have no ability to set signals high or low. In contrast to this the outputs can drive signals to
High or Low
12/11/2018
Tim Sumner, Imperial College, Rm: 1009, x47552

20. Tim Sumner, Imperial College, Rm: 1009, x47552
Remember:
Inputs draw no current. 1K resistors to +5 V can set inputs to high or they can be set low by connecting to ground.
Outputs can draw current and can force lines to low or high.
12/11/2018
Tim Sumner, Imperial College, Rm: 1009, x47552