19/04/23 Tim Sumner, Imperial College, Rm: 1009, x47552

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TransistorsTransistors

19/04/23 Tim Sumner, Imperial College, Rm: 1009, x47552

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Review : What is a Transistor ?Review : What is a Transistor ?

FOR MORE INFO...

Relevant Books: Art of Electronics + Lab: Harowitz and HillHarowitz and Hill

Electronic Circuits: E.C. Lowenberg, SCHAUM SERIESE.C. Lowenberg, SCHAUM SERIES

Electric Circuits: J.A. EDMINISTER SCHAUM SERIESJ.A. EDMINISTER SCHAUM SERIES

NPN Transistor Rules:VC > VE

VB = VE + 0.6 Volts I C = I B

I E = I C + I B I E = (1 + ) I B

IB : Base Current

Emitter

Collector

Base

IE : Emitter Current

IC : Collector Current

19/04/23 Tim Sumner, Imperial College, Rm: 1009, x47552

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Some Transistor Applications ISome Transistor Applications I

- V

Current Source Follower:

IE = 1 mA

IC

Vin= 5.6 V

Vout= 5.0 V

Load

R = 5 K

+ V

+ V

Vin

IE

IC

Vout= Vin+ 0.6 Volts

19/04/23 Tim Sumner, Imperial College, Rm: 1009, x47552

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Some Transistor Applications IISome Transistor Applications II

RE << IE = IC >>

RC >> Vout >>

VoutVin = VB

Vin = VE

+ V

- V

+ V

Qdown

Qup

Push-Pull : Common Emitter Amplifier :

19/04/23 Tim Sumner, Imperial College, Rm: 1009, x47552

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The Emitter Follower IThe Emitter Follower I

~

SourceLoad

Vcc

Ic

(1) R3=7.5 V/0.5 mA = 15K

Rbase= VB/IB = 1.64 M(2) R(2) RTHTH(divider) = 1/10 R(divider) = 1/10 RBB

RRB B = 164 K = 164 K

RR11 = R = R22= 328 K= 328 K

R1

R2 R3

1F

4.7 K

10 K

What about C1 ?

Given : Vcc = 15 Volts Ic = 0.5 mA; = 100 f(100 Hz) = 3 db

C1

19/04/23 Tim Sumner, Imperial College, Rm: 1009, x47552

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The Emitter Follower IIThe Emitter Follower II

~

SourceLoad

Vcc

Ic328 K

328K

15 K

1F

4.7 K

10 K

(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=(1/2RC) 0.014 F

= 100 f(100 Hz) = 3 db

C1

19/04/23 Tim Sumner, Imperial College, Rm: 1009, x47552

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Emitter Follower (a bit diff.)Emitter Follower (a bit diff.)

Rin=Rload(1+)

Rout=Rsource/(1+)

19/04/23 Tim Sumner, Imperial College, Rm: 1009, x47552

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Common Emitter AmplifierCommon Emitter Amplifier

Gain = R5/R2Gain = R5/R2

RRoutout=R=R55

19/04/23 Tim Sumner, Imperial College, Rm: 1009, x47552

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Common Emitter Amplifier IICommon Emitter Amplifier II

19/04/23 Tim Sumner, Imperial College, Rm: 1009, x47552

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The Ebers-Moll Model for BJTThe Ebers-Moll Model for BJT

19/04/23 Tim Sumner, Imperial College, Rm: 1009, x47552

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Temperature EffectsTemperature Effects

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Temperature Effects and Current Temperature Effects and Current Mirrors Mirrors

19/04/23 Tim Sumner, Imperial College, Rm: 1009, x47552

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ExercisesExercises

Make a Current Source using a transistor

Make common emitter followerMake a Common Emitter Amplifier

19/04/23 Tim Sumner, Imperial College, Rm: 1009, x47552

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A .OR. B

Making Gates using Transistors IMaking Gates using Transistors I

+5 Volts

InPut A

InPut B

19/04/23 Tim Sumner, Imperial College, Rm: 1009, x47552

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A .OR. B

Making Gates using Transistors IIMaking Gates using Transistors II

InPut A

InPut B

A A OUT

1 0 0

1 1 0

0 1 0

0 0 1

Here is what we

have made

19/04/23 Tim Sumner, Imperial College, Rm: 1009, x47552

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A .AND. B

Exercise IExercise I

InPut A

InPut BA A OUT

1 0 0

1 1 1

0 1 0

0 0 0

Design and construct an AND gate using transistors and resistors :

The AND gate TRUTH table

19/04/23 Tim Sumner, Imperial College, Rm: 1009, x47552

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A .AND. B

Exercise I continuedExercise I continued

InPut A

InPut B

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.

‘0’

‘1’

‘0’

5 V

5 V

19/04/23 Tim Sumner, Imperial College, Rm: 1009, x47552

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Answer (almost):Answer (almost):

Not quite because this is a NAND gate but we do knowNot quite because this is a NAND gate but we do knowby now how to invert using a transistorby now how to invert using a transistor

TTLTTL CMOSCMOS

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Important conclusionImportant 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

19/04/23 Tim Sumner, Imperial College, Rm: 1009, x47552

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Remember: 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.