electronics lecture6 7 bjt - aziz mohaisen · department of electrical, electronics and...
TRANSCRIPT
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
Department of EECE
Bipolar Junction Transistors
Electronic Circuits
Manar Mohaisen Office: F208
Email: [email protected]
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Explain the Operation of the Zener Diode
₪ Explain Applications of the Zener Diode
₪ Explain the Operation and Applications of the Varactor Diode
₪ Explain the Operation and Applications of the Optical Diodes
₪ Other Types of Diodes
Review of Precedent Class
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Bipolar Junction Transistor (BJT)
₪ BJT Characteristics and Parameters
₪ BJT as an Amplifier and as a Switch
₪ Phototransistor and its Applications
₪ Transistor Categories and Packaging
₪ Discussions
Class Objectives
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ BJT ■ Consists of three regions called emitter, base, and collector.
►The base region is thin and lightly doped.
►The emitter region is heavily doped wide region.
►The controller region is moderately doped wide region.
■ Consists of two pn junctions ►Namely, base-emitter junction and base-controller junctions.
Bipolar Junction Transistor
B(base)
C (collector)
n
p
n
Base-Collectorjunction
Base-Emitterjunction
E (emitter)
B
C
p
n
E
p
npn pnp
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ BJT Operation ■ Base Current
►Electrons flow from the emitter to the base generating hole current.
● Electrons from the emitter recombine with the holes in the base.
►Since the base region is thin
● The number of holes is small.
● The number of electrons combining with the holes is also small.
● These valence electrons become free in the metallic base. This is called the base current.
Bipolar Junction Transistor – contd.
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ BJT Operation – contd. ■ Collector Current
►Base region is thin.
● most of the electrons entering the base don’t combine with holes.
● The uncombined free electrons are attracted by the collector supply voltage.
● The uncombined free electrons move through the collector into the external circuit.
Bipolar Junction Transistor – contd.
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Transistor Currents
Bipolar Junction Transistor – contd.
E B CI I I= +
IE IE
IC
IB
IC
IBn
p
n
p
n
p
+
– +
–
–+
IE
IC
IB
+
–
+
IE
IC
IB
+
–
–
(1) BJT currents (2) DC Beta
CDC
B
IIβ =
(3) DC Alpha
CDC
E
IIα =
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Transistor DC Model [Unsaturated BJT] ■ Input circuit: forward-biased diode with a current of IB.
■ Output circuit: a dependent current source of βDC IB.
BJT Characteristics and Parameters
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ BJT Circuit Analysis ■ VBE = 0.7 V
►Forward-biased diode.
►Therefore,
■ IB is given by:
■ IC is given by:
■ VCE is given by:
■ VCB is given by:
BJT Characteristics and Parameters – contd.
BR BB BEV V V= −
BB BEB
B
V VI R−
=
BC DCI Iβ=
CE CC C CV V I R= −
BECB CEV V V= −
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Example 4-2 ■ βDC = 150
►Currents:
►Voltages:
BJT Characteristics and Parameters – contd.
BB BEB
B
5V 0.7V 430 A10kV VI R μ− −= = =
Ω
BC DC 150 430 A 64.5 mAI Iβ μ= = × =
64.9mAE B CI I I == +
CE CC C C 10V (64.5mA)(100 ) 3.55VV V I R= − = − Ω =
BECB CE 3.55V 0.7V 2.85VV V V= − = − =
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Collector Characteristic Curves ■ Saturation region
►Both junctions are forward- biased
● VCC = 0.
► IC is independent of IB.
►As VCC increases, IC and VCE increase.
► Ideally, when VCE exceeds 0.7, the base-collector junction becomes reverse-biased.
● The BJT goes into the linear region (active region).
● In linear region, IC is dependent on IB.
BJT Characteristics and Parameters – contd.
IC
BC
A0 0.7 V VCE(max)
VCE
Saturation region
Active region
Breakdown region
BC DCI Iβ=
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Collector Characteristic Curves – contd. ■ At higher voltages of VCE
►The base-collector junction goes in breakdown.
►The collector current increases rapidly.
►A transistor should never be operated in the breakdown region.
BJT Characteristics and Parameters – contd. IC
BC
A0 0.7 V VCE(max)
VCE
Breakdown region
Saturation region
Active region
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Cutoff ■ This region of operation happens when IB = 0.
►There will be a very small collector leakage current ICEO.
►This ICEO is neglected and therefore VCE = VCC.
►Both junctions are reverse-biased.
BJT Characteristics and Parameters – contd.
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Saturation ■ As VBB increases, the base-emitter junction is forward-biased.
►The base current IB increases.
■ The base current increases and the collector current increases as a result (IC = βDCIB). ►As a result, VCE decreases till the saturation value VCE (sat) and the base
-controller junction becomes forward-biased (VCE = VCC – ICRC).
► IC does not increase anymore even when IB increases.
■ Saturation occurs below the knee of the collector curves ►A few tenths of a volt.
BJT Characteristics and Parameters – contd.
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ DC Load Line ■ In between cutoff and saturation along the load line is the active
region. ►Details will be covered in Chapter 5.
BJT Characteristics and Parameters – contd.
0
IC
VCE
IB = 0 Cutoff
VCE(sat) VCC
IC(sat)
Saturation
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Example 4-4 ■ Determine whether or not the transistor is in saturation or not.
►VCE(sat) = 0.2 V.
■ Solution ► If the transistor is in saturation, then
► If the transistor is not in saturation, then
● and
►Because IC can’t be greater than IC(sat), the transistor is saturated.
BJT Characteristics and Parameters – contd.
CC C(sat)C(sat)
B
10V 0.2V 9.8mA1.0 kV V
I R− −= = =
Ω
BB BEB
B
2.3 V 0.23 mA10kV VI R
−= = =Ω
BC DC (50)(0.23mA) 11.5 mAI Iβ= = =
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ More About βDC
■ βDC is not really constant but rather varies with IC and the temperature. ►Usually we specify the minimum βDC in the transistor datasheet.
BJT Characteristics and Parameters – contd.
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Maximum Transistor Rating ■ Limitations (maximum ratings) are specified by the manufacturer
for: ►Collector-to-base voltage
►Collector-to-emitter voltage
►Collector current
►Power dissipation
■ Note that ►Collector-to-emitter voltage and collector current can’t be maximum
at the same time.
► If VCE is maximum, IC is given by:
► If IC is maximum, VCE is given by:
BJT Characteristics and Parameters – contd.
D(max)C
CE
PI V=
D(max)CE
C
PV I=
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Example 4-5 ■ Collector-to-emitter voltage = 6 V.
■ Maximum power rating = 250 mW.
■ Find the maximum collector current.
■ Solution:
BJT Characteristics and Parameters – contd.
D(max)C
CE
250 mW 41.7 mA6 VP
I V= = =
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Example 4-6 ■ PD(max) = 800 mW,
■ VCE(max) = 15 V,
■ and IC(max) = 100 mA.
■ Determine the maximum value of
VCC before exceeding the rating.
■ Solution:
● IC is much less than the maximum collector maximum current.
● IC is dependent on IB, and will not change as long as IB is fixed.
● Therefore,
● Has the maximum power rating been exceeded? No.
BJT Characteristics and Parameters – contd.
BB BEB
B195 AV VI R μ−= = BC DC (100)(195 A) 19.5mAI Iβ μ= = =
C C C (19.5mA)(1.0k ) 19.5 VRV I R= = Ω =
CCC(max) CE(max) 15V 19.4 V 34.5 VRV V V= + = + =
D CCE(max) (15V)(19.5mA) 293 mWP V I= = =
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Derating PD(max)
■ PD(max) is usually specified at 25oC.
■ For higher temperatures, PD(max) is less.
■ Derating is calculated using a derating factor.
■ Example
►A derating factor of 2 mW/oC
● This means that the maximum power dissipation is reduced 2 mW for each degree Celsius increase in temperature.
BJT Characteristics and Parameters – contd.
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Voltage Gain ■ Defined as the ratio between output voltage and input voltage.
■ Let us define re’ as the resistance between base and emitter.
■ Then,
►Voltage gain
■ Example: ► re
’ = 50 Ω
►RC = 1.0 k Ω
The BJT as an Amplifier
'e ebV I r= c e CV I R≅
C C' '
ecve e eb
I R RVA V I r r== ≅
C'
1000 2050ve
RAr
= =≅
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Switch ■ Condition in Cutoff
■ Conditions in Saturation
The BJT as a Switch
RB
0 V
RC IC = 0
+VCC
RC
C
E
+VCC
IB = 0 –
+RB
RC IC(sat)
+VCC
RC
C
E
+VCC
IB
+VBB
IC(sat)
Cutoff – open switch Saturation – closed switch
CCCE(cutoff)V V=
CC CE(sat)C(sat)
C
V VI R
−= C(sat)
B(min)DC
II β=
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Application of a Transistor Switch ■ In cutoff diode is off.
■ In saturation diode is on.
₪ Example ■ The diode requires 30 mA to be on.
■ Use double the minimum base current to ensure saturation. ►VCC = 9V, VCE(sat) = 0.3 V, RC = 220 Ω, RB = 3.3 kΩ.
►Determine the value of the square wave.
The BJT as a Switch – contd.
LEDCC CE(sat)C(sat)
C
9V 1.6V 0.3V 32.3mA220V V V
I R− − − −= = =Ω
C(sat)B(min)
DC
32.3mA 646 A50I
I μβ= = =
B BEB(min)2 (1.29mA)(3.3k ) 0.7 V 4.96VinV I R V= + = Ω + =
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Phototransistor ■ The base current is produced when light strikes the sensing
semiconductor base region. ► In absence of light, there will be a small leaking current ICEO.
■ When the light strikes the collector-base pn junction ►A base current, Iλ, is produced that is directly prop. with the light
intensity.
■ Except for the base current generation, ►The phototransistor behaves
as a conventional BJT.
►The base-collector region
is wider than that in the case
of the BJT.
● To produce greater current.
The Phototransistor
Collector
Emitter
Light
n p
n
Base
RC
+V
VO U T
CC
C DCI Iλβ=
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Three-lead phototransistor ■ The base lead is electrically available where the phototransistor
can be used as a BJT with or without light-sensitivity.
₪ Two-lead phototransistor ■ The base lead is not electrically available.
►This is the usual configuration.
The Phototransistor – contd.
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Collector Characteristics Curves ■ Each curve corresponds to a certain value of light intensity.
■ Phototransistors are not sensitive to all lights ►They are sensitive to wavelengths in the red and infrared bandwidths.
The Phototransistor – contd.
RC
+V
VO U T
CC
Dark current
50 10 15 20 25 30VCE (V)
10
8
6
4
2
IC (mA)
50 mW/cm2
40 mW/cm2
30 mW/cm2
20 mW/cm2
10 mW/cm2
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Applications ■ Light activating.
■ Light deactivating.
The Phototransistor – contd.
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Optocouplers ■ A device that has light-based connection.
₪ Types of Optocouplers ■ LED-to-photodiode
■ LED-to-phototransistor
₪ Current transfer ration ■ Ration between change in input current (LED’s) and that of the
out current.
The Phototransistor – contd.
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Applications of the Optocouplers ■ Isolate sections of the circuit that are incompatible in terms of
current or voltage. ►Ex.: Isolate low-current control or circuits from noisy power supplies
or high current motors, etc.
►Ex.: Isolating patients from monitoring instruments.
►Ex.: Traffic lights where control circuit is isolated from the power circuit.
The Phototransistor – contd.
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ General-purpose / Small-signal Transistors ■ Used for low- or medium-power amplifiers or switches.
■ The packages are either metal or plastic.
■ Certain types of packages contain multiple transistors.
Transistor Categories and Packaging
12 3
1 Emitter
2Base
3 Collector
TO-92
2 Emitter
1Base
3 Collector
12
3
SOT-23
1 Emitter
2Base
3 Collector
3 21
TO-18
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ Power Transistors ■ Used to handle large currents ( > 1 A) and/or large voltages.
►A power amplifier is used to drive the speakers.
■ Usually it has a metal case for the collector ►Usually connected to a heat sink for heat dissipation.
Transistor Categories and Packaging – contd.
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
₪ RF Transistors ■ Operate at extremely high-frequencies.
■ Usually used in communication systems.
Transistor Categories and Packaging – contd.
Korea University of Technology & Education
Department of Electrical, Electronics and Communications Engineering
Discussion & Notes
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