Upload
miguel-angelo-bernabe
View
224
Download
0
Embed Size (px)
Citation preview
8/13/2019 Chapter 4 - Ele232 [Compatibility Mode]
1/7
Chapter : DC Analysis of BJTNorsabrina Sihab
Faculty of Electrical Engineering,
Universiti Teknologi MARA
Pulau Pinang
Tel : 04-3823355
. . .
1
Chapter 4 DC Analysis of BJT2
At the end of this chapter, students able to: Analyze the dc biasing of single stage BJT amplifier circuit.
Calculates DC volta es and DC currents.
Calculates maximum output voltage, VO(max).
Electronics 1Updated May 2011NorsabrinaSihab
Chapter 4 DC Analysis of BJT3
BiasingBiasing refers to the DC voltages applied to a transistor in order toturn it on so t at it can amp i y t e AC signa .
The DC input establishes an operating or quiescent point called the
QQ--pointpoint.In DC analysis all capacitor act as open circuit.
DC Biasing circuits
1. Fixed-bias circuit
2. Emitter-stabilized bias circuit
3. Voltage divider bias circuit
Electronics 1Updated May 2011Norsabrina Sihab
.
5. Voltage feedback
Chapter 4 DC Analysis of BJT4
Proper biasing circuit which it operate in linear region and circuithave centered Q-point or midpoint biased
mproper as ng cause
Distortion in the output signal
Produce limited or clipped at output signali o
A
Linear operation for an inverting amplifier
Electronics 1Updated May 2011NorsabrinaSihab
Non-linear operation for an inverting amplifier
8/13/2019 Chapter 4 - Ele232 [Compatibility Mode]
2/7
Chapter 4 DC Analysis of BJT5
-
Electronics 1Updated May 2011Norsabrina Sihab
Chapter 4 DC Analysis of BJT6
1) Fixed-bias circuit - DC analysis
Input LoopInput Loop Output LoopOutput Loop
12
KVL at loop 1: The collector current is given by:
Solving for the base current:
CC B B BE =
KVL at loop 2 :
)2(= BIIC
Electronics 1Updated May 2011NorsabrinaSihab
)1(R
VVI
B
BECCB
=
)3(=
=
CCCCCE
CECCCC
RIVV
Chapter 4 DC Analysis of BJT7
Load Line for FixedLoad Line for Fixed--bias circuitbias circuit
)3(= RIVV
From equation (3) :
The end points of the load line
are:
VVC
CC
satC
CE
R
VI
0=
=
AICCsatCE CVV
0==
where the value of RBB sets the value of IBB
he Q-point is the particular operating point:
Electronics 1Updated May 2011Norsabrina Sihab
that sets the values of VCECE and ICC
Chapter 4 DC Analysis of BJT8
Circuit Values Affect the QCircuit Values Affect the Q--PointPoint
Increasing level of IB
Increasing level of RC
Decreasingvalue of V
Electronics 1Updated May 2011NorsabrinaSihab
8/13/2019 Chapter 4 - Ele232 [Compatibility Mode]
3/7
Chapter 4 DC Analysis of BJT9
-
Example : Q point at midway between cut-off and saturation
Csat
ICQQ-point
Electronics 1Updated May 2011Norsabrina Sihab
CE(Cut-off)CEQ
Chapter 4 DC Analysis of BJT10
Determine a) IBQ and ICQ, b) VCEQ, c) VB and VC, d) VBC
Electronics 1Updated May 2011NorsabrinaSihab
Chapter 4 DC Analysis of BJT11
2) Emitter2) Emitter--Stabilized Bias CircuitStabilized Bias Circuit
Adding a resistor (RE) to improve the stability that is DC biascurrent and voltage remain closer to where they set eventemperature c ange.
Electronics 1Updated May 2011Norsabrina Sihab
Chapter 4 DC Analysis of BJT12
2) Emitter2) Emitter--Stabilized Bias CircuitStabilized Bias Circuit DC AnalysisDC Analysis
npu oopnpu oop u pu oopu pu oop
KVL at loop 1 :
1 2
0RI-V-RI- EEBEBBCC =+V
Since I = (+1)I :
KVL at loop 2 :
0RIVRIV EECECCCC =+
0R1)I(-RI-V EBBBCC =+ BEV
Solving for IB:
E C
-(2)-)R(RIVV ECCCCCE +=
Also: EEE RIV =
Electronics 1Updated May 2011NorsabrinaSihab
)1(1)R(R
V-VI
EB
BECCB
++=
EBEBBCCB
CCCCECEC
VVRIVV
RI-VVVV
+==
=+=
8/13/2019 Chapter 4 - Ele232 [Compatibility Mode]
4/7
Chapter 4 DC Analysis of BJT13
Load Line for EmitterLoad Line for Emitter--bias circuitbias circuit
From equation (2) :
-(2)-)R(RIVV ECCCCCE +=
The end points of the load lineare:
VVEC
CCC
CE
sat RR
VI
0=+
=
AICCCE CVV
0==
Electronics 1Updated May 2011Norsabrina Sihab
Chapter 4 DC Analysis of BJT14
Determine a) IB, b) IC, c) VCE, d) VC, e) VE, f) VB, g) VBC
Electronics 1Updated May 2011NorsabrinaSihab
Chapter 4 DC Analysis of BJT15
3) Voltage Divider Bias3) Voltage Divider Bias
This is a very stable.
The currents and
independent ofvariations in .
There are two waysof analyzing thevoltage divider biascircuit :-1. Exact analysis2. Approximate
Electronics 1Updated May 2011Norsabrina Sihab
ana ys s
Chapter 4 DC Analysis of BJT16
3a) Exact Analysis
Step 1 : Redraw circuit Step 3 : Replace thevenin equiv.circuit
BEThB
VVI
=
. ep : pp y o e erm ne Band VCE
ETh ++
( )ECCCCCE RRIVV +=
Electronics 1Updated May 2011NorsabrinaSihab
21RRRTh=21
2
2 RRVV CCRTh
+==
8/13/2019 Chapter 4 - Ele232 [Compatibility Mode]
5/7
Chapter 4 DC Analysis of BJT17
Determine VCE and IC
Electronics 1Updated May 2011Norsabrina Sihab
Chapter 4 DC Analysis of BJT18
Used for circuit that have a very smallIB due to large resistance between
.
If Ri R2, IB < I2. So approx. I1 I2
E 2.
21
CC2B
RR
VRV
=
V
BEBE VVV
EE
RI =
EECCCCCE RI-RI-VV =
II CE
Electronics 1Updated May 2011NorsabrinaSihab
)R(R-IVV ECCCCCE
Chapter 4 DC Analysis of BJT19
Determine VCE and IC
Electronics 1Updated May 2011Norsabrina Sihab
Chapter 4 DC Analysis of BJT20
4) DC Bias with Voltage Feedback
Another way toimprove the stabilityof a bias circuit is toadd a feedback pathfrom collector tobase.
In this bias circuitthe Q-point is only
on the transistor
beta, .
Electronics 1Updated May 2011NorsabrinaSihab
8/13/2019 Chapter 4 - Ele232 [Compatibility Mode]
6/7
Chapter 4 DC Analysis of BJT21
KVL at input loop:
0= EEBEBBCCCC RIVRIRIV
B C, .
CBCC IIII += EC II
Knowing IC = IB and IE IC, theloop equation becomes:
= 1
VV
EBBEBBCBCC
Solving for IB:
Electronics 1Updated May 2011Norsabrina Sihab
)R(RRI
ECB
B++
=
Chapter 4 DC Analysis of BJT22
KVL at output loop:IERE + VCE + ICRC VCC = 0
Since IC IC as IB=0 and IC = IB:I (R + R ) + V V =0
Solving for VCE:
VCE = VCC IC(RC + RE)
Electronics 1Updated May 2011NorsabrinaSihab
Chapter 4 DC Analysis of BJT23
Determine IB and VC
Electronics 1Updated May 2011Norsabrina Sihab
Chapter 4 DC Analysis of BJT24
1) COLLECTOR FEEDBACK
Determine ICQ, VCEQ, VB, VC, VE and VBC
Vcc = +20V
CB
B2
Vo
Electronics 1Updated May 2011NorsabrinaSihab
8/13/2019 Chapter 4 - Ele232 [Compatibility Mode]
7/7
Chapter 4 DC Analysis of BJT25
2) Common Collector
Determine VCEQ and IE
Electronics 1Updated May 2011Norsabrina Sihab
Chapter 4 DC Analysis of BJT26
3) Common Base
Determine VCB, IB and VCE
CB Co
VoVi
E C
EE CC
Electronics 1Updated May 2011NorsabrinaSihab
Chapter 4 DC Analysis of BJT
27
Electronics 1Updated May 2011Norsabrina Sihab