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QUEENSBOROUGH COMMUNITY COLLEGE
Department of Engineering Technology
ET210 Lab 8: Bipolar Junction Transistor Emitter Stabilized Bias, Voltage-Divider
Bias, and (Collector) Voltage Feedback Bias Circuits
Objectives:
1) To construct an Emitter Stabilized Bipolar Junction Transistor (BJT) Bias Circuit.
2) To measure the Quiescent Voltages and Currents in an Emitter Stabilized BJT
Bias Circuit.
3) To plot the DC Load Line of an Emitter Stabilized BJT Bias Circuit.
4) To calculate the theoretical Quiescent Voltages and Currents established in
an Emitter Stabilized BJT Bias Circuit.
5) To construct a Voltage-Divider Bias Circuit.
6) To measure the Quiescent Voltages and Currents in a Voltage-Divider Bias
Circuit.
7) To plot the DC Load Line of a Voltage-Divider Bias Circuit.
8) To calculate the theoretical Quiescent Voltages and Currents established in
a Voltage-Divider Bias Circuit.
9) To compare the measured and calculated values of the Quiescent Voltages and
Currents.
10) To apply an ac input signal through a coupling capacitor to the Voltage-Divider
Bias Circuit in a Common-Emitter configuration and observe the output voltage.
11) To calculate the voltage gain of the Common-Emitter Amplifier (with input
coupling capacitor and
no
emitter bypass capacitor)
12) To construct a (Collector) Voltage Feedback Bias Circuit, measure the Quiescent
Voltages and Currents, and calculate their theoretical values.
Equipment Required:
DC Power Supply
Digital Multimeter (DMM)
Function Generator
Oscilloscope
Components Required:
Bipolar Junction Transistor (NPN):
2N4401
Resistors (1/4 Watt or above):
1
k
Ω, 430
k
Ω, 470 Ω, 1.1
k
Ω, 10
k
Ω, 2.2
k
Ω, 390 Ω, 1.3
k
Ω,
240
k
Ω, 200 Ω
Capacitor (rated 25 V or above): 10 µF
Laboratory Experiment Procedure:
1)
Measure
the resistance value of each resistor and record the measurements below:
Resistor with nominal color code value of 1
k
Ω
Measured
resistance value
=
_________928kohms_____________
QCC
ECET
John Buoncora
Page 1
BJT Emitter Stabilized Bias, Voltage-Divider Bias, and (Collector) Voltage Feedback Bias Circuits
Resistor with nominal color code value of 430
k
Ω
Measured
resistance value
=
________428kohms______________
Resistor with nominal color code value of 470 Ω
Measured
resistance value
=
________496ohms______________
Resistor with nominal color code value of 1.1
k
Ω
Measured
resistance value
=
__________1.13k____________
Resistor with nominal color code value of 10
k
Ω
Measured
resistance value
=
__________9.96k____________
Resistor with nominal color code value of 2.2
k
Ω
Measured
resistance value
=
_________2.2k_____________
Resistor with nominal color code value of 390 Ω
Measured
resistance value
=
________394.41______________
Resistor with nominal color code value of 1.3
k
Ω
Measured
resistance value
=
_______1.19k_______________
Resistor with nominal color code value of 240
k
Ω
Measured
resistance value
=
___________236.52___________
Resistor with nominal color code value of 200 Ω
Measured
resistance value
=
_________237.72_____________
2) Refer to the diagram below for the 2N4401 transistor pin-out or refer to the data sheet for
the 2N4401 transistor in a TO-92 package (E = Emitter, B = Base, C = Collector).
QCC
ECET
John Buoncora
Page 2
BJT Emitter Stabilized Bias, Voltage-Divider Bias, and (Collector) Voltage Feedback Bias Circuits
Bipolar Junction Transistor Emitter Stabilized Bias Circuit
:
3) Construct the Emitter Stabilized Bias Circuit, shown in Figure-1 with DC Supply Voltage
V
CC
= + 15 V
.
Figure-1: Emitter Stabilized Bias Circuit
4) Set the power supply output to ON and adjust/set the
Vcc
supply voltage to
+ 15 Volts
.
Emitter Stabilized Bias Circuit Measurements
5) Record the
measured
values of the following DC voltages for the circuit in Figure-1:
V
CC
(DC Supply Voltage)
=
________15.09V_____________
V
B
(Base to Ground Voltage)
=
__________9.3V___________
V
C
(Collector to Ground Voltage)
=
___________9.95V__________
V
E
(Emitter to Ground Voltage)
=
____________2.4V_________
V
CEQ
(Collector to Emitter Voltage) =
_________7.55V____________
V
RC
(Voltage across resistor R
c
)
=
____________5.1V_________
QCC
ECET
John Buoncora
Page 3
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BJT Emitter Stabilized Bias, Voltage-Divider Bias, and (Collector) Voltage Feedback Bias Circuits
V
RB
(Voltage across resistor R
B
)
=
___________9.3V__________
6) Calculate the following DC quantities using the
measured voltage
values from step 5 and the
measured
resistance
values from step 1:
Quiescent DC Collector Current I
CQ
=
V
RC
/ R
C
(use V
RC
and
not
V
C
in the numerator)
I
CQ
=
_______5.1mA____________
Quiescent DC Emitter Current I
EQ
=
V
E
/ R
E
I
EQ
=
________5.1mA____________
Quiescent DC Base Current I
BQ
= V
RB
/ R
B
(use V
RB
and
not
V
B
in the numerator)
I
BQ
=
________21.62uA____________
Transistor Beta β =
I
CQ
/ I
BQ
β =
_________235.89_____________
Calculated Quiescent Collector to Emitter Voltage V
CEQ
=
V
C
–
V
E
V
CEQ
= ________7.55V_____________
Calculated R
c
resistor Voltage V
RC
=
V
CC
–
V
C
(DC Supply Voltage minus Collector to Ground
Voltage)
V
RC
=
________5.09V______________
Calculated R
B
resistor Voltage V
RB
=
V
CC
–
V
B
(DC Supply Voltage minus Base to Ground
Voltage)
V
RB
=
________5.74V______________
Compare the
calculated
values of V
CEQ
, V
RC
, and V
RB
from step 6 to the corresponding
measured
values of V
CEQ
, V
RC
, and V
RB
from step 5.
Comparison results: _____the calculated
___________________________________________________
_________________________________________________________________________
_________________________________________________________________________
Do the results of your comparison provide a verification of Kirchhoff's Voltage Law (KVL)?
______yes______________
QCC
ECET
John Buoncora
Page 4
BJT Emitter Stabilized Bias, Voltage-Divider Bias, and (Collector) Voltage Feedback Bias Circuits
Calculated Quiescent Base to Emitter Voltage V
BEQ
=
V
B
–
V
E
V
BEQ
= _________1.75V____________
Compare the value obtained above for V
BEQ
with the typical approximate value of 0.7 V for
the DC Base-Emitter Voltage of a Silicon transistor.
__________________________________________________________________________
Compare the "measured" values of I
CQ
, I
EQ
, and I
BQ
from step 6 to each other.
Comparison results: ________________________________________________________
_________________________________________________________________________
_________________________________________________________________________
Do the results of your comparison agree with the transistor active region equation I
C
= β × I
B
?
_________5.09mA____________
Do the results of you comparison agree with Kirchhoff's Current Law (KCL) as applied to the
transistor I
E
= I
C
+
I
B
?
_________yes_______________
(Note: Since I
C
is much greater than I
B
, it may be difficult to
verify that KCL is satisfied using the "measured values", which
are not precise enough for this question. In such a case, you
may simply state that the "measured" currents are
not precise
enough for this question.)
7) Find the
Collector Saturation current I
C(SAT)
using the
approximate
equation provided below
for the Emitter-Stabilized Bias Circuit of Figure-1:
I
C (SAT)
= (V
CC
–
V
CE (SAT)
) / (R
C
+
[R
E
/ α])
I
C (SAT)
≈ V
CC
/ (R
C
+
R
E
)
(
approximate
, since the
ideal
V
CE (SAT)
= 0 V,
the practical V
CE (SAT)
<= 0.3 V typically, and α is slightly
less than one)
I
C (SAT)
= ________10.23mA_____________________
8) Find the Collector to Emitter Cutoff Voltage using the equation provided below for
the Emitter-Stabilized Bias Circuit of Figure-1:
V
CE (cutoff)
= V
CC
QCC
ECET
John Buoncora
Page 5
BJT Emitter Stabilized Bias, Voltage-Divider Bias, and (Collector) Voltage Feedback Bias Circuits
V
CE (cutoff)
= __________15.04V__________________
9) Sketch the DC Load Line for the Emitter-Stabilized Bias circuit of Figure-1 and label the current
and voltage values for saturation, cutoff, and the Quiescent operating point (Q point).
10) Set the power supply output to OFF and disassemble the circuit of Figure-1.
Bipolar Junction Transistor Voltage-Divider Bias Circuit
:
Voltage-Divider Bias Circuit Measurements
11) Construct the Voltage-Divider Bias Circuit, shown in Figure-2 with DC Supply Voltage
V
CC
= + 15 V
.
2N4401
RC
1.1kΩ
R1
10kΩ
Vcc = + 15 V
Vc
VB
RE
390 Ω
VE
+
_
VCE
R2
2.2kΩ
+
_
VBE
Figure-2: Voltage-Divider Bias Circuit
QCC
ECET
John Buoncora
Page 6
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BJT Emitter Stabilized Bias, Voltage-Divider Bias, and (Collector) Voltage Feedback Bias Circuits
12) Set the power supply output to ON and adjust/set the
Vcc
supply voltage to
+ 15 Volts
.
13) Record the
measured
values of the following DC voltages for the circuit in Figure-2:
V
CC
(DC Supply Voltage)
=
____15.06V_________________
V
B
(Base to Ground Voltage)
=
_______3.26V______________
V
C
(Collector to Ground Voltage)
=
_________3.96V____________
V
E
(Emitter to Ground Voltage)
=
_______3.87V______________
V
CEQ
(Collector to Emitter Voltage) =
_______89.43mV______________
V
RC
(Voltage across resistor R
c
)
=
_________11.104V____________
V
R1
(Voltage across resistor R
1
)
=
_________11.80V____________
14) Calculate the following DC quantities using the
measured voltage
values from step 13 and
the
measured
resistance
values from step 1:
Quiescent DC Collector Current I
CQ
=
V
RC
/ R
C
(use V
RC
and
not
V
C
in the numerator)
I
CQ
=
______10.09mA_____________
Quiescent DC Emitter Current I
EQ
=
V
E
/ R
E
I
EQ
=
______9.92mA______________
R
1
resistor DC Current I
R1
= V
R1
/ R
1
I
R1
=
_________1.18mA___________
R
2
resistor DC Current I
R2
= V
R2
/ R
2
=
V
B
/ R
2
I
R2
=
_______1.48mA_____________
DC Base Current I
BQ
=
I
R1
–
I
R2
I
BQ
= ________-300uA_____________ (
Note: This calculation involves the difference between two
currents that have
almost
the same value. Therefore, the
calculated value
of the Base Current may
not
be accurate.
Use as many significant digits as possible in the calculation.)
QCC
ECET
John Buoncora
Page 7
BJT Emitter Stabilized Bias, Voltage-Divider Bias, and (Collector) Voltage Feedback Bias Circuits
Step 14 Continued:
Calculated Quiescent Collector to Emitter Voltage V
CEQ
=
V
C
–
V
E
V
CEQ
= ________0.09V_____________
Calculated R
c
resistor Voltage V
RC
=
V
CC
–
V
C
(DC Supply Voltage minus Collector to Ground
Voltage)
V
RC
=
________11.8V______________
Calculated R
1
resistor Voltage V
R1
=
V
CC
–
V
B
(DC Supply Voltage minus Base to Ground
Voltage)
V
R1
=
_____11.19V_________________
Compare the
calculated
values of V
CEQ
, V
RC
, and V
R1
from step 14 to the corresponding
measured
values of V
CEQ
, V
RC
, and V
R1
from step 13. State the fundamental circuit law that
was used to obtain the equations provided above for V
CEQ
, V
RC
, and V
R1
in step 14.
Comparison results: ________________________________________________________
_________________________________________________________________________
_________________________________________________________________________
Fundamental Circuit Law used for V
CEQ
, V
RC
, and V
R1
in step 14: _________________________
_________________________
15) Find the
Collector Saturation current I
C(SAT)
using the
approximate
equation provided below
for the Voltage-Divider Bias Circuit of Figure-2:
I
C (SAT)
≈ V
CC
/ (R
C
+
R
E
)
I
C (SAT)
= _____________________________
16) Find the Collector to Emitter Cutoff Voltage using the equation provided below for
the Voltage-Divider Bias Circuit of Figure-2:
V
CE (cutoff)
= V
CC
V
CE (cutoff)
= ____________________________
QCC
ECET
John Buoncora
Page 8
BJT Emitter Stabilized Bias, Voltage-Divider Bias, and (Collector) Voltage Feedback Bias Circuits
17) Sketch the DC Load Line for the Voltage-Divider Bias Circuit of Figure-2 and label the current
and voltage values for saturation, cutoff, and the Quiescent operating point (Q point).
Common-Emitter Amplifier with Voltage-Divider Bias:
18) Set the power supply output to OFF.
Refer to Figure-3
and
add
the
10 µF coupling capacitor
(observe capacitor polarity) to the circuit that you previously constructed for Figure-2 in
order to
obtain the circuit of Figure-3
(see the next page for Figure-3).
QCC
ECET
John Buoncora
Page 9
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BJT Emitter Stabilized Bias, Voltage-Divider Bias, and (Collector) Voltage Feedback Bias Circuits
DC Supply Voltage V
CC
= + 15 V
Figure-3: Common-Emitter Amplifier with Voltage-Divider Bias
Note: Observe polarity on the electrolytic capacitor C1 as shown above when
wiring the circuit (Danger: Electrolytic Capacitors can explode and cause eye
injury if they are connected incorrectly or if the voltage ratings of the capacitors
are exceeded). Ask your instructor to verify the capacitor connections before
applying power to the circuit.
19)
Set the power supply output to ON and adjust/set the
Vcc
supply voltage to
+ 15 Volts
.
20) Apply a
1.5 V peak-to-peak
, 1kHz sinusoidal voltage to the input [Vin relative to
ground] of the circuit in
Figure-3
. Set the function generator output as necessary
to obtain
an input voltage Vin =
1.5 V
peak-to-peak
(sine wave at a frequency of 1 kHz) as indicated
on the oscilloscope
.
21) Monitor the
Base to Ground Voltage V
B (AC + DC)
on channel 1 of the oscilloscope and monitor
QCC
ECET
John Buoncora
Page 10
BJT Emitter Stabilized Bias, Voltage-Divider Bias, and (Collector) Voltage Feedback Bias Circuits
the
Collector to
Ground Voltage V
C (AC + DC)
on channel 2 of the oscilloscope as shown in
Figure-3
.
Set the oscilloscope channel 1
and
channel 2
coupling
to
DC
.
Step 21 Continued:
Sketch the input and output voltage waveforms and show the correct phase relationship
between them.
Label all of the peak voltage values and peak-to-peak voltage values, along with the DC
component (average) voltage level of the V
B (AC + DC)
and V
C (AC + DC)
voltage waveforms. Find the
measured voltage gain A
V
of the amplifier based on the
peak-to-peak
value of V
B (AC + DC)
and the
measured
peak-to-peak
value of V
C (AC + DC)
.
Record the data and measured voltage gain A
V
under Step 21 Data.
Step 21 Data: V
B (AC + DC)
and V
C (AC + DC)
Voltage Waveforms
Peak-to-Peak
value of V
B (AC + DC)
=
_______1.76V_________________
(Base to Ground Voltage)
Peak-to-Peak
value of V
C (AC + DC)
=
______7.26V__________________ (
Collector to
Ground
Voltage)
Be sure to use
Peak-to-Peak
voltage values in the equation provided below:
Measured voltage gain A
V
=
V
C (AC + DC) Peak-to-Peak
/ V
B (AC + DC) Peak-to-Peak
QCC
ECET
John Buoncora
Page 11
BJT Emitter Stabilized Bias, Voltage-Divider Bias, and (Collector) Voltage Feedback Bias Circuits
A
V
= ___________4.125V__________ (Note: A
V
is negative if the voltages are 180° out of
phase and
positive if the voltages are in phase)
22) Set the power supply output to OFF and disassemble the circuit of Figure-3.
23) Construct the (Collector) Voltage Feedback Bias Circuit, shown in Figure-4 with DC Supply
Voltage
V
CC
= + 15 V
.
2N4401
RC
1.3kΩ
Vcc = + 15 V
RE
200 Ω
+
_
VCE
RB
240kΩ
Figure-4: (Collector) Voltage Feedback Bias Circuit
24) Set the power supply output to ON and adjust/set the
Vcc
supply voltage to
+ 15 Volts
25) Record the
measured
values of the following DC voltages for the circuit in Figure-4:
V
CC
(DC Supply Voltage)
=
____15V_________________
V
B
(Base to Ground Voltage)
=
_____14.7V________________
V
C
(Collector to Ground Voltage)
=
_______14.9V______________
V
E
(Emitter to Ground Voltage)
=
________14.1V_____________
V
CEQ
(Collector to Emitter Voltage) =
________801.096V_____________
26) Calculate the following DC quantities using the
measured voltage
values from step 25 and
the
measured
resistance
values from step 1:
QCC
ECET
John Buoncora
Page 12
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BJT Emitter Stabilized Bias, Voltage-Divider Bias, and (Collector) Voltage Feedback Bias Circuits
Quiescent DC Emitter Current I
EQ
=
V
E
/ R
E
I
EQ
=
_______70.5uA_____________
Step 26 Continued:
Calculated Quiescent Collector to Emitter Voltage V
CEQ
=
V
C
–
V
E
V
CEQ
= ________0.8V_____________
Compare the
calculated
value of V
CEQ
from step 26 to the corresponding
measured
value of V
CEQ
from step 25.
Comparison results: ________________________________________________________
_________________________________________________________________________
Calculations and Questions:
In all of the following calculations, use the measured value of β (Beta) for your 2N4401 Bipolar
Junction Transistor (BJT), which was obtained in
Step 6
of the Laboratory Experiment
Procedure. Refer to Appendix 1: Biasing Circuit Equations for various Circuits and Common-
Emitter Voltage Gain (
non
-bypassed case), which contains the appropriate equations to be
used for each of the biasing configurations.
1) Find the % Difference between the measured value of β (Beta) in step 6 of this Lab
Experiment Procedure and the value obtained for β in a previous lab experiment called:
Bipolar Junction Transistor Fixed-Bias (Base-Bias) and Digital Logic Circuits
.
Be sure that the
same particular transistor was used for each of these experiments (in the Beta measurement
and Biasing steps).
2) Calculate the theoretical Quiescent DC values of the following quantities for the Emitter
Stabilized Bias Circuit of
Figure-1 [use the measured value of
β (Beta)
]
:
Base Current
I
B
= _____________________
Quiescent Collector Current
I
CQ
=
___________________
Quiescent Emitter Current
I
EQ
=
___________________
Quiescent Collector to Emitter Voltage
V
CEQ
= _____________________
QCC
ECET
John Buoncora
Page 13
BJT Emitter Stabilized Bias, Voltage-Divider Bias, and (Collector) Voltage Feedback Bias Circuits
V
C
(Collector to Ground Voltage)
=
_____________________
V
E
(Emitter to Ground Voltage)
=
_____________________
V
B
(Base to Ground Voltage)
=
_____________________
3) Calculate the % Difference between the calculated values of I
CQ
and V
CEQ
in calculation
section 2 and the corresponding measured values of I
CQ
and V
CEQ
.
4) Calculate the theoretical Quiescent DC values of the following quantities for the Voltage-
Divider Bias Circuit of
Figure-2 [use the measured value of
β (Beta)
]
:
Thevenin Voltage
V
TH
= ______________________
Thevenin Resistance
R
TH
= ______________________
Base Current
I
B
= _____________________
Quiescent Collector Current
I
CQ
=
___________________
Quiescent Emitter Current
I
EQ
=
___________________
Quiescent Collector to Emitter Voltage
V
CEQ
= _____________________
V
C
(Collector to Ground Voltage)
=
_____________________
V
E
(Emitter to Ground Voltage)
=
_____________________
V
B
(Base to Ground Voltage)
=
_____________________
5) Calculate the % Difference between the calculated values of I
CQ
and V
CEQ
in calculation
section 4 and the corresponding measured values of I
CQ
and V
CEQ
.
6) Calculate the theoretical Voltage Gain A
V
of the Common-Emitter Amplifier with Voltage-
Divider Bias (and
no emitter bypass capacitor
of) of
Figure-3
:
A
V
= ____________________________________
7) Use Superposition to write the theoretical expressions for the voltages:
V
B (AC + DC)
and V
C (AC + DC)
that correspond to lab experiment procedure step 21.
8) Calculate the theoretical Quiescent DC values of the following quantities for the (Collector)
Voltage Feedback Bias Circuit of
Figure-4 [use the measured value of
β (Beta)
]
:
QCC
ECET
John Buoncora
Page 14
BJT Emitter Stabilized Bias, Voltage-Divider Bias, and (Collector) Voltage Feedback Bias Circuits
Base Current
I
B
= _____________________
Quiescent Collector Current
I
CQ
=
___________________
Quiescent Emitter Current
I
EQ
=
___________________
Quiescent Collector to Emitter Voltage
V
CEQ
= _____________________
V
C
(Collector to Ground Voltage)
=
_____________________
V
E
(Emitter to Ground Voltage)
=
_____________________
V
B
(Base to Ground Voltage)
=
_____________________
9) Calculate the % Difference between the calculated values of I
EQ
and V
CEQ
in calculation
section 8 and the corresponding measured values of I
EQ
and V
CEQ
.
10) Record the minimum and maximum values of
β
(also indicated as
h
FE
) indicated on the
data
sheet
for the 2N4401 transistor.
β
min
= ________________________
β
max
= ________________________
Use the minimum and maximum values of β (Beta) to calculate the Quiescent currents and
voltages for the Bias circuits of Figure-1, Figure-2, and Figure-4.
Which of these three Bias Circuits is the most stable with respect to the Quiescent operating
point values of I
CQ
and V
CEQ
(that is, which circuit has the least variation in I
CQ
and V
CEQ
when Beta
changes between the minimum and maximum Beta values)?
QCC
ECET
John Buoncora
Page 15
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BJT Emitter Stabilized Bias, Voltage-Divider Bias, and (Collector) Voltage Feedback Bias Circuits
Appendix 1: Biasing Circuit Equations for various Circuits and Common-Emitter Voltage Gain
(
non
-bypassed case).
Use V
BE
= 0.7 V and the measured value of the transistor Beta (or use Beta =
β = 185 if the
measured value is not available) for the Bipolar Junction Transistor (BJT) in the equations
provided. Note that Q means the Quiescent value of a quantity.
The following equations apply to
Figure-1: Emitter Stabilized Bias Circuit
, which is part of the
Laboratory Experiment Procedure:
I
BQ
=
(
V
CC
–
V
BE
)
/
(
R
B
+
(β + 1)R
E
)
where I
BQ
is the Base Current of the BJT
I
CQ
= β
×
I
BQ
Quiescent Collector Current I
CQ
equals the
Base Current multiplied by Beta
I
EQ
= I
CQ
+
I
BQ
where I
EQ
is the Quiescent Emitter Current
V
CEQ
=
V
CC
–
I
CQ
×
R
C
–
I
EQ
×
R
E
where V
CEQ
is the Quiescent Collector to Emitter
Voltage
V
C
=
V
CC
–
I
CQ
×
R
C
where V
C
is the DC Collector to Ground Voltage
V
E
=
I
EQ
×
R
E
where V
E
is the DC Emitter to Ground Voltage
V
B
= V
E
+
V
BE
where V
B
is the DC Base to Ground Voltage
The following equations apply to
Figure-2: Voltage-Divider Bias Circuit
, which is part of the
Laboratory Experiment Procedure:
V
THEV
= V
CC
×
(
R
2
/ (R
1
+ R
2
)
)
where V
THEV
is the Thevenin Voltage
R
THEV
= R
1
|| R
2
where R
THEV
is the Thevenin Resistance
R
1
|| R
2
represents the resistance obtained using the
equation for the combination of
parallel
resistances
QCC
ECET
John Buoncora
Page 16
BJT Emitter Stabilized Bias, Voltage-Divider Bias, and (Collector) Voltage Feedback Bias Circuits
I
BQ
=
(
V
THEV
–
V
BE
)
/
(
R
THEV
+
(β + 1)R
E
)
where I
BQ
is the Base Current of the BJT
I
CQ
= β
×
I
BQ
Quiescent Collector Current I
CQ
equals the
Base Current multiplied by Beta
Figure-2: Voltage-Divider Bias circuit equations continued:
I
EQ
= I
CQ
+
I
BQ
where I
EQ
is the Quiescent Emitter Current
V
CEQ
=
V
CC
–
I
CQ
×
R
C
–
I
EQ
×
R
E
where V
CEQ
is the Quiescent Collector to Emitter
Voltage
V
C
=
V
CC
–
I
CQ
×
R
C
where V
C
is the DC Collector to Ground Voltage
V
E
=
I
EQ
×
R
E
where V
E
is the DC Emitter to Ground Voltage
V
B
= V
E
+
V
BE
where V
B
is the DC Base to Ground Voltage
The following equations apply to
Figure-3: Common-Emitter Amplifier with Voltage-Divider
Bias
, which is part of the Laboratory Experiment Procedure:
Use the value of the Quiescent Emitter Current (
I
EQ
) found for
Figure-2
: Voltage-Divider Bias to
calculate the small signal equivalent ac resistance (r
e
) of the emitter diode of the
transistor:
r
e
= (26 mV)
/
I
EQ
The ac voltage gain A
V
can be found
approximately
from the equation that follows for the
Common-Emitter Amplifier with Voltage-Divider Bias
of
Figure-3
:
A
V
=
– R
C
/
(
R
E
+ r
e
)
The denominator is the
sum
of R
E
(the nominally 390 Ω resistor in this experiment) and the
small signal equivalent ac resistance r
e
of the emitter diode of the
transistor itself.
The following equations apply to
Figure-4: (Collector) Voltage Feedback Bias Circuit
, which is
part of the Laboratory Experiment Procedure { un
like the "other" biasing circuits where the
Quiescent current through R
C
is I
CQ
, the resistor R
C
in a (collector) voltage feedback bias circuit
carries the current (I
CQ
+ I
BQ
)}:
I
BQ
=
(
V
CC
–
V
BE
)
/
(
R
B
+
(β + 1)(R
C
+ R
E
))
QCC
ECET
John Buoncora
Page 17
BJT Emitter Stabilized Bias, Voltage-Divider Bias, and (Collector) Voltage Feedback Bias Circuits
I
CQ
= β
×
I
BQ
Quiescent Collector Current I
CQ
equals the
Base Current multiplied by Beta
I
EQ
= I
CQ
+
I
BQ
where I
EQ
is the Quiescent Emitter Current
Figure-4: (Collector) Voltage Feedback Bias circuit equations continued:
V
CEQ
=
V
CC
–
(I
CQ
+ I
BQ
)
×
R
C
–
I
EQ
×
R
E
where V
CEQ
is the Quiescent Collector-Emitter voltage
V
C
=
V
CC
–
(I
CQ
+ I
BQ
)
×
R
C
where V
C
is the DC Collector to Ground Voltage
V
E
=
I
EQ
×
R
E
where V
E
is the DC Emitter to Ground Voltage
V
B
= V
E
+
V
BE
where V
B
is the DC Base to Ground Voltage
QCC
ECET
John Buoncora
Page 18
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