I.
Discussion of theory
Amplifier is the generic term used to describe a circuit which
increases its input signal, but not all amplifiers are the same as they
are classified according to their circuit configurations and methods of
operation.
In “Electronics”, small signal amplifiers are commonly used
devices as they have the ability to amplify a relatively small input
signal, for example from a SENSOR such as a photo-device, into a
much larger output signal to drive a relay, lamp or loudspeaker for
example.
There are many forms of electronic circuits classed as amplifiers,
from Operational Amplifiers and Small Signal Amplifiers up to Large
Signal and Power Amplifiers. The classification of an amplifier
BJT Voltage
Audio Input Divider Bias Darlington
Signal Configurati Connection
on
Output
Sound
depends upon the size of the signal, large or small, its physical
configuration and how it processes the input signal that is the
relationship between input signal and current flowing in the load.
Block Diagram
Input Signal
For the input of these amplifier, sound wave are acquired through
different mobile devices or any digital sound.
BJT Voltage Divider Bias
The common emitter transistor is biased using a voltage divider
network to increase stability. The name of this biasing configuration
comes from the fact that the two resistors RB1 and RB2 form a
voltage or potential divider network with their center point
connecting the transistors base terminal directly across the supply.
This voltage divider configuration is the most widely used
transistor biasing method, as the emitter diode of the transistor is
forward biased by the voltage dropped across resistor RB2. Also,
voltage divider network biasing makes the transistor circuit
independent of changes in beta as the voltages at the transistors
base, emitter, and collector are dependent on external circuit values.
Darlington Connection
One transistor circuit configuration that can be used to very good
effect in many instances is the Darlington Pair. It normally consists of
two transistors. The emitter of the input transistor is connected
directly to the base of the second. Both collectors are connected
together. In this way the base current from the first transistor enters
the base of the second.
The Darlington transistor pair is a very useful circuit in many
applications. It provides a high level of current gain which can be
used in many power applications. Although the Darlington pair has
some limitations, it is nevertheless used in many areas, especially
where high frequency response in not needed. In particular
Darlington transistors are used for applications including audio
outputs, power supply outputs, display drivers and the like.
II.
Schematic Diagrams
R1
8kΩ
R4
200Ω
R5
8.5kΩ
C4
Q1
D2
1N4148
500µF
C3
V1
24V
470µF
V2
R2
806Ω
500mVrms
1kHz
0°
R8
1kΩ
Q3
D1
1N4148
TIP31A
C1
2N3904
470µF
R6
806Ω
R3
100Ω
Q4
2N3904
R7
100Ω
Q2
TIP32A
(PCB layout design)
III.
Materials
 Printed PreSensitized P.C.B.
(4x6)
 Acrylic Glass
(CASE)
 Transistor
o TIP31A
Speaker
8Ω
o TIP32A
o 2N3904
 Zener Diode
(1N4148)
 Resistors
o 8KΩ (3) ,
1KΩ ,806Ω
(2), 200Ω,
100Ω (2)
o
 Capacitor
o 470µF (3)
 Potentiometer
 Power Switch
 3.5mm Audio
Receptacle
 Drill and Drill Bit
 Lead
 Ferric Chloride
IV.
V.



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
Procedures

1.)
Prepare the materials needed in making the amplifier

2.)
Create a schematic diagram (Darlington Connection)

3.)
Test the schematic diagram in a breadboard to see if
it is working.

4.)
Convert the schematic diagram to ultiboard for
etching.

5.)

6.)
Drill the Pre-Sensitized P.C.B according to the holes
presented in the ultiboard.

7.)
Place the components and solder it.

8.)
Place the finished work in acrylic glass case
Etch the Pre-Sensitized P.C.B.

Data and Results

R1
8kΩ
R4
200Ω
C4
Q1
R5
8.5kΩ
D2
1N4148
500µF
C3
V1
24V
470µF
R2
806Ω
V2
500mVrms
1kHz
0°






Q3
D1
1N4148
TIP31A
C1
2N3904
R3
100Ω
Voltage Divider
 Configuration

R8
1kΩ
470µF
R6
806Ω
Q4
2N3904
R7
100Ω
Q2
TIP32A
Darlington
Speaker
8Ω
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

Our circuit is mainly composed of transformer, rectifier, filter
and voltage regulator to achieve our desired output voltage of 18
VD.C. .

The first stage is the transformer. Our group used a coil ratio
of 9:1 with a 1A capacity and basically reduce a 220V to 24V. We
decided to use this transformer because it is commonly available in
the market and close in our desired output for us to regulate easier.
 After stepping down a high voltage input, a bridge type rectifier
circuit is present to convert an A.C to D.C. voltage. We decided to use
this because the rectification efficiency of full-wave rectifier is double
of that of a half-wave rectifier. Similarly we use a four highly reliable
and small-sized silicon diode in order to create the rectification.

The output from a rectifier circuit is technically isn’t stable.
That’s where filtering comes. The pulsing current cause by an A.C
source isn’t suitable for most electronic circuits. Filtering is usually
accomplished by introducing a capacitor into the power supply circuit
and our group used 470 and 47µF.

Lastly, we add a Zener diode to regulate our desired output.
Its function is to provide a constant output voltage to a load
connected in parallel with it in spite of the ripples in the supply
voltage or the variation in the load current and the Zener diode will
continue to regulate the voltage until the diodes current falls below
the minimum IZ(min) value in the reverse breakdown region. Hence,
our group use 1N4471 Zener diode that regulates at 18V constantly.

XMM1
XSC1
Ext Trig
+
XMM3
_
B
A
+
V1
220Vrms
60Hz
0°
T1
9:1
D1
D2
R3
1N4001
1N4001
1kΩ
D3
D4
1N4001
1N4001
XMM2



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
C1
470µF
C2
47µF
R1
5kΩ
_
+
_
D5
1N4471
R4
2kΩ

OSCILLOSCOPE READING



At the first stage of simulation, the reading of the
multimeter after the transformer is 24.47VD.C and it has no
discrepancies in comparison with the calculated value which is
24.44VD.C. Nonetheless, it is 1/9 of the input voltage.

Moreover, the voltage at the rectified circuit is 22.872V D.C.
The voltage is subtracted by the threshold voltage of the two forward
biased diode at both alternation. Hence, the calculated value of
23.044VD.Cand has a percentage error of 0.75 .

the
Thefiltered circuit has a voltage reading of 32.771V D.C and
true is 32.537VD.Chaving a percentage error of 0.72 .
Nonetheless, the approximate ripple voltage at the output is
and the resulting ripple factor is
0.32
0.105 V
which suggest more effective
filtering.

Lastly, the Zener diode has a value of 18V and with the
32.54VD.Cas an input voltage, the maximum and minimum R Lis
33.33kΩ and 1238Ω respectively. Our group used a 2000Ω resistor
that is sufficient to activate the Zener diode and to have a constant
output of 18VD.C. . Nevertheless, the output voltage at the simulated
circuit is 17.923VD.C and have a percentage error of 0.43 .

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VI.
COMPUTATION:

Av =


B=
Ic
Ib

B=
14.059 mA
70.087 µA
−R 1‖ R2‖ Rc ‖Bre
ℜ

IE=Ic

ℜ=
26 mv
14.059 mA

ℜ
=1.85Ω
Avvd =

−1
÷ 1.85
1
1
1
1
+
+
+
8000 806 200 200 (1.85)

Avvd=-59.61

Pout=0.25IcsatVcc

Icsat=
Vcc
RL

Pout=0.25(

Pout=18W

Pdc=
24 x 24
)
8
IcsatxVcc
π
2



Pdc=
Vcc
πRL
Pdc=
24 2
π (8)
Pdc=22.92W

eff =
eff =

18
×100
22.92

Eff=79%






Conclusion

With the design made and the circuit tested, the group
concludes that a power supply produce a constant voltage output
through the proper combination, connection, and configuration of
resistors, diodes, capacitors and a transformer with an appropriate
value rating.

With it, the group concludes that a transformer may
either step down or step up the input voltage for the required output.
In connection to this, the group also concludes that in a power supply
design, a bridge type diode configuration is the best to use in order to
convert an ac input into a rectified dc output.

In a transformed dc output, the group concludes that
capacitors are used in the circuit in order to maintain a constant dc
output. In line to it, the group can say that the higher capacitor value,
Po
× 100
Pdc
the longer the time the capacitor to be charge thus having an output
the output that gradually approach a consistent value. Similarly, a
lower capacitor value will have a faster charging time and abrupt
voltage output but a lesser consistent one.

In order for the power supply to produce the desired
output, the group concludes that a regulator must be used to attain
the voltage needed. The group concludes that a Zener diode
maintains the output leaving it with respect to its voltage rating. The
group also concludes that resistors play an important role in keeping
the current and voltage in an optimum safe value for the circuit.

With the project done, the group concludes that
polarity, connection, configuration and mathematical values are the
most important thing to consider in designing a power supply.
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Documentation
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