INTERDISCIPLINARY CD-MATH)

UNIT;ECE 2100 ELECTRONIC WORKSHOP

LAB REPORT 4 13/NOV/2024
INVESTIGATION ON POWER SUPLY 1

I N T R O D U C T I O N This

All electronic circuit need energy to work. In most cases, the energy
is provided by a circuit called the power supply. The power supply is a key
part of any electronic system, since it energizes the other circuits. A
power supply failure will affect all of the other circuits. The power supply
changes the available electric energy (usually alternating current-ac) to
the form required by various circuits within the electronic system (usually
direct current-dc). A power supply converts the ac voltage to a steady dc
level. The output signal is filtered to an accurate dc output voltage. This
dc voltage is automatically maintained through regulation. The most
common electrical power source is that furnished by the local power
company, and is alternating current at a frequency of 50 or 60 Hertz
(cycles per second). Batteries are also electrical power sources.

OBJECTIVES
To gain knowledge on circuit power connection.
To know more about electronic objects such as rectifier and diodes.
To gain knowledge on conversion of power from AC TO DV
BACKGROUND
Power supplies may be built or designed to meet certain requirements.
The four blocks of the power supply include: (1) transformer, whose
purpose is to step-up or step-down the alternating current voltage to levels
needed by the boom box, television, computer or other electronic circuits
of various electrical equipment or appliances; (2) rectifier, which is used
to change an AC input into a pulsating DC output; (3) filter, which is
needed to smooth out the direct current; and (4) regulator, which is used
to eliminate the decrease in output voltage of a power supply when a load
is applied. Figure 1 shows the six blocks of a dc power supply.

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ac Bridge Capacitive Zener dc

Transformer
Input Rectifier filter Regulator Load

Figure 1.
BLOCK DIAGRAM OF
POWER SUPPLY

Formulas are used in determining voltage regulation, filter capacity, etc.

Skills in algebra and other areas of mathematics are useful in utilizing the
formulas correctly.
A schematic diagram of the electronic power supply is shown in Figure 2.
This diagram indicates how the four blocks of Figure 1 are connected to
form the power supply. This ILAP is designed to provide experiences in
calculating values needed to design an electronic power supply.

PREREQ UISITE SKILLS

1:TRANSFORMER
A transformer is included to step the ac line voltage up or down to a
desired value. For most electronic equipment a voltage of less than 115
volts is required, and therefore a step-down transformer is needed. The
transformer consists of two or more coils ( a primary winding
and secondary winding) linked together by magnetic flux. A step-down
transformer’s primary voltage is greater than the secondary voltage. If the
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UNIT;ECE 2100 ELECTRONIC WORKSHOP
LAB REPORT 4 13/NOV/2024
INVESTIGATION ON POWER SUPLY 3
primary winding turns exceed the secondary turns, the transformer steps
the voltage down.
In the design of the power supply one should be able to determine the
secondary voltage mathematically using the following relationship for an
ideal transformer:
Vpri Npri Isec
= = (1)
Vsec Nsec Ipri

Where
N = number of turns,
V = voltage in volts, I =
current in amps, pri =
indicates primary, and sec
= indicates secondary.

The concept of turns per volt will be used in modifying the secondary
voltage for the design of an electronic power supply.
2:RECTIFIER
A diode is a semiconductor device that exhibits full-wave bridge rectifier (or
simply bridge rectifier) uses four semiconductor diodes. The
characteristics that lie between those of insulators and conductors. Silicon
is the most extensively used semiconductor material for diodes. When the
diode is forward-biased (connected to conduct or behave like a conductor)
it acts like a closed (on) switch which will permit current to flow. On the
other hand, when the diode is reversed-biased (characteristics like an
insulator), it acts like an open switch (off). A forward-biased silicon diode
acts as a closed switch with a small voltage of 0.7 volt barrier potential.
Germanium, another semiconductor material used for diodes, has a barrier
potential of 0.3 volt.
The full-wave bridge rectifier is the most commonly used type of rectifier
circuit used in dc power supplies. Operation of the bridge requires the
forward-bias of two of the diodes. Diodes D2 and D3 conduct during the
positive half-cycle of the input from the transformer. The remaining two
diodes do not conduct. With the negative half-cycle, diodes D1 and D4
conduct while D2 and D3 do not conduct. This is shown in Figure 2. The
bridge, in short, switches both half-cycles at the input (a full wave )
through to the output in only one direction. However, by applying a
negative voltage across the diode, it will be reverse biased and carries
almost no current. If this negative voltage increases to the certain amount
(breakdown voltage), the diode would go into breakdown. This voltage is

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known as the peak inverse voltage (PIV).

PIV = Vpeak (out) + 0.7 (3)

3:FILTER

In electronic circuits. A signal closer to pure direct current bridge rectifier

converts an ac signal to a pulsating dc output. This pulsating DC output is
not usable for most is required. Pulsating direct current contains an AC
component which is undesirable for the output of a power supply.
The component in the power supply is called ripple and must be removed
for most circuit applications. A filter circuit is used to remove the ripple
and provide an unvarying dc voltage. A common technique used for
filtering is the capacitive filter. Capacitors are devices which store energy
in the form of a charge and then later deliver that charge to a load.
The capacitor filter provides a nearly smooth (straight line) dc output
voltage from the filter. A capacitor connected across a rectifier output
quickly charges at the beginning of a cycle and slowly discharges after the
positive peak. Variation in the output voltage due to the capacitor
charging and discharging is called the ripple voltage. Furthermore, ripple
factor (r) can be defined by comparing ripple voltage (Vr p-p) to the dc
value of voltage(Vdc). Figure 3 shows the relationship between ripple and
dc voltages.

Vc

V r(p – p)

Figure 3.
THE RELATIONSHIP
BETWEEN THE FULL-WAVE

t RECTIFIER VOLTAGE
Vm Vdc (DOTTED LINE) AND
T FILTERED OUTPUT
VOLTAGE (SOLID LINE).

The following equations can be used to calculate ripple voltage, dc

voltage, and ripple factor.

Vm = Vpeak (sec) −1.4

)
V r ( p − p )
r =
V dc
(7)

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UNIT;ECE 2100 ELECTRONIC WORKSHOP
LAB REPORT 4 13/NOV/2024
INVESTIGATION ON POWER SUPLY 5
Where

Vm = peak rectifier voltage (volts),

Vdc = filtered dc output voltage (volts),

Vr (p-p) = peak-to-peak ripple voltage (volts),

RL = load resistance (3),

r = ripple factor, f =

frequency (Hz), and

C = Capacitance (Farad).
The amount of ripple across a filter can be further reduced by using an
additional RC filter section as shown in Figure 4. The purpose of RC
section is to pass most of the dc component while attenuating the ripple
voltage.

Vr Vr
Vdc Vdc

t t

R
Transformer Bridge
Rectifier

Figure 4. C1 C2
BRIDGE RECTIFIER AND FILTER
CIRCUIT.

Requirement 3.1.
Requirement 3.2.
Prepare a written techn
4:REGULATOR

The REGURATOR will increase the variation of the rectifier output volt
of DC signal produced with rectifier and filter has a small ac ripple
. Furthermore, varying the load resistor across the ter-

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minal of the power supply will change the voltage level. To overcome all
these problems, a Zener diode can be used as shown in Figure 2. The
characteristic curve of a Zener diode is shown in Figure 5.
The parameters of the Zener diode curve are defined as follows:
VZ = Zener breakdown voltage (volts), IZM

= Zener maximum current (Amp), and IZK

= Zener knee current (Amp).

VZ
0
VR

IZK

IZM
Figure 5.
CHARACTERISTIC CURVE
IR FOR ZENER DIODE

Since the Zener diode and load resistance are in parallel, the voltage
across them must be the same.( See Figure 2.) Applying the voltage
divider rule, the following relationship is obtained.

RL
VZ = VL = Vdc( ) (8)
RL + R1
The following relationships will allow us to find the maximum load
resistance:

VR1 = Vdc −VZ

V
IR 1 = R1

R1
It is assumed the filtered output voltage,Vdc, is fixed, while the load resistance varies. We seek to
determine the minimum load resistance that will turn the Zener diode on (maintain regulation). The
Zener breakdown voltage VZ ( which remains constant over the range of current values), Zener maximum
current IZM, and Zener knee current Izk are 10V, 15mA, and 1mA respectively. The resistance value for R1
is assumed to be 1 kΩ and the dc voltage, Vdc, provided by filter stage is equal to 30V.

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UNIT;ECE 2100 ELECTRONIC WORKSHOP
LAB REPORT 4 13/NOV/2024
INVESTIGATION ON POWER SUPLY 7

COMMENTS
Power supply system in electric circuit provide suitable frow of elect current in electronic gadgets and
mostly that connected to a AC power.But in all, there is disadvantage and advantage if this system
Advantage
They are small in size and weight
They have high efficiency
They provide flexible line voltage and frequency

Disadvantage
They are expensive
They are more complicated
CONCLUTION
The power supply system is a useful system in electronic gadgets. It helps in power
regulation and control of voltage and current required by gadget.This makes frequent
and easy usage of electrical things.

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REFERENCES

1. Bogart, Theodore F., Jr. Electronic Devices and Circuits. Third Edition.
New York: Macmillan Publishing Company, 1993.
2. Boylestad, Robert and Louis Nashelsky. Electronics: A Survey. Third
Edition. Englewood Cliffs: Prentice Hall, 1989.
3. Floyd, Thomas L. Electronic Devices. Fourth Edition. Englewood Cliffs:
Prentice Hall, 1996.

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