AL-Asmarya Islamic University

Faculty of Engineering-Electrical and Computer Engineering

Department

ECE321 Electronic Lab

Report 5:

The DC Power Supply Project

Name student:
Mohammed farhat AL-Tagore
R. Number:
8117010
Name doctor:
D. Salem Al-Hemmaly

Autumn 2021/2022

1
Abstract

A power supply is a device that supplies electrical energy to one or more electric loads. The
term is most commonly applied to devices that convert one form of electrical energy to
another, though it may also refer to devices that convert another form of energy (e.g.,
mechanical, chemical, solar) to electrical energy. All electronic circuits from simple transistor
and op amp circuits to elaborate digital and microprocessor systems require one or more
sources of DC voltage. Simplest supply is a dc battery. It is not an ideal one as its terminal
voltage changes in accordance with load due to its internal resistance. Electronic
components require a DC supply that is well regulated, has low noise characteristics and
provides a fast response to load changes. The present report exposes the way that was
design a 120V rms to 12V DC by NI multisim software, It will present the calculations to
obtain the power supply, components, as well as the justification on the way that was made.

Table of contents
Table of figures………………………………………………………1
1 Introduction................................................................................3
1.1 Transformer.......................................................................................3
1.2 Rectifier.............................................................................................4
1.3 Filter..................................................................................................4
1.4 Voltage Regulator..............................................................................4
2 Calculations and design...............................................................4
3 Results and discution...................................................................7
4 Conclusion...................................................................................8
5 Reference....................................................................................8

Table of figures
Figure 1 Block diagram of power supply...................................................................................2
Figure 2 full bridge rectifier......................................................................................................3
Figure 3 The secondary side wave............................................................................................4
Figure 4 The output of rectifier.................................................................................................4
Figure 5 The waves C and R-C filters.........................................................................................5
Figure 6 The 12V DC power supply circuit................................................................................5
Figure 7 The wave of Vripple....................................................................................................6

2
1 Introduction

Virtually every piece of electronic equipment is powered from a low voltage DC supply. This
source will be either a battery, a combination of battery and DC/DC converter or a power
supply converting AC mains into one or more low voltage DC supplies, suitable for electronic
components. AC power supplies, and most DC/DC converters, also provide isolation from the
.input to the output for safety, noise reduction and transient protection
When we want to design a power supply, we need to know the final application of it
because, according to this, it will be convenient make a linear or switched power supply
Here we are going to make a linear power supply. This kind of power supply consist of
several stages. In the first one we receive an alternating current input, which we reduce the
amplitude and we magnetically isolate using a transformer, then, by rectifiers, we convert
the alternating current in to direct current. After this, we filter the signal to a dc level and
finally, we use a zener diode to obtain a desired fixed dc voltage. This voltage keeps at the
same level even if the dc input voltage varies or the output load changes. These stages are
.represented in the block diagram of the figure 1

Figure 1 Block diagram of power supply

.Let RL=100Ω

1.1 Transformer

The ac in will depend of the region in that the power supply will be use. In Mexico, the
alternating current signal of the home networks is 120VAC@60Hz, knowing this, we must
consider use a right transformer, because, we want a suitable ac voltage in the secondary of
.the transformer for the realization of the power supply

3
1.2 Rectifier

.The rectifier circuits take care of convert the AC voltage in to DC voltage

There are many types of these, the most common is the full-wave rectifier, and there are
two types of this: middle bridge rectifier and full bridge rectifier. in this report we will use
.full bridge rectifier

Figure 2 full bridge rectifier

1.3 Filter

One of the most used filters is the capacitive filter. This one consists of a capacitor at
the output of the rectifier, will See that, when the capacitor is
disconnected, the output of the rectifier has a considerable ripple and, when a capacitor is
.connected, this ripple will decrease

1.4 Voltage Regulator

We choose voltage of to use one 12 V Zener diode works on the pregnancy at any
unexpected change in the value of the current ,Any works as proven to the effort on
.pregnancy

2 Calculations and design

1. By Multisim software we connect a transformer between the two

terminals of 120v rms voltage source (look at circuit in figure 6), The ratio
between the primary side to the secondary side of the transformer is
10:1.
Np/Ns=10 Then Vp/Vs=10
Vs=12Vrms

4
 Figure 3 The secondary side wave

2. Now we connect a full wave rectifier between the two terminals of the
transformer as in figure 6. By using oscilloscope we get the output of
rectifier as following:

Figure 4 The output of rectifier

3. We notice from the previous figure that the ripple is very large, so we
need a filter to reduce the ripple to less than 2%. We will use RC filter. We
can calculate the capacitor value by the following relationship:
C>=Idc/(Vripple*f)
Idc=IL=VL/RL=12/100=0.12A
Vripple=12*2/100=0.24
C>=0.12/(0.24*120)=4.1667mF
C=5mF

5
 The output after the capacitor will be as in the following figure (the upper
curve), so we need a resistance to reduce the thrust voltage and thus
reduce the ripple as well and this is useful, the resistance is calculated as
follows:
VR1=Vp -Vdc=14.7817-12=2.7817V
R1=VR1*IL=2.7817*0.12=23.18ꭥ
Let R1=20ꭥ
After connecting the resistance in series with the capacitor, we get the
output as in the following figure (lower curve). Notice that the ripple is
becoming less.

Figure 5 The waves C and R-C filters

4. We connect a voltage regulator in parallel with the filter, We use a zener

diode BZX55C12 as a regulator. The polarity should be as in figure 6.
5. After performing all the previous steps we get the following circuit:

T1 D3
V2 R1
120Vrms
60Hz 20Ω
10
0° 3N246 C2 D1 RL
5mF BZX55C12 100Ω

Figure 6 The 12V DC power supply circuit

6
3 Results and discussion

1. If we use a transformer with VPeak on the secondary side is 12 + 0.75*2

(rectifier voltage), we will not need the resistance R1.
2. It is necessary to check the polarity especially when connecting the zener
diode, capacitor and rectifier.
3. Note that initially it takes some time to charge the capacitor before the
voltage stabilizes at 12V and the reason for the delay is that we put two
large capacitors in parallel.
4. The zener diode has low efficiency currents .it is because if the load
current is large .there will be considerable power loss in the series limiting
resistance .
5. One problem with zener diode stabilizer circuit is that the diode can
sometimes generate electrical noise on top of the DC supply as it tries to
stabilize the voltage.
6. The next figure explain The Vripple.

Figure 7 The wave of Vripple

Notice: Vripple=12.02-11.90=0.12v

7. The voltage on RL in design circuit equal 11.979V then the circuit has
error:
Absolute error=11.979-12=-0.021v
The percentage of absolute error=100%*0.021/12=0.175%
If we decrease R1 get a larger value of the output VL.
8. The resistor RL value will be called the full load. In order to calculate the
regulation percentage, you would use the following formula:
𝑅𝑒𝑔𝑢𝑙𝑎𝑡𝑖𝑜𝑛 % = [𝑉(𝑛𝑜 𝑙𝑜𝑎𝑑) − 𝑉(𝑓𝑢𝑙𝑙 𝑙𝑜𝑎𝑑) ]/𝑉(𝑛𝑜 𝑙𝑜𝑎𝑑)

7
 = [12.133 − (11.979)] /12.133 = 1.27%
This means that there is not much of a change in our voltage level when
you vary the load resistance.

4 Conclusion

One of the most important sections of every dispositive we use is the power supply. This is
the responsible of power the circuits that make our devices work, and on this depends the
useful life of many dispositiveS . That’s why the design of the power supply must be done in
the better way. After design this power supply we realized of how complex could be
designing a good power supply. There is lot of things to consider, since the characteristics of
the input and the output, to how efficient must be. Also, we are amazed with how useful the
courses of our career have been. The mathematical basis and all the circuits theory helped
with the problems we must solved on the design, and, of course, the simulations that we
made here were very useful to know if we were in the right way. Anyway, the objectives set
at the beginning of the project were achieved and the prototype of the power supply work
properly and according to the characteristics we set.

After all work we did on our project we have learned so many things :
1. We always see A DC power supplies in laboratories and a DC charger for example
for mobiles, laptops, cameras and so many things…
It is the first time we learnt about its major stages.
2. it is the first time that we deal with transformer in these details .
3. we have studied the rectifiers in Power Electronics course but it is the first time we
see the output at the oslliscope by our work.
4. It is the first time we deal with many IC’s we studied in many courses like(filters,
rectifiers ,zener diodes ,etc....).

5 Reference

1. Fundamentals of Electric Circuits Charles K. Alexander | Matthew n. o. Sadiku.

2. Online tutorial: Rectifiers Simulation with Scope instrument .

3. Peter ,Kurscheidt , leistungs elektronik,1977.
4. Power electronic books (Mohammad Rashid).