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ISTANBUL TECHNICAL UNIVERSITY
DEPARTMENT OF ELECTRICAL
ENGINEERING
POWER ELECTRONIC CIRCUITS
FALL 2008, CRN: 11473
ASST. PROF. DENIZ YILDIRIM
PROJECT REPORT
MINIPROJECT I
15 V DC Adapter
GROUP MEMBERS
040050348
040050441
040050410
Yunus Gündüz
Ali Çağlıyan
Ersin Köse
Electronics Eng.
Control Eng.
Control Eng.
SUBMISSION DATE: OCTOBER 23, 2008
Objective of Project
The objective of this project is to design a standart household AC/DC adaptor
which output must provide regulated 15 V DC at a load current of 0.5 A.
To build this circuit, firstly circuit elements must be obtained, secondly value of
circuit elements must be calculated.
Step 1 : Choosing the elements of Circuit
Up to the circuit diagram which has given before, elements of circuit are obtained and
settled on the diagram which is drawing in Figure 1.
Figure 1: Circuit diagram
Above diagram was drawn in PSpice Circuit Analyze Program. In this figure all the
components of circuit has drawn and ready for the analyze.
The differences between the main project there are extra elements such as the switch
witch make the regulator on/off easily by the user. The other extra element is the fuse
tube which keeps the circuit over current dangers.
Rest of the circuit element types is same as main project.
Step 2 : Calculating the values of elements
First of the circuit element is transformator which convert the voltage amplitude. This
element has been chosen 15W 220V/24V. Although the LM7815C device needs 20V
input value which is requirement of regulator and diodes, transformator has 24 V output
voltage because this is a standard, cheep and easy findable. Beside of that the reason of
choosing transformator as 15 W is provide the necessary power for load and the circuit
elements needs. It is fact that this value is a little bit higher then circuit needs but the
reason of choosing high capacity, transformator could be use any other project that might
will be required more power than this device.
Second of the circuit elements are diodes which are rectifying AC to DC. This
element was chosen D1N4001 model. This diode type is useful to project needs. For
example the forward voltage current (If) answer the circuit needs and forward voltage
drop value is convenient for device.
The other element of circuit is electrolytic capacity which is used for filtering. from
the formula which is taken from course notes,
∆V=Vm/2fRC;
C = Vm/ (2*f*R*∆V);
R’s value is approximately 30ohm. (parallel regulator resistance is ignoring because it
is much more bigger than 30 ohm)
∆V/Vm is should be less than 10%,
f is 50Hz.
Finally, minimum C value(ripple voltage=10%) is calculated as 1.1 mF so C is
chosen 2.2 mF 25 V electrolytic capacity because it is one of the standard values and
works properly with D1N4001 diode. It means when capacity charges, current do not
warm diode.
One of the other element of circuit are Blue Light Emitting Diode (LED) and Rled
(R1).LED is chosen a standard Blue Led which has voltage current (If) is 20mA and
forward voltage drop value 4V.So Rled value calculated as by using formula below,
Vi- Vled= Rled* If,
(Vi
is regulator input voltage)
So minimum value of Rled calculated as 900 ohm. However, Rled was chosen as 1.5k
to use LED safely.
One of the important element of circuit is regulator which makes output voltage as
stabile in 15 V. Regulator was chosen LM7815c because this model is cheap, easy to find
and its PSpice model is available on internet. There are also C1 and C2 capacitors using
parallel to regulator for filtering the input and output of regulator voltage. As indicated in
78** datasheets (*) C1 equals 220nF and C2 equals 100nF.
Process of the Adapter’s Building
There are four stages between input and output voltage.
Converting
amplitude
Rectifiying
Filtering
Regulating
.
~220VAC
15 VDC
By using 15 watt 220/24 transformator (TX1) amplitude of input voltage is
decreasing to 24V. Then by using four D1N4001 (D1, D2, D3, D4) diodes as bridge 24 V
Ac voltage is rectifying. After that up to parallel capacitor (C4) connected to the circuit
for filtering so ripple voltage become less than 10%. Finally, rectified input voltage and
current is stabled with regulator to make safe the DC output values in the regulating step.
There is also fuse lamp was used to make circuit more safe (Cutting the circuit into less
loads incident which occur wrong movements while experiment).
Simulations and Results
After calculating all values of components the circuit was settled in PSpice circuit
analyze program (Figure 1 ) and observe below results.
Figure 2: Red line shows regulator input voltage-Green line shows regulator output
voltage
As seem in the Figure 2 and Figure3 input voltage of regulator changes between
20.972V and 21.838V.
Figure 3: Red line shows regulator input voltage-Green line shows regulator output
voltage
This shows that,
∆V/ Vm=0.886/21.838=3.96% <10% which is as like as expectations.
Figure 4: Red line shows regulator input voltage-Green line shows regulator output
voltage
As seem in the Figure 4, curser shows the output of regulator voltage is 15.107 V
which is the almost same value with intended before.
Figure 5: AC current at the secondary side of transformer
As shows in Figure 5, these current peaks shows capacity is charging. In other times
since C4 voltage bigger than input voltage, capacity is discharging until these two voltage
value become same.
Results and Real Oscilloscope Prints of Circuit
Load
Current(A)
No load
0.05
0.10
0.15
0.20
0.25
0.3
0.35
0.4
0.45
0.5
Regulator input
current(A)
0,022
0,07
0,12
0,17
0,22
0,27
0,32
0,37
0,42
0,47
0,52
Pin(W)
2
3,7
5,4
7
8,4
10
11,5
13,2
14,8
16,4
17,5
Vcdc
32,75
32,13
31,40
30,74
29,94
29,15
28,32
27,43
26,72
25,80
25,00
Pdc
(W)
0,72
2,25
Pout
(W)
0
0,75
1,5
5,23
2,25
6,58
3
7,87
3,75
9,06
4,5
10,15 5,25
11,22 6
12,126 6,75
13
7,5
Table 1: Measurements Result
Circuit is tried and saved the above results.
Figure 6: Real regulator input voltage
Pout/
Pin
0%
20,30%
27,80%
32,10%
35,70%
37,50%
49,10%
39,80%
40,50%
41%
42,85%
Pout
/Pdc
0%
33,30%
39,80%
43%
45,60%
47,60%
49,70%
51,70%
53,50%
55,70%
57,70%
Figure 7: Real regulator output voltage
As seem in the Figure 6 and Figure 7 oscilloscope prints shows that circuit is
working properly. Prepared circuit has tested the load current values between 0 to 0.5A
and Table 2 and Table 3 has drawn via Excel with this values.
70%
50%
40%
Seri 1
30%
20%
10%
0.5
0.45
0.4
0.35
0.3
0.25
0.20
0.15
0.10
0.05
0%
No load
Pout/Pin
60%
Load current (A)
Table 2: Efficiency changing chart of Pout/Pi via Load current change
45%
Load Current (A)
40%
35%
30%
25%
Seri 1
20%
15%
10%
5%
0.5
0.45
0.4
0.35
0.3
0.25
0.20
0.15
0.10
0.05
No load
0%
Pout/Pi
Table 3: Efficiency changing chart of Pout/Pi via Load current change
These 2 tables above are simply said that the efficiency of circuit is increasing by
loading device because circuit is designed for 0.5 A. There is a fact that 47% efficiency is
not a good value for a converter device and there is a mistake which causing by 15 W
transformator. As mentioned before this device is expensive and experiment group maybe
need this power later experiments. Also 25 V is capacitor value is not proper for the
circuit. Reason of this mistake is before purchasing components group member calculated
Capacitor’s output DC voltage as 25 V however, after the experiment in no load
condition it seems that capacitor’s output DC voltage increase to 32 V. Consequently this
high value harms capacity in long use condition (Capacitor’s heat increase and finally
explode).
Finally all the measurements were making with a device called avometre which
includes Dc-Ac voltmeter, ammeter and also ohmmeter. Oscilloscope is used for observe
the voltage’s characteristics where different nodes of the circuit.
References

D1N4001 type diode datasheet from the web page ‘www.alldatasheets.com’

LM7805c type regulator datasheet from the web page ‘www.alldatasheets.com’

All formulas which use for the calculations are taken from Asst. Prof. Deniz
Yıldırım’s course notes.