1
Table of Contents
1. Abstr Abstract…… act………………………… ……………………………………… …………………………………… ………………………… ……… ……………..2 2. Intro Introducti duction………… on…………………………… …………………………………… …………………………………… ………………… …………….2 3. Compo Component nents…………… s……………………………… ……………………………………… ………………………………… …………… ……………..3 a.
b.
c.
d.
e.
Transformer 4 Bridge Rectifier 5 Transistor as a switch 6 Battery 6 Load
6
2
4. Wo Working… rking…………………… …………………………………… …………………………………… ……………………………… …………… ………………7 5. Applica Applications tions………………… …………………………………… …………………………………… …………………………… ………… ……………..12 6. Conclu Conclusions sions…………………… ……………………………………… …………………………………… ………………………… ……… ……………..13 7. Refere References nces…………………… ……………………………………… …………………………………… ………………………… ……… ………………14
220 to 12 V D.C POWER SUPPL S UPPLY Y & STORAGE
1. Abs Abstra tract: ct: This project is to create a 220 A.C to 12V DC power supply that can also store the power for a long time. The circuit used is an efficient one and has brought many improvements into current D.C power supplies such as voltage regulation and removal of ripples in output. The 220 A.C voltage is first converted into 12 V A.C by a step down transformer, then a full wave rectifier bridge (based on wheat stone bridge) is used to convert the A.C into D.C. Then this output is filtered twice by two mechanisms. i.
In order to remove the ripples in the waveform of the bridge circuit.
3
ii.
Create a regulated and efficient power supply. supply.
A NPN transistor with a base connected to the Zener diode is also used as a switch in the circuit. Then 12 V is received as output voltage. The circuit s and waveforms are created using PSpice. Due to the voltage voltage regulation regulation and removal removal of ripples ripples in the output this power supply can also be used as a “battery eliminator” [6] which provides constant and efficient output to the load without the need for a battery. battery.
2. Intro Introduct duction: ion: The need of D.C Power supply is always there in the field of electrical engineering. The main advantages these D.C power supplies bring are portability and cost effective effectiveness ness as compared compared to A.C power power supplies supplies but sometimes sometimes the cheapness cheapness of these D.C power supplies results in the lack in efficiency of the output. That is the output of most of the D.C power supplies present in the market has ripples in it and is not pure pure D.C. D.C. Moreov Moreover er the output output voltage voltage is not exact exact due to losses losses in the circuit. To remove these draw backs in D.C power supplies we have made an efficient circuit that not only only removes the ripples in in the output voltage to make a pure D.C signal signal but also also regula regulates tes the voltage voltage to a consta constant nt and desired desired value. value. This is achieved by using a filter circuit and transistor which is used as a switch. We have used a bridge rectifier instead of two diode rectifier (which also produces full wave rectif rectifica icatio tion) n) becaus becausee the bridge bridge rectif rectifier ier does does not requir requiree a high high “peak “peak invers inversee voltage” as it utilizes most of the windings of the transformer. We have also used a simp simple le tran transfo sforme rmerr inst instea ead d of cent center er tap tap beca becaus usee it is chea cheape perr and and prod produc uces es compact and cheaper power transmission. The use of a RL circuit as a filter has improved the efficiency of the circuit by removing the ripples in the D.C that is rectified by the bridge. The use of transistor as a switch has brought the other improvement in the circuit I.e. it has regulated the voltage to a constant value that has saved our load from voltage fluctuation damages. Rechargeable Nickel Metal Hydr Hydrid idee batt batter erie iess are are used used,, whic which h are are bein being g used used exte extens nsiv ivel ely y in cons consum umer er electronics these days. These also have lower charging time and are very long lasting. Due to the efficient combination of the values of the circuit elements a
4
variety of loads can be attached to the output circuit i.e., any circuit element ele ment having voltage 12 V and resistance greater than 10 Ωs.
(The Circuit Diagram is placed on the next page)
5
6
3. Com Compon ponent ents: s: a.
Transformer[2]:
This is a step down transformer that converts 220 V A.C into 12 V A.C. A.C. A maximum current of 1200mA can flow through it and it works on a frequency of 50 Hz and it is easily available in market in low cost. It is not a center tap transformer and it is easy to connect it into the circuits to get actual and desired results, as required. S t e p D o w n T r a n s f o rm e r
220-12 V
7
The relation between number of turns and voltages of input and output coils is:
Vs/Vp =Ns/Np We have Vs= 12 Vrms and V p= 220 Vrms Then
Ns/Np=.054 The principle of the transformer is mutual induction. [2] The output of the transformer is pure 12 V A.C in this project.
b. Bri Bridge dge Rec Rectif tifier ier:: The rectification is conversion of A.C into D.C with the help of Diodes. There are two types of rectifications a. Half Half wave wave rect rectif ific icat atio ion n b. Full wave rectification We use Full F ull wave rectification by using bridge rectifier. This rectifier consists of four diodes (D 1, D2, D3, and D4) connecting each other as shown in figure:
D 5 1
4
-
+
2
The advantage of bridge rectifier over two diode rectifier r ectifier is that:
8
1.
2. 3.
Peak inverse voltage of bridge rectifier is very low as compared to the two diode rectifier. Power dissipation of bridge rectifier is lower. lower. The output of bridge rectifier is very efficient than two diode rectifier. Due to these advantages we have used bridge rectifier in our circuit. Principle of bridge rectifier is based on wheat stone bridge. The output of bridge rectifier is pure D.C (+12 v). That can be shown by connecting a resistance at its output terminals. This D.C output has ripples which are not a (Figure.3)
pure D.C . These ripples can be removed by connecting a capacitor which acts as a filter. c.
Tran ans sis to tor r as a s a sw swit itc ch[3]:
The transistor, having a Zener diode at its base is used in this circuit as a switch. The transistor works in an active region that is its base-emitter junction is in forward bias and collector-base junction in reverse bias. The transistor used in our circuit is shown in the figure: 2 N 2 2 22 A
Z e n e r 1 3 V
d. Ba Batt tter ery: y: We have used Nickel Nickel Metal Hydride Hydride (Ni-MH) (Ni-MH) rechargea rechargeable ble cells in this project instead of a 12 V battery as it is very cheap. Each cell has 1.2 Volts so we have added 10 cells in series to make 12 V storage.
V= V1+V2+V3+V4+V5+V6+V7+V8+V9+V10 V= 1.2+1.2+1.2+1.2+1.2+1.2+1.2+1.2+1.2+1.2 V=12 volts
9
e. Load: The loads connected in the circuit can have resistance greater than 10 Ω. As our transformer has maximum current rating of 1200mA and our Voltage is 12 V so by Ωs law:
R=V/I R=12/1200m R=10 Ω
4. Work orking ing:: The process of the getting a 12 V D.C from 165 V to 285 V A.C Is divided into following steps: 1. A step down Transformer is used to convert 220 V A.C into 12 V A.C. This is done by mutual induction phenomena in the transformer. The 220 v A.C input waveform is shown below:
10
(Figure.1)
The 12 V A.C stepped down output waveform of transformer is shown:
11
(Figure.2)
2.
In this step the full wave rectification is done. That is conversion of 12 V A.C into D.C. Bridge rectifier is used for this purpose. When the positive positive half half cycle cycle of A.C wave form reache reachess the upper upper termin terminal al of the bridge bridge rectifier this terminal becomes +12 V and lower terminal becomes -12 V with respect to upper terminal. Then diodes D 3 and D2 become forward biased and conduct while D 1 and D4 become reverse biased. The current flows from this path ( D2 to D3). This + half cycle cycle is observed observed at the output output of bridge bridge rectif rectifier ier.. Now when when Negati Negative ve half half cycle cycle reache reachess the upper upper terminal terminal of bridge bridge rectifier rectifier the lower terminal terminal becomes becomes positive positive with respect to upper terminal and diode D 1 and D4 conduct and current flows through this path (D 1 and D 4) while diode D 3 and D2 are switched
12
off. This Negative Negative half cycle is converted converted to positive half cycle at the output as shown below (by red wave):
(Figure.3)
3.
In the previous step the D.C waveform is not pure because it has ripples which are not suitable for our circuit. So these ripples can be removed by connec connectin ting g a filter filter circui circuitt at the output output of bridge bridge rectif rectifier ier.. This This filter filter contai contains ns a capaci capacitor tor in parall parallel el with with a resisto resistor. r. This This capaci capacitor tor has a suitable value that can be calculated by some mathematics which is very important in calculating the time constant of the capacitor (T).
T=RC T=2.13k X 4.7u T=10ms
13
Capacitor is charged after 5 time constants. So the ripples are removed by using this kind of capacitor. The output of the filter circuit is shown in red waveform where green is input of bridge:
(Figure.4) 4.
Up till now we have 12 V D.C waveform. Now the enhancement we have bro broug ught ht in this this circ circui uitt is the the use use of tran transi sist stor or havi having ng a Zene Zener r Diodec Diodeconn onnect ected ed to its base. base. It is used used as a switch switch as well well as 12 volts volts regulator. The biasing of the transistor is the major issue which could be solved by connecting D.C batteries but we solved this problem by using a resistor as a potential divider to avoid the use of batteries (an additional component of the circuit). Now the collector has voltage 12 volts and base has the voltage of 2.59 volts this makes the collector-base junction reverse reverse biased biased.. Initia Initially lly the bypass bypass capaci capacitor tor connec connected ted at emitte emitterr is unchar uncharged ged so the potent potential ial at emitte emitterr termina terminall of transis transisto torr is 0 volts. volts.
14
While the Zener Diode connected at base regulates 12 volts across itself so base-emitter junction becomes forward biased and capacitor begins to charge. This operation is called “switching of transistor”. After 5 time consta constants nts that that can be calcul calculate ated d by (T=RC) (T=RC) capaci capacitor tor become becomess fully fully charg charged. ed. When When the capaci capacitor tor is fully fully charg charged ed base-e base-emit mitter ter juncti junction on becomes reverse biased and transistor goes to cut off state. And all the voltage voltage is observed observed at this capacitor capacitor.. The output output wave form is shown below:
(Figure.5) 5.
This capacitor is now connected to our rechargeable battery. This battery is charged in approximately 120 minutes. The power stored in the battery is calculated as follows:
6.
P=VI
15
P=12 X 1200m P=14.4Watt The maximum load is connected to this battery is calculated (as in section 2.5). 2.5). So the maximum maximum load load which can be connect connected ed to this circuit circuit is greater than 10 Ω.
5. Applica Applications tions:: This circuit has many applications: a.
b.
c.
The circuit can be used as a “battery eliminator” [6] i.e. as it provides constant regulated voltage and ripple free output. It can be used to give output directly to a load instead of a battery first. This reduces the cost of battery. It can be used as Battery charger. charger. This can be detached from the circuit and then used to supply power to a variety of electronic devices. It can be used as a D.C voltage regulator which is capable of providing ripple free voltage.
d.
To recharge an electric vehicle (EV) battery pack [5].
e.
To recharge a fuel vehicle's starter battery, where a modular charger is used [5].
6. Concl Conclusion usions: s: We have made a storing power supply. supply. Which takes a 220 volts A.C input and steps steps down down and rectifi rectifies es it into 12 volts volts D.C output output and stores stores a power of 14.4 watt in the rechargeable battery which can be stored for as many days as you want? It has some major advantages over common power power suppli supplies es e.g., e.g., it uses uses a step step down down transf transforme ormerr instea instead d of center center tape, tape, bridge bridge rectif rectifier ier instea instead d of two diode rectifie rectifierr is used used and most
16
important important is transistor transistor followed followed by a Zener diode at its base acting as switch which prevents prevents damages due to false input as well as any any fault in output voltages. The power can be stored in battery for many days and Load should be greater than 10Ω.
7. Ref Refere erence nces: s: 1. 2. 3. 4. 5. 6.
Microelectronic Circuit by Sedra-Smith Power Electronics by McKenzie Awais Haider (
[email protected] (
[email protected])) www.pspice.com www.wikipedia.org http://en.wikipedia.org/wiki/Battery_eliminator
