How 12 Volts DC Power Supply Works......!!!!

Contents

            ·  Introduction

     · Components

     · Working Principal of Components

     · Working Principal of circuit

    ·  Usage

Introduction

  POWER SUPPLY:

 A power supply is a device that supplies electric power to an electrical load. The term is most commonly applied to electric power converters that convert one form of electrical energy to another, though it may also refer to devices that convert another form of energy (mechanical, chemical, solar) to electrical energy. A regulated power supply is one that controls the output voltage or current to a specific value; the controlled value is held nearly constant despite variations in either load current or the voltage supplied by the power supply's energy source.

   12 VOLT DC VARIABLE POWER SUPPLY:

 A 12 volt power supply is a circuit containing several components, get an input of 220v Alternating current                             and as an output it offers 12v direct voltage/current. It could be of any shape but the mainframe circuitry should be same for every 12 volt DC power supply.

The output given to load can be varied between 0 to 12 volt using a variable resistor which converts our power supply into a variable power supply.

Components

  Components used in our power supply are listed below

1.     Transformer  of  12v & 1 amp step down

2.     Vero board

3.     Jumper  wires

4.     Switch

5.     1N4001 diodes  x  4

6.     Capacitor    1000µf , 25 v  ( polar )

7.     Capacitor    100nf (non-polar)  x  2

8.     Capacitor  1µf , 25-50v

9.     L 7812CV  voltage regulator

1  .   Light emitting diode

Working Principal of Components

   TRANSFORMER:

 Electrical Power Transformer is a static device which transforms electrical energy from one circuit to another without any direct electrical connection and with the help of mutual induction between to windings. It transforms power from one circuit to another without changing its frequency but may be in different voltage level.
The working principle of transformer is very simple. It depends upon Faraday's laws of Electromagnetic Induction. Actually mutual induction between two or more winding is responsible for transformation action in an electrical transformer.According to these Faraday's laws,

Rate of change of flux linkage with respect to time is directly proportional to the induced EMF in a conductor or coil".

   VERO BOARD, SWITCH, JUMPER WIRES:

 Vero board is a sheet containing series of wholes which helps to place components efficiently and easily

 Switch is used to control the input, whenever switch is turned off it makes circuit open and currant will not flow through the circuit, and jumper wires are used to connect the components

   
        DIODES:

 In electronics, a diode is a two-terminal electronic component with an asymmetric transfer characteristic, with low (ideally zero) resistance to current flow in one direction, The essential feature of a diode bridge is that the polarity of the output is the same regardless of the polarity at the input. It’s most common application, for conversion of an alternating current (AC) input into a direct current (DC) output, using four diodes it is known as a bridge rectifier.

All diodes have a voltage drop which is commonly 0.7 or 0.3 volts.
  

   CAPACITOR:

  A capacitor is an electronic device which stores electric change.

Here we used four capacitors every capacitor has its own function

      Capacitor of 1000µf, 25 volts

This capacitor is used to smooth the input current cycle which is rectified by the diodes. When the positive cycle is on then capacitor gets charged and when the –ve cycle is on then it get discharge and use the stored charge to make the current wave smooth.

2     Capacitors of 100nf :

When a load is placed in the circuit the capacitor of 1000µf get discharged soon and cannot make that wave smooth completely as well as the diodes take some time to in switching (blocking and allowing) which allow some to flow in back side as shown so these capacitor make wave moor smoother as well as block that back flow of current which is known as NOISE for this property these capacitors are known as blocking capacitors. 

   VOLTAGE REGULATOR:

 A voltage regulator regulate the voltage at cretin value (here it is 12 volts), if the input voltage is greater than that value the regulator will block that extra voltage and if the value is less then that cetin value then it will allow all the voltage whatever it is to flow through.

Working principle of circuitry

A 12 volt step down transformer is placed at the ac input terminal to step the voltage down on 12 volt AC then a diode bridge is plac ed which is  an arrangement of four (or more) diodes in a bridge circuit configuration that a bridge rectifier provides full-wave rectification from AC input.A capacitor is used then to smooth the output of rectifier after that some blocking capacitors are also used to block the Noise in the circuit.

When the capacitor is connected directly to the bridge, as shown, current flows in only a small portion of each cycle, current will flow through the bridge only during the time when the input voltage is greater than the capacitor voltage. For example, if the load draws an average current of n Amps, and the diodes conduct for 10% of the time, the average diode current during conduction must be 10n Amps. This non-sinusoidal current leads to harmonic distortion and a poor power factor in the AC supply. Another non polar capacitor is used to overcome this problem which absorb most of the distortion and make our supply more efficient. A variable resistor is used at the end in parallel which help us to control the output voltage from 0 to 12 volts. At the end Led is placed to show that current is flowing through our circuit correctly.

Usage

This power supply can be used to operate any instrument which works on 0 to 12 volts such as mobile chargers and computers and etc.

We have to set the output first at a desired value using a variable resistor’s nob.

For example to charge a mobile phone battery we need a 5 volt input so we will set our output by rotating that nob which increase the resistance and decrease the output voltage, we will have to set that at 5 volts then connect the output terminals to the terminals of battery and our charging of that battery will start. 

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