POWER SUPPLY

          TRANSFORMER BASED 5 V DC SUPPLY

     COMPONENTS REQUIRED

1. step down transformer 0-12
2. 1N4007  DIODES 4 pieces
3. 1000uf 25 V electrolytic capacitor
4. 7805 voltage regulator
5. led
6. resistor 1k ohms
7. 100nf capacitor              

 TRANSFORMER

     To make power supply we require to step down the 220 voltage to 12 V which requires a step down 

     transformer . There are two basic types of transformer available in market , these are 

• Center tap transformer(12-0-12)
• bridge type transformer (0-12)

 we would use bridge type type. Also the transformers are available in different current ratings. we would use 12 V 750 ma transformer.  The diagram shown is a bridge type transformer 6 V 

DIODES

A diode is a device which allows unidirectional flow of current. the diode conducts in forward direction and acts as a closed switch. when  reverse biased , t acts as an open switch. 1N4007 diodes are the most general and widely available diodes in the market. the peak voltage that a diode can bear without getting damaged is 1000 V. the voltage drop across the 1N4007 diode is 0.7V .We would use 4 diodes in bridge configuration to generate rippled DC.

IN4007

ELECTROLYTIC CAPACITOR

Bridge configuration of  diode produces rippled DC ( DC with AC contents ). These fluctuations are not harmful for LED's or batteries but it could damage household appliances which are very sensitive to AC contents. So to suppress the ripples  we use 1000uf  25V electrolytic capacitor. 25V is chosen double of the input

 voltage. if any capacitor with voltage rating less than 25V is chosen then capacitor would blow.

                                                    ELECTROLYTIC CAPACITORS

VOLTAGE REGULATOR

Function of voltage regulator is to maintain the output voltage to fixed voltage  and The most commonly available voltage regulator is 78XX series. it is the positive voltage regulator series used available with large voltage range. XX tells us the output voltage of the the regulator when XX= 05 then the output voltage is 5V and the voltage regulator is known is 7805 having output voltage of 5V and of current 1A.
                                         

7805 VOLTAGE REGULATOR

LED 

LED or Light Emitting Diode are used as indicator to know whether the circuit is working correctly or not. LED is placed in series with the output of voltage regulator. a resistor is used to limit the current flowing through the LED. the voltage required to glow LED is 1.5V and current required is 20-70 ma.
                                                 

RESISTOR

resistor is used to oppose the large current and allow defined current to pass through the circuit. the value used in the circuit is 1k ohms and 1/4W  resistor is used.
                                           

resistors

CAPACITOR

ceramic capacitor of value 100nf is used at the output to suppress the sudden fluctuations when any load is connected.
                                         

WORKING

0-12 Transformer converts the 220 V ac into 12 V. the output is given to the bridge configuration of 1N4007 diode. diodes converts AC into rippled DC. the rippled DC is converted into pure DC by using filter. electrolytic capacitor is used as filter. the output level is maintained to constant level by voltage regulator. An LED is used as an indicator to check whether the circuit is working

                                             

      CAUTIONS  :

•    carefully connect the transformer with AC
•    The polarity of the electrolytic diode is very important. check the negative of electrolytic capacitor written on it
• check whether 7805 is heated too much  ,avoid direct touching  . the possible reasons may be short circuiting of pins of 7805 or large voltage applied to 7805