Title : Rectification

Apparatus :

     Science Workshop Interface 750                                          1

        Voltage sensor  ( PASCO CI-6503 )                                        3

        Low voltage power supply                                                     1

                ( with westminster electromagnetic kit )

        light bulb 12 V                                                                      1

        smoothing unit                                                                       1

                -                                                              2

               -  1000 - turn coil mounted on a closed soft iron core     1

　

Objective :

1.    Study conversion of  a.c. to d.c.  by a rectifier

2.    Study simplest smoothing circuit consisting of a large capacitor

3.    Study smoothing circuit consisting of capacitor-input filter

                - a choke L ( i.e. an iron-core inductor ) and a large capacitor

　

Theory :

Half-wave rectification

click to play movie

In the first half-cycle, the diode is in forward biased and a pulse of current flows round the circuit.

In the next half-cycle, the diode is in reverse biased and no current flows round the circuit.. 

Full-wave rectification

(i)    Centre-tap full-wave redtifier

which is equivalent to the following circuit  

   click to play movie

 

In the first half-cycle, diode D1 is forward biased, giving a current pulse in the circuit through the resistor. During this cycle, diode D2 does not conduct electric current.

In the next half-cycle, diode D2 is forward biased, giving a current pulse in the circuit through the resistor. During this cycle, diode D1 does not conduct electric current.

The current through the resistor is in the same direction during both half-cycles.

(i)    Bridge full-wave rectifier

click to play movie

In the first half cycle, diodes D1 and D2 are forward biased, giving a current pulse in the circuit through R. During this cycle, diodes D3 and D4 do not conduct electric current.

In the next half-cycle, diodes D3 and D4 are forward biased, giving a current pulse in the circuit through R. During this cycle, diodes D1 and D2 do not conduct electric current.

The current through the resistor is in the same direction during both half-cycles.

Smoothing Circuits

   (i)    Reservoir capacitor

          click to play movie     

  (ii)    Capacitor-input filter

             

            The above circuit is equivalent to the following circuit 　

          click to play movie

Procedure :

Hardware setup :

1.  Connect the Interface to the Computer, turn on  the interface, and turn on the  

     computer.

2. Connect the Voltage Sensors to the interface

3. Use the Voltage Sensors to measure the voltage across the resistor, capacitor and

    inductor

Software setup :

1.  Open Science Workshop

2.  Click Sampling Option 

3.  Select Periodic Samples : 4000 Hz and Stop Condition :  Sample Time  = 0.06 

     seconds

4.  Click Record button

Data Recording :

 Click the Record (REC) button to begin recording data.

Data sampling would stop automatically.

Data Analysis :

1.    Study conversion of  a.c. to d.c.  by a rectifier

2.    Study simplest smoothing circuit consisting of a large capacitor

3.    Study smoothing circuit consisting of capacitor-input filter

                - a choke L ( i.e. an iron-core inductor ) and a large capacitor

　

Discussion :

1.  Suggest a reason why a large capacitor is used in the simplest 

     smoothing circuit.

2.  What is the difference between centre-tap full wave rectifier and

      bridge full wave rectifier ?