Experiment: Converting AC to DC (Rectifiers)

 

 

Objectives:

• To investigate the function of a diode
• To convert AC into DC
• To compare different types of rectifiers
• To reduce DC-ripple

 

Material needed:

            1 AC-Power supply (5V- 25V, depending on type of diode)

            5 diodes (e.g. 1N4001, 1N4004)

            1 electrolyte capacitor C₁ (small capacity e.g. 22uF/40V)

            1 electrolyte capacitor C₂ (big capacity e.g. 1000uF/40V)

            2 light bulbs (voltage depending on power supply voltage used)

1 bread board

            1 oscilloscope (2 channels)

            cables

 

Experiment 1: Half-Wave-Rectifier

 

1. Set up circuit 1
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
2. Use oscilloscope to display U_AC (channel 1) and U_L (channel2)
3. Bypass diode with cable 1
4. Adjust AC-Power Supply to the chosen voltage
5. Switch on AC-Power Supply
6. Graph U_L for the protocol (U_L=U_L11)
7. Remove cable 1
8. Graph U_L for the protocol (U_L=U_L12)
9. Add the smaller capacitor C₁ to the circuit (parallel to the lamp)
10. Graph U_L for the protocol (U_L=U_L1C1)
11. Remove capacitor
12. Add the larger capacitor C₂ to the circuit (parallel to the lamp)
13. Graph U_L for the protocol (U_L=U_L1C2)
14. Switch off power supply
15. Disconnect oscilloscope
16. Analyze the resulted graphs

 

Experiment 2: Bridge-Rectifier (Full-Wave-Rectifier)

 

1. Set up circuit 2
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
2. Use oscilloscope to display U_L
   
   

ATTENTION !!! DO NOT MEASSURE U_AC AND U_L WITH THE OSCILLOSCOPE SIMUNTANOUISLY !!!

Different ground potentials are connected. This can cause damage to the oscilloscope or the electronic circuits.

 

3. Adjust AC-Power Supply to the chosen voltage
4. Switch on AC-Power Supply
5. Graph U_L for the protocol (U_L=U_L21)
6. Add the smaller capacitor C₁ to the circuit (parallel to the lamp)
7. Graph U_L for the protocol (U_L=U_L2C1)
8. Remove capacitor
9. Add the larger capacitor C₂ to the circuit (parallel to the lamp)
10. Graph U_L for the protocol (U_L=U_L2C2)
11. Switch off AC-Power Supply
12. Analyze the resulted graphs
    
    

 

Explanation:

Setup of the circuits for both types of rectifiers: =>

 

 

The following diagrams show photos taken from the screen of a digital oscilloscope. Ground level is indicated by the marks “1” and “2”.

 

 

 

Experiment 1: Half-Wave-Rectifier:

 

U_L11: U_L11 = U_AC, AC-50Hz Sine Wave, diode bypassed

 

 

Voltage without capacitor (U_L12):

 

U_AC

U_L12

 

Current in positive direction (anode => cathode, positive half-wave) can pass the diode.

Current in negative direction (negative half-wave) is not able to pass. => only the positive half-wave appears.

 

 

Voltage with small capacitor C₁ (U_L1C1 ):

 

U_AC

U_L1C1

 

Capacitor C₁ is charged by the increasing voltage of the positive half-wave and discharged during the decrease of the half-wave and the zero-voltage period. Due to the small capacitance voltage U_L1C1 has high ripple.

 

 

 

 

 

Voltage with large capacitor C₂ (U_L1C2):

 

U_AC

U_L1C2

 

Due to the larger capacitance C₂ the voltage U_L1C2 is not dropping so low

=> ripple is low.

 

 

 

 

Experiment 2: Bridge-Rectifier (Full-Wave-Rectifier):

 

ATTENTION !!! DO NOT MEASSURE U_AC AND U_L WITH THE OSCILLOSCOPE SIMUNTANOUISLY !!!  Here U_AC is taken from a saved reference channel !!

Voltage without capacitor (U_L21):

 

U_AC

U_L21

 

Positive and negative current can find paths over the diode network. Therefore the negative half-wave is clapped to positive voltage.

 

 

 

Voltage with small capacitor C₁ (U_L2C1 ):

 

U_AC

U_L2C1

 

Capacitor C₁ is charged by the increasing voltage and discharged during the decreasing voltage. Because of the smaller decreasing period the voltage U_L2C1 does not drop so much.

 

 

 

 

 

 

 

 

 

 

 

Voltage with large capacitor C₂ (U_L2C2):

 

U_AC

U_L2C2

 

 Due to the larger capacitance C₂ the voltage is not dropping so low

=> ripple is low.

           

 

 

 

 

 

 

 

 

 

 

 

 

Conclusion:

 

The two methods converting AC to DC are shown =>

 

Top to bottom:

·        Supplied AC-Voltage

·        Half-Wave-Rectifier

·        Bridge-rectifier

 

The ripple can be decreased by using capacitors.

 

 

 

 

 

 

           

 

 

This experiment was designed and presented at

CERN, HST-2002 programme by:

Dipl.-Ing. Dr. Gerd Vogt

Hoehere Lehranstalt fuer Umwelt und Wirtschaft

3683 Yspertal, Austria

http://www.hlaysper.ac.at

gvogt@hlaysper.ac.at