Half Wave Rectifier and Full wave Rectifier

Half Wave Rectifier :-

• The half wave rectifier conducts current only during the positive 

   half cycles of the input supply voltage.

• The negative half cycles  of the a.c. supply are suppressed. So no 

current is conducted and hence no voltage appears across the load. 

So current always flows in one direction (i.e. d.c. ) through the 

load.

• The a.c. supply is applied in series with the diode D and load 

  resistance RL.

• The a.c. supply is normally applied through a transformer. It 

gives two advantages. First it allows us to step up or step down the 

a.c. input voltage as required. Secondly, the transformer isolates 

the rectifier circuit from power line and thus reduces the risk of 

electric shock.

Operation:-

• During the positive half cycles of input supply voltage, end A 

becomes positive with respect to end B.

• This makes the diode D forward biased and hence it conducts 

current.

• During negative half cycles, end A becomes negative with respect 

to end B. So the diode D is reverse biased and hence conducts no 

current.

• So current flows through the diode only during the positive half 

cycles of the input a.c. voltage.

• Hence current flows through the load RL always in the 

same direction and d.c. output is obtained across RL

• In half wave rectifier , output across the load is pulsating. So a 

filter circuit is used to smoothen the  output.

Full wave Rectifier :-

• In full wave rectifier , current flows through the load in the same 

direction ( i.e. d.c.) for both the half cycles of input a.c. supply 

voltage. There are two types of circuits commonly used for full-

wave rectifications.

• Center-tap full wave rectifier.

• Full wave bridge rectifier.

                            

                                        Fig(3):-   Full wave Rectifier

                 Fig(4):- Full wave Rectifier

• Fig(3) shows the circuit diagram of a Centre-tap full wave 

rectifier and  Fig(4) shows the input and output waveform of a 

centre-tap full wave rectifier .

• The circuits uses two diodes D1 and D2. A centre-tap 

secondary winding AB is connected with the two diodes such 

that each diode uses one half-cycle of input a.c. voltage. That 

means diode D1 utilises the the upper half of secondary winding 

for rectification and diode D2  uses the lower half.

Operation :-

• During the positive half cycle of secondary voltage, the end A 

of the secondary winding  becomes positive and end B negative.

• So diode  D1 is forward biased and diode D2 is reverse biased. 

  Hence, diode D1 conducts and diode D2 does not.

• The current flows through diode D1, load resistance RL and the 

upper half of the secondary winding OA. This is shown by 

the red colored arrows.

• During the negative half cycle of secondary voltage, the end A 

of the secondary winding  becomes negative and end B positive.

• So diode D2 is forward biased and  D1 is reverse biased. Hence 

   D2 conducts while D1 does not.

• The conventional current flows through diode D2 , load 

resistance RL and the lower half of thr secondary winding OB as 

shown by the green colored arrows.

• As we can see that current in the load RL  flows in the same 

direction for both the half cycles of input supply voltage. So d.c. is  

obtained across RL.

Full Wave Bridge Rectifier :-

• Fig(5) shows the circuit connection of a full wave bridge rectifier 

and Fig(6) shows the input and output waveform of  full-wave 

bridge rectifier.

• The full wave  bridge rectifier circuit  contains four diodes D1 , 

D2,D3 and D4, connected to form a bridge as shown in Fig(5).

• The a.c. supply is applied to the diagonally opposite ends A and 

B of the bridge through the transformer.

• The load resistance RL is connected between other two ends of 

the bridge i.e. P and Q.

Operation:-

• During the positive half cycle of secondary voltage, the end A of 

 the secondary winding becomes positive and end B negative.

• This makes diodes D1 and D2 forward biased while D3 and 

 D4 are reverse biased. Hence  only diodes  D1 and D2 conducts.

• The conventional current flows through load RL is shown by 

  the red colored arrows .

• During the negative half cycle of secondary voltage, end A 

  becomes negative and end B positive.

• This makes diodes D3 and D4and forward biased  and  diodes 

D1 and D2 are reverse biased. Hence only diodes D3  and 

D4  conducts.

• The conventional current flow through load RLis shown by 

  the green colored arrows.

• It can be seen that the current flows through the load RL in the 

same direction for both the half-cycles. Hence d.c. output is 

obtained across load RL.

                                        Full Wave Bridge Rectifier