What is half wave rectifier?,Diode,Types of Rectifiers,Working Principle of Rectifier.Efficiency of Half wave rectifier.

Diode
               Diode is a semiconductor device having two terminals typically allowing the flow of current in one direction only.One important application of diode is in rectifier circuits.Rectifiers converts cheaply available mains(ac) power supply voltage in a dc power supply.Electronic circuits such as television,receivers,radio and many more need a dc power supply.
Rectifiers
                We have main three types of rectifier circuits.
  • Half wave rectifier circuits.
  • Full wave bridge rectifier circuit.
  • Full wave rectifier with center tapped transformer.
Half Wave rectified
      fig.
     
                   A basic half wave rectifier circuit is show in the diagram in which
                  
                           Vin=input voltage
                            Vo=output voltage
                            Id=IL=load current
                            main voltage=220v ac
                            T= transformer
                             D= diode
                              Rl= load resistance
  • Main ac voltage in step down and applied to the rectifier circuit which is Vin.During the positive half cycle the diode will be forward biased and will conduct forward current through the load resistor Rl.Due to this an output voltage Vo will appear across the load as shown in the fig.(c) The solid wave form represents that an ideal diode is used and the dotted waveform represents that the diode is a practical diode in which Vd=0.7volt and rd=0ohm .The diode current Id will be equal to the load current IL.
  • During the negative half cycle the upper end of secondary winding will be negative with respect to its lower end and therefore the diode will be reverse-biased and will turn off (open circuit).This means no current can flow through the diode and the load and no voltage will develop across Rl.This implies that the negative half cycles will appear across the diode.This is represented in the wave form of fig.(d).
  • The point should be noted that the output voltage (Vo) is not a steady-state dc voltage but a pulsating one. that is a dc value plus an ac component (usually called as ripple).If a dc meter is used to measure Vo the meter will read only the dc or average component of Vo.
  • Maximum magnitude of the output(Vo) will be Vmax for an ideal diode and Vmax-0.7 V for a silicon diode.
  • Maximum reverse voltage across the diode (during negative half cycle) will also be Vmax and the peak inverse voltage (PIV) rating of the diode should be better than Vmax or the maximum magnitude of Vin.
  • The name half wave rectifier originates from the fact that only half cycles (in this case positive) are delivered to the load it in shown in fig.c  .The negative half cycles are suppressed and they never reach the load and appear across the diode,as shown in the fig.d .
Efficiency of HW- Rectifier
       
                      Efficiency of HW-rectifier is defined as the ratio of the output dc power delivered to the load resistor Rl and the ac power drawn from the source that is the secondary winding of the transformer in mathematical form

                               η of HW= Pdc/ Pac

                             Pdc=VdcIdc
                               
                              Pac= VrmsIrms=(Vrms)2/Rl
                            
                              Pac=(Vmax/sqr2)2/Rl   =   (Vmax)2/2Rl

                               Pac=(Vorms)2/Rl

                                Pac= (Vmax/2)2/Rl  =  (Vmax)2/4Rl

                                Pdc=(Vmax/π)(Vmax/π)(1/Rl)  =  (Vmax)2/(π2Rl)

                                
                                  η of HW= (Vmax)2/(π2Rl) * 4Rl/(Vmax)2 =4/π2 = 40.6%
               
                      This shows that out of 100% power drawn from the secondary winding of the transformer only 40.6% power is usefully delivered to the load and the rest of power is wasted in the remaining circuit.This indicates an inefficient dc power supply system.efficiency of the half wave rectifier can be improved by using filters which can smooth out the harmonics and remove or reduce the pulsations (ripples) from the out put voltages.This will give a better dc power supply which is usually a must for most of the electronic circuits.The efficiency of the full wave rectifier is better than that of HW rectifier. 
                              
                             
                                      

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