Docstoc

rectifier (PowerPoint)

Document Sample
rectifier (PowerPoint) Powered By Docstoc
					HALF WAVE RECTIFIER

               Presented by:-
               Aman (ECE/08/102)
               Ashish (ECE/08/107)
               Pradeep (ECE/08/131)
               Reetu (ECE/08/142)
What is Rectifier?
   A rectifier is an electrical device that converts alternating current
   (AC) to direct current (DC), a process known as rectification.
   Rectifiers have many uses including as components of power
   supplies and as detectors of radio signals. Rectifiers may be
   made of solid state diodes, vacuum tube diodes, mercury arc
   valves, and other components
   When only one diode is used to rectify AC (by blocking the
   negative or positive portion of the waveform), the difference
   between the term diode and the term rectifier is merely one of
   usage, i.e., the term rectifier describes a diode that is being
   used to convert AC to DC. Almost all rectifiers comprise a
   number of diodes in a specific arrangement for more
   efficiently converting AC to DC than is possible with only one
   diode
Half-wave Rectifier




     Rectifier is a device that can convert ac
      voltage into dc voltage.
MATERIAL REQUIRED

    Transformer :
     It is device which is used to increase or decrease the
     alternating current and alternating voltage. For the
     rectifier, it may be step down or step up.
    Junction Diode :
     It is made up of p-type and n-type semiconductor
     which conducts when the p terminal of diode to
     connect to positive terminal of battery and n region is
     connected to negative terminal of battery i.e. during
     forward biased and does not conduct during reverse
     biased.
Half wave rectification
    In half wave rectification, either the positive or
     negative half of the AC wave is passed, while
     the other half is blocked. Because only one
     half of the input waveform reaches the output,
     it is very inefficient if used for power transfer.
     Half-wave rectification can be achieved with a
     single diode in a one-phase supply, or with
     three diodes in a three-phase supply.
    The process of removing one half the input
     signal to establish a dc level is aptly called half
     wave rectification.
Transformer-coupled Input Voltage

    Transformer is used to
     couple the ac input
     voltage from the source
     to the rectifier.
    Advantages of using
     transformer:
    Adjust the source         n  N sec N pri
     voltage to be stepped
     up or stepped down        V(sec)  nV( pri )
    Prevent shock hazard in   V p ( out ) V p (sec)0.7V
     the secondary circuit
                               PIV V p (sec)
    Operation of half wave rectifier
   During the positive half cycle of the input voltage the polarity of
    the voltage across the secondary forward biases the diode. As a
    result a current IL flows through the load resistor, RL. The forward
    biased diode offers a very low resistance and hence the voltage
    drop across it is very small. Thus the voltage appearing across
    the load is practically the same as the input voltage at every
    instant.
   During the negative half cycle of the input voltage the polarity of
    the secondary voltage gets reversed. As a result, the diode is
    reverse biased. Practically no current flows through the circuit
    and almost no voltage is developed across the resistor. All input
    voltage appears across the diode itself.
Operation of half-wave rectifier
(ideal diode)
Average Value of Output Voltage




                                 Vp
                    V( avg ) 
                                 
     Vavg Approximately 31.8% for a half wave
      rectified voltage.
Operation of half-wave rectifier
(practical diode)




                   V p ( out )  V p ( in )  0.7V

     The input voltage must overcome the barrier potential
      (0.7V) before the diodes becomes forward-biased
     Result: A half-wave output with a peak value that is
      0.7V less than the peak value of the input
Power supply specification

  The required output dc voltage.
  The average and peak currents in the
   diode.
  The peak inverse value (PIV) of each
   diode.
  The regulation.
  The ripple factor.
Analysis of Half-Wave Rectifier

  Peak  inverse.
  Average & peak currents in the diode.
  DC output voltage.
  RMS current & voltage.
  Rectification efficiency.
  Ripple factor
  Regulation
Peak loss
     An aspect of most rectification is a loss from the peak
      input voltage to the peak output voltage, caused by the
      built-in voltage drop across the diodes (around 0.7 V
      for ordinary silicon p-n-junction diodes and 0.3 V for
      Schottky diodes). Half-wave rectification and full-wave
      rectification using two separate secondaries will have
      a peak voltage loss of one diode drop. Bridge
      rectification will have a loss of two diode drops. This
      may represent significant power loss in very low
      voltage supplies. In addition, the diodes will not
      conduct below this voltage, so the circuit is only
      passing current through for a portion of each half-
      cycle, causing short segments of zero voltage to
      appear between each "hump".
Peak Inverse Voltage (PIV)




                        PIV  V p (in )

    PIV – maximum value of reverse voltage which occurs
     at the peak of the input cycle when the diode is
     reverse-biased
    PIV is equals to the peak value of the input voltage
Equation Laws And Formulae Used

    Efficiency
Ripple Factor

    Ripple factor
Transformer Utilization Factor
   Form Factor      Peak Factor
Disadvantage of Half-Wave Rectifier


    Half wave rectification involves a lot of wastage of
     energy and hence it is not preferred.
    A small current flows during reverse bias due to
     minority charge carriers. As the output
     across (RL) is negligible.
    The resulting d.c. voltage is not steady enough for
     some purpose. The following device is used when
     a very steady d.c. voltage is required.
FINAL DESIGN
   The simplest rectifier circuit is nothing
    more than a diode connected in series
    with the ac input, as shown to the right.
    Since a diode passes current in only one
    direction, only half of the incoming ac
    wave will reach the rectifier output. Thus,
    this is a basic half-wave rectifier.
In half wave rectification, either the positive or negative half of the
AC wave is passed, while the other half is blocked. Because only
one half of the input waveform reaches the output, it is very
inefficient if used for power transfer. Half-wave rectification can be
achieved with a single diode in a one-phase supply, or with three
diodes in a three-phase supply.
Waveform
   Result: - The output waveform may be
    observed in the waveform viewer

				
DOCUMENT INFO
Shared By:
Stats:
views:551
posted:5/8/2010
language:English
pages:24