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Sunday, 2 February 2020

What is Rectifier? Need and Types of Rectifier

Rectifiers


Rectifier is a device that converts Ac quantity into Dc quantity.


Circuit diagram of Rectifier
Circuit diagram of Rectifier 

Need of Rectifiers-

  • Almost all electronic devices such as diode, transistor, IC's, electronic circuits, electronic systems requires dc voltage for their proper operation.
  • This dc voltage can be supplied from dry cell and batteries. But these are consumable and also not economical for continues use.
  • The rectifier an electronic device have a property to convert ac quantity to dc quantity.
  • So rectifier can be used as a substitute foe the source of electric voltage.

Types of Rectifier-

1. Half wave rectifier 
2. Full wave rectifier
                  a) Center tapped full full wave rectifier
                  b) Full wave bridge rectifier

1. Half Wave Rectifier
  • Half wave rectifier will generate the waveform that will have average value of particular use in the ac to dc conversion process.
  • In positive half cycle diode is in forward biased that is turn ON the diode with the polarity.
  • Where it is fairly observe that the output signal is in exact replica of the applied signal.
  • In negative half cycle diode is in reverse biased that is turn OFF or open circuit with the polarity and the negative half cycle is removed.
  • The process of removing -ve half cycle to establish a dc level is called half wave rectification.
  • By applying ac input to a half wave rectifier, it allows +ve half cycle only and quench the -ve half cycle to the dc signal.
Advantages 
  • Simple in construction. 
  • Small in size. 
  • Requires less no of components for construction.
  • It is cheap.
Disadvantages 
  • It has excessive ripple factor.
  • Low rectifier efficiency.
  • Low transformer utilization factor.
  • It produces low output dc voltage and current.
  • Requires filter components of higher value.
Applications 
  • Used as eliminator.
  • Used in low cost power supplies.
  • Suitable for battery charger circuit.

Important terms- 

1. Peak Inverse Voltage (PIV)
Peak inverse voltage of diode is defined as the maximum voltage at which the junction diode must withstand without its damage during the negative half cycle of ac input.

2. Ripple
The ac components present in a rectifier output is called ripple.

3. Ripple Factor
The rate of change in rms value of ac components with respect to the dc component in the rectifier output is called as ripple factor.

4. Rectifier Efficiency
The rate of change in output power delivered to the load with respect to applied input ac power is called as rectifier efficiency.

5. Transformer Utilization Factor
The ratio of dc power delivered to load to the ac rating of transformer secondary called transformer utilization factor.

6. Ripple Frequency
The no of ripple pulses present in the rectifier output per second is called ripple frequency.


2.Full Wave Bridge Rectifier


  • The disadvantages of half wave rectifier is overcome by full wave rectifier.
  • A full wave rectifier is a circuit which allows a unidirectional current flow through the load during the entire period of ac input.      
a. Center tapped full wave rectifier

Advantages 
  • DC output voltage and load current is twice. 
  • Ripple factor is much less.
  • Rectifire efficiency is twice 
  • It has better TUF.
  • No possibility of core saturation of transformer secondary.    
Disadvantages 
  • Output dc voltage is half of the secondary voltage.
  • Requires high reverse voltage breakdown diode because PIV is double.
  • Diodes are costly due to higher voltage rating.
  • It is expensive to manufacture the center tapped transformer.      
Applications                 
  • Used in power supplies.
  • Used in high current power supplies.
  • Used in battery charger.
  • Used in power supplies for various electronic circuits.
b. Full wave bridge rectifier

Advantages 
  • Used in applications allowing floating output terminals that is no output terminals is grounded.
  • Permanent use of center tapped transformer is eliminated.
  • No possibility of core saturation of transformer secondary winding.
  • PIV reduces to 1/2 that of the center tap rectifier.
  • Output is twice that of the center tap circuit for the some secondary voltage.
  • TUF is large 0.812
  • Rectifier efficiency is high 81.2%
Disadvantages
  • It requires four semiconductor diodes.
  • Two diodes conducts in series at a time on alternate half cycle. This creates a problem when low dc voltage are required. This leads to poor voltage regulation.
Applications
  • Used in high current power supplies.
  • Used in laboratory dc power supplies.
  • Used in battery chargers.
  • Used in dc power supplies used for various electronic circuits.

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