26/04/2017

Heat Sink

  • The function of the heat sink is to absorb heat of the semiconductor device and dissipates it to surrounding medium by thermal conductivity. 
  • It transfers heat from high temperature to low temperature. The heat sink plays important role for cooling of semiconductor device.

20/04/2017

Selenium Diode

Metal Oxide Varistor ( MOV )

Metal oxide Varistor (MOV)
  • The MOV is a non linear resistor.  
  • There are two metal particles oxide layers are separated by insulation. When voltage across MOV increases beyond its specific value, the

14/04/2017

Snubber Circuit

  • The SCR may be turned on due to transient or high dv/dt voltage across it in spite of switch S is kept open. 
  • The SCR may damage due to this type of surge voltage. 

13/04/2017

Over Voltage Protection of Semiconductor

  • When the SCR is turned on , its maximum voltage rating must be less than the specific rating of the SCR
  • There are following main reasons for generation of over voltage or transient voltage.

10/04/2017

Over Current Protection of Semiconductor by Fuse

  • The fault current flows through power converter due to short circuit, surge current or over load condition. 
  • The semi conductor device may damage due to increase of temperature due to fault current.  

Current - Time Characteristic of Fuse

Current – Time Characteristics
  • The fast acting fuse is used to protect semi conductor device. 
  • The fuse is connected in series with semi conductor device and it open when the current exceeds its rated value. 

09/04/2017

Function of Freewheeling Diode

  • The diode is connected across load in the controlled or uncontrolled converter circuit. This diode is called as freewheeling diode or flywheel diode

08/04/2017

Effect of Transformer Winding Reactance on Performance of Three Phase Uncontrolled Rectifier

 Effect of Transformer Winding Reactance
  • The effect of transformer winding reactance on the performance of output voltage / current is explained here. 
  • The conduction of diode D1, D2 and D3 and resulting flow of current is shown in the figure A. 

07/04/2017

Working of Six Phase Half Wave Uncontrolled Rectifier


05/04/2017

Working of Three Phase Uncontrolled Full Wave Rectifier

  • The connection diagram for three phase full wave uncontrolled rectifier using Delta – star transformer is shown in the figure A. 
  • There are two diodes used for each phase and load is connected between common anode terminal and common cathode terminal of diodes. 

Working of Three Phase Half Wave Uncontrolled Rectifier

  • Figure A shows a three phase half wave uncontrolled rectifier circuit using delta – star transformer
  • The anode of the diode D1, D2 and D3 are connected to the secondary winding of the transformer with R phase, Y phase and B phase respectively. 

Comparison between Three Phase Uncontrolled Rectifiers

  • The single phase rectifiers are generally used for low power applications of electronic circuits. 
  • They are used for supplying DC loads up to 5 kW. However the single phase rectifier circuit have following advantages.

Class F Commutation ( Line commutation or AC commutation )

    • The class F commutation is also called as line or natural commutation because the SCR is turned off automatically during negative cycle of alternating supply. 
    • There are no commutating components used in this method therefore it is not called as forced commutation method.

    Class E Commutation ( External Pulse or Type E commutation )

    • The class E commutation is also called as external pulse commutation because the SCR is turned off by external source. 
    • The SCR is turned off by applying reverse voltage across it.
    • Figure A shows the external pulse commutation by using transistor.

    04/04/2017

    Class D Commutation ( Impulse or Auxiliary Commutation )

    • The class D commutation is also called as impulse commutation. 
    • The SCR T1 is main SCR whereas SCR T2 is auxiliary SCR. 
    • The auxiliary SCR T2 is used to turn off main SCR T1 therefore this method is also called as auxiliary commutation.

    02/04/2017

    Class C Commutation ( Voltage or Complementary or Type C Commutation )


    • The class C commutation is also called as voltage commutation because the SCR is turned off by applying reverse voltage across it.
    • The SCR T1 is main SCR which is connected in series with load. 
    • The commutating capacitor C is connected between anode terminal of SCR T1 and SCR T2. 

    01/04/2017

    Class B Commutation ( Self or Type B Commutation )

    • The commutating components L and C are connected in parallel with SCR T1 in the class B commutation. 
    • When SCR T1 is turned off, the charging of capacitor is done through path(+)Vdc – (+)C –C(-) – L – RL –Vdc(-).