5 March 2018

Compare SCR and Asymmetrical SCR ( ASCR )

SCR

  • It has thousand of volts reverse blocking capacity. However it may not requires in some applications particular in the inverter
  • The flywheel diode is connected in anti parallel with load in order to conduct inductive load. 
  • The peak repetitive voltage rating of the SCR is higher than the ASCR. 
  • The on state voltage drop and turn off time of the SCR is higher than the ASCR.

Asymmetrical SCR

  • The reverse blocking capacity of the ASCR is very low. It is in the order of 20  to 30 V. 
  • The ASCR is useful where very low reverse blocking capacity requires. 
  • The forward blocking capacity of the ASCR is very high typically 400 to 2000 V. The forward and reverse blocking capacity of the ASCR are not equal. 
  • There is additional N2+ layer added in the ASCR therefore N2   become narrow. The N2+ layer is acts as Electrical field stopper. 
  • The P2N2+ junction avalanches at very low voltage therefore the ASCR does any usable peak repetitive voltage rating ( VRRM ).  
  • The ASCR has faster turn off time and reduction in ON state voltage is achieved by sacrificing reverse voltage blocking capacity. 
  • If the gold doping is same as that of conventional SCR, the on state voltage drop is reduced but turn off time is unaltered. 
  • It should be noted that the on state voltage drop and turn off time of the ASCR is adjusted by suitable doping level of N2 .
compare scr and asymmetrical scr

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