Difference between SCR and DIAC

The word thyristor denotes a family of semiconductor devices used for power control in dc and AC system. A thyristor is also called silicon control rectifier (SCR) is basically four semiconductor rectifier. While in DIAC stands for is bidirectional or full wave switch that can be turned on in both forward and reverse polarities. The name of word DIAC comes for the words DIode AC switch. Here this page gives information about the comparison between ASCR and DIAC to better understand this topic.

SCR:
  • SCR stands for silicon control rectifier.
  • SCR is a four layers PNPN device with three terminals namely anode, cathode, and gate.
  • SCR is a high power device.
  • SCR is a three terminal device.
  • SCR break over voltage can be controlled by adjusting the gate current.
  • SCR breakdown voltage is plus or minus 26 V. The maximum anode current is 25 mA.
  • SCR is a unidirectional switch. It conducts current only in one direction. So it can control only for DC power or it can control forward biased half cycle of AC input in the load.
  • SCR can only control either the positive or negative half cycle of AC input.
  • SCR is used in application like a dimmer, control light, fan, etc.
DIAC:
  • DIAC stands for diode alternating current.
  • A diode is basically a two terminal device and it is a parallel inverse combination of semiconductor layers and it permits triggering in either direction.
  • DIAC is a low power device.
  • DIAC is a two terminal device.
  • DIAC break over voltage cannot be controlled.
  • The forward break over voltage is 40 V. The maximum anode current is 100 A.
  • DIAC can be switched from its off state to ON state for either polarity of the applied voltage.
  • DIAC can be made in PNP or NPN structure form. 
  • DIAC we used as triggering device for the TRIAC.

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