Electrical Interview:TURN ON TIME OF SCR

Delay Time: Practically delay time depends on gate signal magnitude Ig. If Ig increase,initial conduction area increases due this rate of raise of anode current increases therefore Td delay time decreases and turn ON time decrease.                                                                                                                                                          

Raise Time: Raise time in the SCR depends on load parameters for example L is increases the di/dt of SCR decrease and raise time increase then turn ON time increase.                                                  

                 

 Spread Time: Spread time depends on the physical geometrical structure of the device.                                       

                 From above conclusion for inductive loads turn ON time is higher.                

Electrical Interview:THYRISTOR

                               Thyristor  is a semi controlled rectifier because when ever a positive voltage is applied at anode and negative voltage is applied at cathode,the thyristor goes in to forward blocking mode at this mode we can control the thyristor by using gate.                                                                                                   

                      

                            All power transistors and GTO are fully controlled rectifiers.                                                                                                                          but in the next case when ever a positive voltage is applied at cathode and negative voltage is applied at anode the thyristor goes in to reverse blocking mode,in this mode we can not apply the gate,otherwise the gate is applied the thyristor comes into thermal runaway,after some time the thyristor burned.Due to this thyristor is controlled only in one mode by using gate,according to this type of operation thyristor is called semi controlled rectifier.