Critical Rate of Rise of Voltage

It  depends on  the junction temperature higher  the junction  temperature lower  the critical rate of  rise of  voltage. It is also known  as static dv/ dt. The  switching  from the off state  to the   on state with  gate  open  is known  as forward dv/ dt rating.  A high  value of dv/dt  at which  a thyristor just gets  tumed on is  called  critical rate of  rise of voltage. If the applied  rate of  rise of  voltage is more than its  critical  value thyristor gets  tumed on. This  false triggering is because  of the capacitance passed by the large  of junctions J2.  When the  rate  of rise of  the applied  voltage  dv/ dt  is very  large the capacitive charging current Ddv/ dt may  becomes  large  enough  to trigger the device. This is not  likely  to damage the device but an  unintended triggering may  lead to either high  di/ dt  through  the SCR  or large  shortest circuit  current which  may lead  to the failure of  the device.