When a positive signal is applied GTO starts conducting before initiation of conduction anode current is zero and anode to cathode voltage Vak is the peak reverse voltage. When conduction starts anode current rises from to full value and the anode to cathode voltage Vak becomes very small when a negative gate signal is applied the anode current becomes zero and the Vak rises to peak revise voltage. The total turn OFF time can be divided in three distinct times storage time fall time and tail time the switching characteristic of a FTO is shown in figure.
As soon as negative gate signal is applied turn OFF process starts immediately. The time clasping between application of negative gate current till this current reaches its negative peak value known as storage time. During this period the excess charges are removed by the negative gate current and GTO gets ready to turn OFF. During fall time tf the anode current decrease rapidly and anode to cathode voltage rises. This time tf in most GTO is about at the end to tf the current falls slowly to zero value during tail time tf. At the end to the tail time the anode current Ia becomes zero and Vak becomes equal to peak reverse voltage.
There are many advantages and disadvantage of GTO over thyristor some advantages of GTO are as follows:
a.Commutation circuit is not needed
b.Fast switching speed
c.More di / dt at turn ON
d.Higher efficiency because losses in commutations circuit is eliminated
e.Circuits using GTO are compact
f.Lesser acoustical and electromagnetic noise due to elimination of choke of commutation