Switching characteristics

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  t_f the anode current decrease rapidly and anode to cathode voltage rises. This  time t_f in most GTO  is about at  the end to t_f the current falls  slowly to zero value during tail time  tf.  At  the end to the tail time  the anode current  I_a becomes  zero  and V_ak  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