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162 Power semiconductor devices and converter hardware issues

Having discussed the desired characteristics, we consider the various fully controlled
power semiconductors and their realistic characteristics in the next sections.

5.2.5 Gate-turn-off thyristor

This semiconductor device, as the name implies, is a hybrid device that behaves like
a thyristor. However, it has an added feature that the provided gate control allows
the designer to turn the device on and off if and when desired. It became commer-
cially available during the late 1980s although it was invented a long time ago (Van
Ligten et al., 1960). Recently it has undergone a number of improvements and in the
next few years may be able to replace the thyristor in the really high power area of
applications.
The GTO thyristor is a device similar to the conventional thyristor. However, it is not
just a latch-on device but also a latch-off one. The circuit symbol along with the layers are
shown in Figures 5.7(a) and (b). The equivalent circuit is depicted in Figure 5.7(c). Its
ideal and non-ideal i±v characteristics are plotted in Figures 5.7(d) and (e) respectively.

Fig. 5.7 GTO: (a) circuit symbol; (b) device structure; (c) equivalent circuit; (d) ideal i±v characteristics; and
(e) non-ideal i±v characteristics.