Gate turn-off switch (GTO) is, like an SCR, is a four layer, three junction semiconductor device with three external terminals, namely, the anode, the cathode and the gate, as illustrated in figure. The basic construction, schematic symbol of a GTO are shown is figures respectively. Although the graphic symbol is different from either the SCR or the SCS, the transistor equivalent is exactly the same and the characteristics are similar.
The main advantage of the GTO over the SCR or SCS is that it can be turned on or off by applying the proper pulse to the cathode gate (without the anode gate and associated circuitry required for the SCS). Because of its turn-off capability, there is an increase in the magnitude of the required gate current for triggering. For an SCR and GTO of similar maximum rms current ratings, the gate triggering current may be of the order of 30 uA and 20 m A respectively. The maximum rms current and dissipation ratings of GTOs manufactured today are limited to about 3 A and 20 W respectively.
Another distinct advantage of GTO is its improved switching characteristics. The turn-on time is similar to that of an SCR (typically 1 u s), but the turn-off time of about the same duration ( 1 u s) is much smaller than the typical turn-off time of an SCR (5 to 30 us). The fact that the turn-off time is similar to the turn-on time rather than considerably larger permits the use of this device in high speed applications.
The GTO gate input characteristics and turn-off circuits can be found in a comprehensive manual or specification/data sheet. Most of the SCR turn-off circuits can also be employed for GTOs. Some of the areas of application for the GTO include pulse generators, multivibrators, voltage regulators and counters.