Gate turn-off thyristors (GTO)

Production of GTOs commenced in the mid 1980s. A GTO is a thyristor that can be turned off by applying a current to the gate in the reverse direction to that required to turn it on.

GTOs are optimized for low conduction losses. The typical on-off switching frequency is in the range of 200 - 500 hertz for most applications. GTOs are, by nature, relatively slow switches.

Typical transition times from on to off state and vice versa are in a range of 10 - 30 microseconds. All GTOs require protective networks called "snubbers" for turn-on and turn-off. The turn-on snubber circuit, in essence an inductor, limits the rate of current rise. For turn-off, the GTO requires a device that limits the rate of voltage rise, in essence a capacitor.

All Hitachi Energy GTOs are press-pack devices. They are pressed with a relatively high force onto heat-sinks which also serve as electrical contacts to the power terminals.