Zeitschrift für Elektrotechnik und Elektronik

The Thyristor is etensively used in High Power Applications

Emily Wilson

A Gate Turn-Off thyristor (GTO) is a special type of thyristor, which is a high-power semiconductor device. It was invented by General Electric. GTOs, as opposed to normal thyristors, are fully controllable switches which can be turned on and off by their third lead, the gate lead. Although the thyristor is extensively used in high power applications, it always suffered from being a semi-controlled device. Even though it could be switched ON by applying a gate signal, it has to be turned OFF by interrupting the main current using a commutation circuit. In case of DC to DC and DC to AC conversion circuits, this becomes a serious deficiency with thyristor due to the absence of natural current zero (as in case of AC circuits). Hence, the development of Gate Turn off Thyristor (GTO) addresses the major problem of the thyristor by ensuring the turn OFF mechanism through the gate terminal. A Gate Turn off Thyristor or GTO is a three terminal, bipolar (current controlled minority carrier) semiconductor switching device. Similar to conventional thyristor, the terminals are anode, cathode and gate as shown in figure below. As the name indicates, it has gate turn off capability. These are capable not only to turn ON the main current with a gate drive circuit, but also to turn it OFF. A small positive gate current triggers the GTO into conduction mode and also by a negative pulse on the gate; it is capable of being turned off. Observe in below figure that the gate has double arrows on it which distinguish the GTO from normal thyristor. This indicates the bidirectional current flow through the gate terminal. The junction between the P+ anode and N base is called anode junction.