Gate turn-off thyristor

The GTO thyristor ( gate turn -off thyristor, English ) is a thyristor coupled to a positive current pulse to the control input as a normal SCR - can be switched on - the gate. In contrast to normal thyristor can be turned off by a negative current pulse ( which is up to one-third of the load current ).

Differences to the normal thyristor

As can be seen the equivalent circuit, there is no difference in the basic structure of a conventional thyristor. Rather, the difference from a normal thyristor in manufacturing, that is, the geometric arrangement of the components on the silicon. In the sectional view of the parallel connection of many thyristors each is visible.

Technology

In principle it would be possible to eliminate even a normal thyristor with a negative current pulse to the gate. A thyristor, however, would only be to " locate " start by the negative gate current, that is, that the silicon area in which a flow of current is possible, is reduced. The remaining current-carrying area would be overloaded and destroy itself.

A GTO thyristor is thus generally divided into as small individual parallel connected thyristors that every single thyristor no longer has the ability to locate, but shall switch off. In parallel circuits, however, there is still the difficulty that all off simultaneously, otherwise the same destruction effect occurs as in conventional thyristors.

Properties

The switch-on of the GTO thyristors is further enhanced by the parallel connection compared to the ordinary thyristor, it is therefore also used where fast turn-on is required, such as in radar systems. It was in these areas, however, almost completely replaced by the advent of the FETs. The biggest drawback of the GTO thyristors is the complex circuitry of the gate terminal. In addition to the fact that the current at the gate can flow in both directions and in a negative direction also becomes very large ( the Abschaltstromverstärkung is very small, so that the turn-off must be up to one-third of the load current ), the current must be limited to avoid destruction.

The thyristors, which can be relatively small for high currents per se, depending on the application need a whole capacitor bank to provide the high currents to turn off. The volume requirement of these capacitors is a multiple of the actual GTO thyristor.

The long Ausräumzeiten for switching off the switching frequency is also limited to about 1 kHz.

Applications

GTO thyristors are used in converters for various purposes, in particular in the power electronics and of the traction systems for electric vehicles. Today, however, they are more and more replaced by IGBTs and will only be used at very high performance.

Developments

• IGC thyristor ( Integrated Gate Commutated Thyristor )
• MTO thyristor
• MC thyristor (MOS Controlled Thyristor )