GTOs, as opposed to normal thyristors, are fully controllable switches which can be turned on and off by their third lead, the gate lead. Thyristors can only be turned ON using the gate gate turnoff thyristor pdf, but cannot be turned OFF using the gate lead. The GTO can be turned on by a gate signal, and can also be turned off by a gate signal of negative polarity. Turn on is accomplished by a “positive current” pulse between the gate and cathode terminals.
Turn off is accomplished by a “negative voltage” pulse between the gate and cathode terminals. GTO thyristors suffer from long switch off times, whereby after the forward current falls, there is a long tail time where residual current continues to flow until all remaining charge from the device is taken away. It may be noted however, that the turn off time of a GTO is approximately ten times faster than that of a comparable SCR. Comparison of an SCR and GTO of same rating. PN layers in the drift region to reshape the field profile and increase the voltage blocked in the off state.
Compared to a typical PNPN structure of a conventional thyristor, the DB-GTO thyristor has a PN-PN-PN structure. GTO thyristors are available with or without reverse blocking capability. Reverse blocking capability adds to the forward voltage drop because of the need to have a long, low doped P1 region. GTO thyristors capable of blocking reverse voltage are known as Symmetrical GTO thyristors, abbreviated S-GTO. Usually, the reverse blocking voltage rating and forward blocking voltage rating are the same. The typical application for symmetrical GTO thyristors is in current source inverter. GTO thyristors incapable of blocking reverse voltage are known as asymmetrical GTO thyristors, abbreviated A-GTO, and are generally more common than Symmetrical GTO thyristors.