Gate turn-off thyristor
From Wikipedia, the free encyclopedia
Gate turn-off thyristor (GTO) type of thyristor, a high-power semiconductor device which can be controllaby turned on and off. Usual thyristor (silicon controlled rectifier) is not fully controllable switch, it can be programmably only turned on by gate signal, but after the gate signal is deasserted, it remains in on-state until any turn-off condition occures, which can be application of reverse voltage to the terminals or forward current falls below treshold value known as holding current. Thus usual thyristor behaves like normal semiconductor diode after it is "fired". The GTO can not only be turned-on by gate signal, but also can be turned-off by gate signal of negative polarity.
Turn on is accomplished by positive current pulse between gate and cathode terminals. As the gate-cathode behaves like PN junction, there will be some, but relatively small voltage between the terminals.
Turn off is accomplished by negative voltage pulse between gate and cathode terminals. Some of the forward current (about one tenth) from anode is "stealed" from cathode to gate which results in sequence to forward current fall and switch off.
GTO thyristors suffer from long switch off times, where after main current fall, there is large tail time where residual current flows before all remaining charge from the device is taken away. This restricts the maximum switching frequency to approx 1kHz.
The main applications are in drives and traction.
