Gate Turn-Off Thyristors

A number of aspects of gate turn-off thyristors (GTOs) will be discussed, including their historical background, technical demands requiring their development, operating principles, device modeling, design considerations, characterization, gate circuits, and a number of applications to actual equipment. The device design is implemented on the basis of modeling and test-sample experiments. The maximum gate turn-off current is shown to vary proportionally to the factors (VJ1/ρSPB) and WNB, where ρSPB repre­sents the sheet resistivity of the gated p-base layer, and WNB the thickness of the nongated n-base layer. The use of a high doped p-base often leads to excessive re­duction in the current-amplification factor of the n-p-n transistor portion, thus finally deteriorating the overall device performance. In extreme cases, it leads to abrupt in­crease in the on-state voltage, which is theoretically interpreted as resulting from bandgap narrowing. Representative characteristics are given for four types of GTO: 600 V - 200 A, 600 V - 600 A, 1300 V - 600 A, and 2500 V - 600 A units. Research and development activities at different organizations are also briefly reviewed. A num­ber of GTO applications are illustrated, including an 18-kVA VWF inverter for motor-speed control, a 170-kVA power supply for air conditioning, and a 610-kVA VWF in­verter for traction-motor control, both for electric railway coaches. A series of CVCF inverters from 30 kVA to 500 kVA output ratings is also mentioned.