IGCT/GCT

1. IGCT (Integrated Gate Commutated Thyristor) is an ABB product, GCT ic by Mitsubishi, but the concept is the same. Here Turn-off time is very low.
2. Power consumption by the GCT driver is greatly reduced compared with that of a conventional GTO driver.
3. The key to achieving a hard-driven or unity-gain turn-off condition lies in the gate current commutation rate. If the gate driver of a GTO is very fast so the gate current can increased rapidly to the anode current level and the cathode current decreases to zero before the anode current begins to decay. A rate as high as 6KA/µs is required for 4-KA turn-off.
4. One method for the implementation of a hard-driven GTO, is to hold the gate loop inductance low enough (3 nH) that a DC gate voltage less then the breakdown voltage of the gate-cathode junction (18 to 22 V) can generate a slew rate of 6 KA/µs. This approach is used in the IGCT/GCT, where a special low-inductance GTO housing and a carefully designed gate driver meet this requirement. The power consumption by the GCT driver is greatly reduced compared with the conventional GTO driver, since the gate current is present for a much shorter period of time. Figure shows the external view of the two commercially available GCTs.
5. The key disadvantage of the GCT approach is the high cost associated with the low-inductance housing design for the GTO and the low inductance and high current design for the gate driver.

GCT operation principle and two GCTs developed by Mitsubishi and ABB (Photographs courtesy of Mitsubishi (top) and ABB (bottom).)

Impact of switching speed

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