Steady state output and gate characteristics of a GTO
Steady state output and gate characteristics:
- Steady state output and gate characteristic in the first quadrant is very similar to that of a thyristor. However, the latching current of a GTO is considerably higher than a thyristor of similar rating.
- The forward leakage current is also considerably higher. In fact, if the gate current is not sufficient to turn on a GTO it operates as a high voltage low gain transistor with considerable anode current.
- It should be noted that a GTO can block rated forward voltage only when the gate is negatively biased with respect to the cathode during forward blocking state.
- At least, a low value resistance must be connected across the gate cathode terminal. Increasing the value of this resistance reduces the forward blocking voltage of the GTO.
- Asymmetric GTOs have small (20-30 V) reverse break down voltage. This may lead the device to operate in “reverse avalanche” under certain conditions.
- This condition is not dangerous for the GTO provided the avalanche time and current are small. The gate voltage during this period must remain negative.
- These characteristics are valid for DC and low frequency AC gate currents. They do not give correct voltage when the GTO is turned on with high dia/dt and dIG/dt. VG in this case is much higher.