GTO has many parameters identical to thyristors. Only some parameters different from thyristors are introduced here.
(1) Maximum turn-off anode current IATO
When the current is too large, the condition that α1+α2 is slightly larger than 1 may be destroyed, and the saturation of the device is deepened, resulting in failure of the gate turn-off.
(2) Turn off gain
Off
GTO turn-off gain
Off is the ratio of the maximum turn-off anode current IATO to the gate negative current maximum IgM,
Off is usually only about 5.
Gate drive circuit and snubber circuit
1. The main factors that can affect the GTO conduction of the gate drive circuit that can turn off the thyristor are: anode voltage, anode current, temperature and gate trigger signal. The anode voltage is high, GTO is easy to conduct, and it is easy to maintain large-area saturation conduction when the anode current is large. When the temperature is low, it is necessary to increase the gate drive signal to obtain the same conduction effect as at room temperature.
(1) Requirements for the gate trigger signal Because the GTO operates in a critical saturation state, the gate trigger signal is large enough.
The steeper the pulse front (positive and negative pulses), the better, and the trailing edge is smoother. A positive pulse trailing edge is too steep to produce a negative spike; a negative pulse trailing edge is too steep to produce a positive spike, which will reduce the withstand voltage of the GTO just turned off and the d/dt experienced by the anode.
In order to achieve strong triggering, the gate positive pulse current is typically (3 to 5) times the rated trigger current (DC).
(2) Gate trigger mode
There are usually three types of GTO gate triggering methods:
1 DC trigger During the GTO is triggered to turn on, the gate always has a DC trigger signal.
2 Continuous pulse triggering During the GTO being triggered to conduct, the continuous trigger pulse is still added to the gate, so it is also called pulse train trigger.
3 Single pulse trigger is the common pulse trigger. After GTO is turned on, the gate trigger pulse ends. The forward tube pressure drop of GTO is small with DC trigger or pulse train trigger mode. When using single-pulse triggering, if the anode current is small, the tube voltage drop is large. When triggered by a single pulse, the leading edge steepness of the pulse should be increased, and the pulse amplitude and width should be increased to make most or all of the GTO reach saturation guidance. Pass status.
An effective method for absorbing the overvoltage by the snubber circuit is to connect a resistor-capacitor circuit that absorbs the overvoltage in parallel across the device. If the parameters of the absorbing circuit components are not properly selected, or if the wiring is too long and the distributed inductance LS is too large, a serious overvoltage may occur.
The selection of the snubber circuit components should be a small RS, and the resistance of the RS should generally be 10 Ω to 20 Ω. RS should not be wire-wound, but should be a non-inductive resistor made by the coating process. It is required that the diode VDS can be turned on quickly, the reverse recovery time trr is short, and the reverse recovery charge Qr is as small as possible. The CS in the sink circuit should also be a non-inductive component to minimize the stray-distribution inductance LS of the sink circuit.
