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Is it okay if thyristor is on when GT current and voltage on shaded range?

Latest Updated:07/01/2008

Question:

The gate trigger characteristics of the 8P4SMA define the gate trigger current as IGT = 10 mA max. and the gate trigger voltage as VGT = 1.5 V max (when Tj = 25°C). The following figure also shows an example of the gate characteristics.
As these are maximum ratings, is it all right to consider that the thyristor turns on if the gate trigger current and voltage are within the shaded range in the figure?

Answer:

No, it is not.
These are the maximum ratings of the worst-case characteristics. Be sure to design a circuit where a higher current can flow and voltage can be applied when the product is actually used.
The shaded part on the figure indicates that the characteristics of all these products are distributed within this range.
Note that a PN-junction diode is configured between the gate and cathode of the thyristor. The characteristics between the gate and cathode therefore include elements of parallel resistance and series resistance that adjust the gate sensitivity.
Both the gate trigger current and voltage must be taken into consideration when determining how to turn on the thyristor. However, the value of the voltage is the value that occurs incidentally between the pins when the current flows. To turn on the thyristor, therefore, a current higher than the maximum value of the gate trigger current must flow.
If the supply voltage that causes the current to flow is lower than the rated gate trigger voltage at this time, the gate trigger current cannot flow properly.
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