AN302 datasheet(7/10 Pages) STMICROELECTRONICS

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AN302

Holding current - the details

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Figure 7.

Relative variation of IH, with the junction temperature, Tj

2.2.3

Effect of reapplied voltage

The rise time and the level of the reapplied reverse voltage across the TRIAC after blocking

have no effect on the value of its holding current, IH.

2.2.4

Influence of the external gate cathode resistor

Figure 8.

Variation of IH, of a sensitive thyristor with RGK

Some applications require a resistor, RGK, to be connected between the gate and the

cathode of the component, either to improve its behavior under voltage at high junction

temperatures (by-pass for leakage current) in the case of sensitive thyristors or because it

forms part of the firing circuit. The value of this resistor, as well as the sensitivity of the

component, affects the holding current as shown in Figure 8.

Sensitive thyristors (IGT < 200 µA)

For sensitive thyristors RGK has a large influence on the holding current as shown by

Figure 9. Thus, in certain applications, the designer may want to use a high-impedance

control circuit.

Standard thyristors, sensitive and standard TRIACs

Here, RGK has no significant effect on the holding current provided that it is not too low, that

is, RGK should be greater than 20 Ω.

Note: The hypostatic current for sensitive thyristors is always specified for R

GK = 1000ohms.

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