AN4030

Conclusion

Doc ID 022635 Rev 1

13/15

3

Conclusion

To increase power semiconductor device immunity to fast transient voltages it is quite

common to add a capacitor between the control terminal (gate or base) and the drive

reference terminal (source, emitter, cathode or A1 terminal). For SCRs, the drive reference

is the cathode, K. A gate to cathode capacitor is then usually added with very sensitive

devices and could be very useful to increase SCR immunity to dV/dt.

This Application note shows that as well as being almost ineffective in improving Triac

immunity, a gate to cathode capacitor has a major drawback when operating with Triacs.

Such a capacitor increases the failure rate when repetitive dI/dt rates are applied at turn-on

or in case of spurious turn-on with high dI/dt.

Explanations of silicon structure behavior during turn-on show the supplementary stress

due to a gate to cathode capacitor irrespective of technology choice. This shows that such

capacitors should be removed from Triac designs.