AN1966

Experimental validation example

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Figure 8.

TRIAC turn-on after a 1 kV surge

Figure 9.

TRIAC turn-on and turn-off after a 2 kV surge

Figure 8. shows the overall wave shapes when the circuit in Figure 7. is tested according to

IEC 61000-4-5 standard, with a 1 kV positive surge applied at positive peak line voltage.

This figure shows that the TRIAC is turned on when the surge is applied and remains on

zero just after the surge. This phenomenon is due to the line voltage oscillations coming

from the L-C resonant circuit of the coupler which is used to apply the surge to the line.

Figure 10. shows all the wave shapes at TRIAC turn-on for 2 kV surge. This figure shows

the line voltage increases above 800 V. The load current, i.e the Transil current, is quite high

(4 A) during the voltage clamping, due to TRIAC turn-on delay time.

Figure 11. shows the same but for a -2kV surge applied at negative peak mains voltage.

Here the TRIAC turn-on delay is around 600 ns, compared to 100 ns for the positive surge.

This longer delay is due to the fact that as it’s more difficult to turn-on a TRIAC in quadrant

VT

VLINE

IL

VT

VLINE

IL