Electromagnetic compatibility standards

AN1172

14/23

Figure 14.

IEC 61000-4-4 test synopsis

Figure 15. shows the OUT-COM voltage measured during a 2 kV IEC 61000-4-4 test (N.B.:

1 kV is required for public power network). We see that in spite of capacitive current due to

high dV/dt rates, the ACS does not turn-on. The semiconductor switch withstanding to IEC

61000-4-4 depends on its dV/dt capability. ACS devices present dV/dt characteristics ten

times greater than both same current and sensibility ratings triacs. For example, a 10 mA

It can also be seen that the ACS voltage overflows its breakdown value given for a 50 Hz

sine wave (810 V is reached in spite of 650 V breakdown value). In fact, the voltage rate of

increase is so high that the silicon device has not enough time to begin to clamp. A higher

Figure 15.

IEC 61000-4-4 test on ACS402-5 cell for a 2 kV burst

To sum up, it can be said that ACSs, thanks to their high dV/dt capability, improve the overall

electronic board robustness towards fast line transients without any snubber. But it must be

kept in mind that the mains filter Y2 capacitors play also a role in sustaining IEC 61000-4-4

tests, by derivating some part of the bursts energy. The typical values of these capacitors

are 2.2 nF.

10 cm

10 cm

100 pF

Ground Reference

Mains

Filter

IEC1000-4-4

Generator

High Voltage

Output

25 W light bulb

Test board

220

Ω

COM

Ω

Ω

Ω

220

220

220

Y2

Iout (1 A/div)

Vout (250 V/div)