AN1379 Datasheet, PDF (4/10 Pages) STMicroelectronics – Z01 and ACS behavior compared under fast voltage transients

Fast transient immunity tests
2
Fast transient immunity tests
AN1379
2.1
Standard requirements and mains filter utility
IEC 61000-4-4 tests propose two different kinds of stress. One, called the “supply test”,
consists of applying the bursts through 33 nF capacitors to the line, neutral, ground or
combinations of these terminals. The second EN61000-4-4 stressing mode is to apply the
bursts through a typical 100 pF capacitor (achieved with an aluminum sheet), directly to the
I/O ports of the system.
The I/O port test is in fact required for systems where there are control wires, as for
computers (wires between the keyboard and the central unit). But appliance manufacturers
perform similar tests to check if their products can withstand fast voltage transients.
For both cases, the system under test is placed 10 cm above the bursts generator reference
plane. As the voltage waveforms increase and decrease respectively in 5 and 50 ns, the
impedance of the parasitic capacitance between the system board and the plane is very low
for such high dynamic waveforms. This results in the application of the major part of the
burst directly across the mains supply plug of the system under test. The following figures
show the line to neutral voltage measured during a 2 kV supply test. We see that the voltage
reaches up to 1.41 kV when no filter is used at the mains input of the system. If a filter, such
as that described in Figure 7, is added, the overvoltage, caused by the 2 kV burst falls to
584 V. This is below the breakdown voltage of most Triacs used in 230 V appliances and of
ACSs. Then, there is no risk of a spurious firing due to turn on in breakover mode.
But Figure 6 also shows that, despite overvoltages being limited, high dV/dt rates are still
present. Indeed, the 500 V overvoltage is reached in less than 10 ns. Silicon devices must
therefore feature a very high dV/dt capability in order to avoid parasitic turn on. The next
paragraph summarizes some comparative analysis made on Triacs and ACSs.
Figure 5. Line to neutral voltage during 2 kV burst without mains filter
1.41 kV
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Doc ID 8317 Rev 5