SLYY063A October   2014  – May 2026 ISO5451 , ISO5452 , ISO5851 , ISO5852S , ISO6420 , ISO6421 , ISO6441 , ISO6463 , ISO7810 , ISO7820 , ISO7821 , ISO7830 , ISO7831 , ISO7841 , ISO7842 , ISOW1050 , ISOW3080 , ISOW6441 , UCC5310 , UCC5320 , UCC5350 , UCC5390

 

  1.   1
  2.   FAD
  3.   Understanding the definitions of high-voltage isolation parameters, their relevance to real applications, and the methodologies used to test them, allows systems engineers to pick the right isolator for their design need.
  4.   Maximum transient isolation voltage and isolation withstand voltage
  5.   Maximum repetitive peak voltage and working voltage
  6.   Maximum surge isolation voltage
  7.   Comparative tracking index
  8.   Distance through insulation
  9.   Conclusions
  10.   References
  11.   Appendix

Maximum surge isolation voltage

Maximum surge isolation voltage (VIOSM) quantifies the ability of the isolator to withstand very high voltage impulses of a certain transient profile. The surge test profile is shown in Figure 4 . Surge voltages can be caused in an installation due to direct or indirect lightning strikes, faults and short circuit events. As per IEC 60747-5-5 and VDE 0884-10, an isolator claiming a certain VIOSM must pass the surge test at a peak voltage of 1.3 times VIOSM for basic isolation, and 1.6 times VIOSM for reinforced isolation. An isolator can be called reinforced at the component level, only if it passes the surge test at a level greater than 10 kV.

The passing level of a surge test is also used to determine compliance to system-level standards, such as the IEC 61800-5-1, that require a certain level of surge capability for a given system voltage. For example, for equipment connected directly to supply mains (known as category III), operating at 600 Vrms line voltages, IEC 61800-5-1, requires a minimum surge capability of 8000 V for reinforced isolation.

Note that passing a surge test at levels greater than 10 kV has been widely used as the gold standard for reinforced isolation, though system level standards allow for lower values of surge capability for systems with lower line voltages.

Surge impulse profile. Figure 4 Surge impulse profile.

Figure 5 shows the setup used to test surge performance on the ISO7842. The isolator is configured as a two-terminal device by shorting all the left-side pins to one group, and all right-side pins to another group. Surge voltage is applied across the isolation barrier using either the MIG1203 or the MIG2403 surge generators, depending on the test voltage required.

Surge test setup. Figure 5 Surge test setup.

The test is performed by applying 50 pulses each for both positive and negative polarities of the rated stress voltages. After the surge test, a partial discharge test per method B1, insulation impedance test and a full functional production test are performed on the device. A device is considered to pass the surge test if it successfully passes all these tests after applying the surge voltage. To avoid arcing through the air, this test is performed in dielectric oil.

Based on testing on greater than five wafer lots, and a total of more than 2000 devices, the ISO7842 passes the surge voltage test at greater than 12800 V. Since this exceeds 10 kV, it meets the limit for reinforced isolators. The rated value of VIOSM is 8000 V, according to the scaling factor of 1.6 required for reinforced isolation. Passing a 12800 V surge test also implies that this device meets the surge criterion for reinforced isolation for equipment connected directly to supply main, for line voltages up to 1000 Vrms, as per IEC 61800-5-1.