Standards for Magnetic and Capacitive CouplersNovember 27, 2020 by Wolfgang Frank
This article highlights Infineon Technologies superior isolation capability of the coreless-transformer technology allows testing its new EiceDRIVER™ isolated gate driver ICs 1ED34xxMx12M, 1ED38xxMx12M, and 1ED31xxMx12H
The German preliminary standard VDE V 0884-11:2017-01 has specified the requirements regarding reinforced and basic isolation for magnetic and capacitive couplers since 2017. Now, the IEC has published an international standard that is based on the VDE V 0884- 11. This article explains the difference between the new IEC 60747-17:2020 Ed. 1 and the VDE V 0884-11. It also outlines the improvements that have been made with regard to photocouplers and the relevant photocoupler standard IEC 60747-5-5:2020 Ed.2.
The preliminary standard, VDE V 0884-11, which succeeded its predecessor VDE V 0884-10:2006-12 in January 2017, defined for the first time strict requirements regarding lifetime predictions of the isolation. Such requirements are part of the new international standard IEC 60747-17, as are safety-promoting improvements concerning photocouplers. Table 1 shows the most important differences.
|Standard and scope||IEC 60747-17 Magnetic/ capacitive||VDE V 0884-11 Magnetic/ capacitive||IEC 60747-5-5 Photocoupler|
|End-of-life modeling for isolation||yes||Yes||No|
|Safety factors for end-of-life model||yes||Yes||No|
|Improvements of isolation and partial discharge (PD) test||yes||No||No|
|V_IOSM / V_IMP||yes/yes||Yes / no||Yes / no|
Table 1: Comparison of contents with respect to various coupler standards
The method for modeling the end-of-life (EOL) for the isolation barrier was adopted from VDE V 0884-11. High-voltage stress tests at three different voltage levels according to figure 1 are the basis of the EOL model. Furthermore, the expected time-to-failure at these three voltages have to span at least two orders of magnitude. The resulting data are the basis for the extrapolation to evaluate the isolation ratings of the “maximum rated repetitive peak isolation voltage” VIORM of the coupler. The model itself necessarily aims at a total time-to-failure of at least 20 years. In addition, various safety factors are included, which are also indicated in figure 1:
• Safety factor for the time-to-failure of 1.5 for reinforced isolation and 1.2 for basic isolation
• Safety factor in voltage (VIORM) of 1.2
• In addition to all the safety margins, the model assumes a failure rate at EOL of 1 ppm after 20 years for reinforced isolation.
Improvement of isolation and partial discharge test
An improvement in the new international standard IEC 60747-17: 2020 Ed. 1 over VDE V 0884-11 and the photocoupler standard IEC 60747-5-5: 2020 Ed. 2 is the method used for testing the isolation and partial discharge (PD) in the production of the couplers. Each coupler undergoes PD testing, which screens potential weak parts. It is now mandatory to combine the isolation test and the PD test in a single test procedure as depicted in Figure 2. The isolation type test first applies the rated isolation voltage to the device under test (DUT) for 1 minute.
Figure 1: Principle for end-of-life extrapolation
It is important to point out here that the isolation test voltage is higher than the PD inception voltage Vinc. This forces a limited partial discharge but does not lead to a break down. The test voltage decreases after the isolation test to the specified PD measurement voltage level Vpd(m). The PD measurement voltage level is lower than the so-called “partial discharge extinction voltage” Vext. PD has to be eliminated at Vext. Parts can be screened out that still show excessive PD. Thus, it is mandatory that PD happens during isolation test to be sure, that PD disappears at the right places.
Infineon has installed method b1 of figure 2 for routine tests in production for certified EiceDRIVER™ products. The above mentioned test methods are superior to the method shown in figure 3, which is often used for photocouplers , . That particular method allows an undefined time between the isolation test and the PD test. The forced partial discharge event is “extinct”, of course, when the stress voltage goes down to zero. In addition, potential free charges can recombine in the insulation, so that almost every DUT can pass the PD test , .
PD test levels at Infineon
The new standard IEC 60747-17 requires a measurement voltage level of Vpd(m) = 1.875∙VIORM during the partial discharge test interval. This level is the industry standard for many suppliers. However, the well-known coreless-transformer technology from Infineon can pass much higher partial discharge measurement levels Vpd(m), as seen in Table 2. Consequently, Infineon plans to use this superior isolation technology and exclusively measures at higher levels of Vpd(m) = 4500 V (peak).
Figure 2: Principle of the combined isolation and partial discharge test:
a) method a (used for type tests)
b) method b1 (used for routine tests)
c) method b2 (alternative for routine tests)
This is 100% routine test to be performed on the next generation of certified EiceDRIVER™ series such as 1ED34xxMx12M, 1ED38xx- Mx12M, and 1ED31xxMx12H. The most important ratings for such gate-driver ICs are also given in Table 2 based on available results. The maximum rated repetitive peak isolation voltage VIORM is planned for 1767 V peak. This value represents a new level of isolation performance of magnetically isolated couplers.
Figure 3: Not allowed PD test method in IEC 60747-17
|Parameter / rating
|Vpd(m)||4500 V (peak)||4500 V (peak)|
|VIORM (reinforced)||1767 V (peak)||1767 V (peak)|
|VIOSM (test level)||11000 V (peak)||11000 V (peak)|
|VIMP||8000 V (peak)||8000 V (peak)|
Table 2: PD test voltage levels and certification ratings (planned) of Infineon gate driver ICs
New rating for external isolation capability
The clearance distance of a coupler’s package defines the external isolation capability. The clearance should provide those dimensions that are important for meeting the application’s needs. However, the VDE V 0884-11, as well as the photocoupler standard IEC 60747-5-5, require a surge voltage above 10 kV for a reinforced certificate. This voltage level ensures that the internal isolation barrier is strong enough. Small packages cannot pass this test if their clearance distance is shorter than that defined by IEC 60664-1:2020 Ed.2, Table F.2. Therefore, one can perform the surge voltage testing in isolation oil. It enables couplers in smaller packages to obtain a reinforced isolation certificate. IEC 60747-17:2020 specifies the surge isolation voltage VIOSM as the rating for the internal isolation.
The new rating is the external isolation voltage rating, which is specified by the impulse voltage VIMP. The naming of this rating has been inspired by the impulse withstand voltage as per IEC 60664-1:2020. The surge voltage test has to be conducted in the air as the coupler is normally used in the application and no flashover shall be detected. Alternatively, the impulse voltage can be derived from the clearance requirements of IEC 60664-1:2020, Table F.2.
The new international standard IEC 60747-17:2020 overcomes weaknesses in comparison with its predecessor standards and photocoupler standards. It allows only those PD test methods, which have a proven physical background. This ensures that no weak parts find their way into commercial devices. Infineon adopted the combined isolation and partial discharge testing right from the start. The superior isolation capability of the Infineon coreless-transformer technology allows testing its new EiceDRIVER™ isolated gate driver ICs 1ED34xxMx12M, 1ED38xxMx12M, and 1ED31xxMx12H at much higher partial discharge measurement voltage levels compared to the minimum requirements of the new standard. This ensures the industry benchmark quality of Infineon’s gate-driver ICs.
 IEC 60747-17:2020, Magnetic and capacitive coupler for basic and reinforced insulation; International electrotechnical commission, Geneva, Switzerland, 2020.
 VDE V 0884-11:2017-01, Semiconductor devices - Part 11: Magnetic and capacitive coupler for basic and reinforced isolation, Beuth-Verlag, Germany, 2011.
 IEC 60747-5-5:2020, Semiconductor devices – Part 5-5: Optoelectronic devices – Photocouplers, International electrotechnical commission, Geneva, Switzerland, 2020.
 Vishay: “Optocoupler for Safe Electrical Isolation to DIN EN 60747- 5-2 (VDE 0884)/DIN EN 60747-5-5 Pending; Application note, VISHAY SEMICONDUCTORS, Document Number: 83707, Rev. 1.4, 2011.
 To shiba: “Safety Standards for Photocouplers”; Application note, Toshiba Electronic Devices & Storage Corporation, Toshiba, Rev.1.0, 2018.
About the Author
Wolfgang Frank is the principal engineer for product definition and concept of gate driver ICs at Infineon Technologies. Earning his degree in power engineering from Technical University, Munich, he has worked in power engineering for over 20 years.
Heiko Rettinger worked at Infineon Technologies AG