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ISO7841: Reinforced isolation in DC application?

Part Number: ISO7841

We are using the ISO784xFDWW parts in a DC application we want to upgrade from 1000V to 1500V, and since we have low-level controls on one side, we need reinforced isolation. 

The parts are rated for 1450VRMS (reinforced, 60950-1, pollution degree 2, material group I).

Assuming that the 1450VRMS refer to a mains frequency (50/60Hz) sinusoidal waveshape, how does the rating translate to a DC application? 

(Calculating the RMS-value of a DC is the easiest thing in the world, but differences in stress-factor between AC and DC can differ in both directions...). 

Looking at the datasheet, the 800V/1450V (DW(DWW) ratings are 1:1 with the clearance and creepage figures (">8mm" / ">14.5mm"). If these are indeed the limiting parameters on the reinforced isolation voltage, we should be able to reach the requirements with a suitable combination of slotting, coating and/or potting (?)

Thanks in advance

Christian Nielsen 

  • Hi Christian,

    Thanks for posting your questions on E2E forum!

    I'll address your questions below:

    Q: Assuming that the 1450VRMS refer to a mains frequency (50/60Hz) sinusoidal waveshape, how does the rating translate to a DC application? 

    A: Intrinsically, the ISO784xDWW devices are able to withstand much higher DC working voltage than AC voltages; for example the intrinsic DC working voltage for ISO7841DWW is 2828 V (shown on page 8 of the data sheet). Of course, this voltage is then further limited by the equipment standard (for example, IEC 60950-1) requirements such as Creepage, Pollution Degree, etc.

    Q: Looking at the datasheet, the 800V/1450V (DW(DWW) ratings are 1:1 with the clearance and creepage figures (">8mm" / ">14.5mm"). If these are indeed the limiting parameters on the reinforced isolation voltage, we should be able to reach the requirements with a suitable combination of slotting, coating and/or potting (?)

    A: Yes, the IEC 60950-1 voltages are limited by the Creepage, Clearance and other limitations in this standard. If you can reach the requirements with a suitable combination of slotting, coating and/or potting, that's perfectly acceptable.

    Thanks,

    Saleem Marwat