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ADUM2250 Working Voltage & Regulation Questions

I'm very new to insulation standards, so I have a few questions.

What I'm pretty sure on is our box will need double or reinforced insulation.  We will most likely be using I2C and probably will insulate the rest of the circuit from our high voltage inputs going into an ADE7878.  The plan is to use the ADUM2250 and some other unidirectional iCouplers for the HSDC (high-speed data capture lines) going between the ADE7878 and a microcontroller (and the rest of the circuit).  We'll need a DC-DC converter to get isolated power over to the ADE7878, of course.

Our box will measure up voltages up to 345 V line-to-neutral (600 V line-to-line) on the voltage inputs to the ADE7878.  Readings can be read over Ethernet too.  So it appears our box falls under the IEC 61010-1 standard for test-and-measurement equipment as well as IEC 60950-1 for information technology equipment.

I have a copy of 61010-1 that's about a year old, but from it it seems for basic insulation we need 3,320 VACrms and a clearance/creepage of 5.5 mm. 

# 1. One question I have, do these voltages and clearances differ between 61010-1 and 60950-1?

Looking over the ADUM2250 spec sheet, I see that it has a minimum 7.7mm creepage and 8.0mm clearance.  Since it provides isolation of 5kVACrms too, it appears to meet the needs for basic insulation regarding IEC 61010-1.

# 2. Am I interpreting that correctly?

This FAQ question says that all iCoupler meet at least 400 VACrms but I'm a bit confused because the table seems to imply even for the ADUM225x series that it only supports 400 VACrms working voltage for a bipolar AC waveform, contradicting the spec sheet.  That page doesn't specify which standard that is met either.

# 3. So in order to achieve double insulation, one solution is to put two ADUM2250's back-to-back with isolated supplies from DC-DC converters?

# 4. I'm a little unclear about section 6.5.3 of IEC 61010-1 regarding protective impedances.  Would a pair of resistors in series with the voltage input line count (such as in the voltage divider)?  So you would only need one ADUM2250 along with the resistors?

  • Hello ProgrammerAndy,

    First, there is an update to the IEC61010 standard that is about a year old.  There have been significnt changes to the standard from an isolation point of view.  Make sure you are working to the 3rd edition.

    1) yes this part should meet the requirements for basic insulation under IEC61010 to 5kV

    2) There is somewhat of a disconnect between the agencies test coverage and the long term ability of devices to withstand a working voltage.  The agencies are updating standards slowly, but it is simply too difficult to do a short test that accurately verifies that a part will survive for a given length of time at a particular working voltage.  They rely on the manufacturers to verify lifetime.

    We predict that our parts will last for 50 years at up to 400Vrms working voltage.  Under DC or unipolar AC conditions, our parts will survive higher voltages for that same 50 years.  So we limit the usage of our parts to 400Vac or about 1000Vdc, which may not correspond to the ratings that the agencies provide, since lifetime is not part of the test, and they only specify around 60Hz AC conditions.

    3)The ADuM2250 meets reinforced insulation under IEC60950, so under that standard only one device is required to meet double insulation.  Under IEC61010, 3rd edition, we can only get Basic insulation due to some structural requirements added to the recent version of the standard.  Under that standard, you could probably use two ADuM1250's in series or two ADuM2250's if you liked.

    4) I can't offer a definitive ruling on a system spec, but my reading of IEC61010 is that this applies to accessible parts only, you have to be able to poke the circuit with your finger.  That a limiting resistor between the accessible part and a dangerous voltage is acceptable, or isolation is acceptable, but not both are required.

    I hope this helps,

    MSCantrell

  • Hi Mark

      We're currently about to get some prototype boards made for a project we're working on and are using a fair few ADuM devices from the ADum 440x and ADuM 220x range.

    According to the analog site these have reinforced ratings compliant with 61010, 60601 and 60950 amongst others. (http://www.analog.com/en/interface/digital-isolators/products/quality-assurance/cu_qa_isolators_safety_certificates/resources/fca.html)

    Could you clarify whats actually changed and if Analog are planning new revisions of these families or new families to meet the 3rd edition?

    I'm also rather new to all of this isolation standards stuff and although the company that is going to perform our compliance testing is only using the second edition at the moment (Australia) I'd like to think a bit further down the track, as this system will be in production for quite a few years..

    Thanks

       Richard

  • Hi Richard

    I reviewed the IEC61010 3rd edition standard in detail.  The new standard is written with systems in mind, and does not translate to chop scale devices well.  I am recommending that certification of the system to IEC61010 use section 14.1 clause d.  This allows component level standards to be used for component certification, rather than try to impose a system level standard on the component.  We have VDE0884-10 and IEC60950 to satisfy that clause.  We have had several customer use this approach.

    I hope this helps,

    MSCantrell

  • Hi Mark

      Thanks for that info, we had originally thought we could use 60950 for various parts of our design, however we were informed that the device will fall more into 61010..

    The area in the design where these devices would cross is between the safe control board, and a section of circuitry that is exposed directly to DC voltages of around 200V, eg recording output voltages and currents, driving thyristors etc.

    The 200V side is the output part of a Geophysical transmitter and its driving powersupply, potentially hazardous..

    We'll have a chat to our compliance guys.

    Just out of interest where in the standard exactly is it that these components no longer meet the requirements?

    Thanks

       Richard

  • I would recommend using the VDA0884-10 certificate, since it is a part level standard.  IEC60950 is another system level standard, so the argument for substitution is not as strong.

    MSCantrell