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    Temperature sensing isolated high power components

    What are some good strategies for temperature sensing power components, fets, transformer cores etc, which have high voltages (400V) and are across a safety isolation barrier from the sensing circuit.

    This is a general question, we have applications with both surface mount and through hole (TO-220/247) and I haven't arrived at any solutions that I particularly like from an accuracy, cost and maneuverability perspective.


    I've found some NTC's which are on long wire leads. They're straightforward to glue to whatever I want but they aren't sufficiently insulated for safety. It may be possible to augment them with shrink tubing etc but I don't see a great path there.

    I've also just placed SMT temperature sensing parts (NTC's and I2C type sensors) near my components of interest but safety isolation demands substantial spacing which hurts accuracy and harms the power layout.


    What ideas have other people used?

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    Re: Temperature sensing isolated high power components

    is this a one time do it in the lab, or a permanent,
    put it in lots of sold units per year for many years?

    analog devices AD590 in 2 lead flatpack
    1 microamp per K internally trimmed
    Last edited by wwfeldman; 23rd April 2019 at 20:33.



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    Re: Temperature sensing isolated high power components

    We use a bit of Al-oxide about 2mm x 2mm x 0.8mm thick, with copper on both sides ( DCB ) this way we can solder one side to the middle leg of a HV device ( usually the drain is static ) and solder a thermo-couple to the other side of the DCB - this gives pretty accurate results as the centre leg is the same Cu part that goes thru to the tab on the TO-247 etc ...


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    Re: Temperature sensing isolated high power components

    Quote Originally Posted by wwfeldman View Post
    is this a one time do it in the lab, or a permanent,
    put it in lots of sold units per year for many years?

    analog devices AD590 in 2 lead flatpack
    1 microamp per K internally trimmed
    Ok I know lots of similar devices but what are the tricks for thermally interfacing the temp sensing IC to an isolated high voltage power component?

    Quote Originally Posted by Easy peasy View Post
    We use a bit of Al-oxide about 2mm x 2mm x 0.8mm thick, with copper on both sides ( DCB ) this way we can solder one side to the middle leg of a HV device ( usually the drain is static ) and solder a thermo-couple to the other side of the DCB - this gives pretty accurate results as the centre leg is the same Cu part that goes thru to the tab on the TO-247 etc ...
    Ok interesting. This is a new one to me but to clarify I want a solution I can ship as the functional over-temp detection/shutdown, is this what you use in production or are you describing your lab evaluation technique?



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    Re: Temperature sensing isolated high power components

    For lab testing ...



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    Re: Temperature sensing isolated high power components

    I also was hoping to find something like this, but for measuring the temperature of SMT components. I was hoping to find a chip with an electrically isolated pad which connects to, for example, a DPAK FET's drain tab. Unfortunately I've been unable to find such a thing.

    For measuring components off the PCB, you're going to require some hand assembly. A thermistor and a blob of JBweld would work, if the voltage is not too high...



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    Re: Temperature sensing isolated high power components

    Hi,

    Maybe something in here could be useful/used or be food for thought to inspire an idea, Advanced sensor technologies

    Not sure if this idea is any use or has a whole load of additional complexities that would make the idea untenable and unadaptable for what you're doing: InAs photodiode for low temperature sensing.

    I'm sure it was along the lines of Electronic Design Today, or one of the others of that family of e-magazines, that had an article recently on something or other about using a photodiode or IR LED to sense heat/temperature but don't remember the title of the article, sorry. Maybe sensing IR increase with temperature rise and amplifying with an op amp or something I suspect the theory is nice but reality rather hard to implement successfully or just not feasible for xyz reasons such as wanting to measure a drain pin's temperature, etc.



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    Re: Temperature sensing isolated high power components

    For lab use, a thermal imaging camera is a nice tool. There is special matte black paint you can put where you want to measure with higher precision or on difficult surfaces with high reflectivity.



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    Re: Temperature sensing isolated high power components

    I've found some NTC's which are on long wire leads. They're straightforward to glue to whatever I want but they aren't sufficiently insulated for safety.
    Sorry to not offer much, but that sounds like a good ploy...and feed the NTC circuit to a comparator...and then feed that to a digitial isolator across the isolation barrier...to your micro or whatever is there.



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