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  1. #1
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    Non-isolated offline LED driver with LED MCPCB screwed to earthed heatsink

    Hello,
    We have an 230VAC offline, non-isolated LED driver with a 300V LED bank.
    The LEDs are on MCPCB, which is screwed down to an earthed heatsink.

    Can you confirm that this is illegal?, since if the earth wire that connects to the heatsink was (for whatever reason) not secured, then the heatsink would be insufficiently insulated from live mains.

    So….we are using the same sort of setup as on Figure 3 on page 4 of the following App Note on LED MCPCB’s..
    http://www.lumileds.com/uploads/539/AB06-pdf

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    Re: Non-isolated offline LED driver with LED MCPCB screwed to earthed heatsink

    Can the heat sink be touched by somebody or get in contact with unearthed metal parts?

    Why do you expect disconnection of protective earth?

    The MCPCB must provide basic insulation for 300 V in any case, if you can achieve reinforced insulation, heat sink earthing isn't necessarily required.



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    Re: Non-isolated offline LED driver with LED MCPCB screwed to earthed heatsink

    Can the heat sink be touched by somebody or get in contact with unearthed metal parts?
    Thanks, yes, a worker could be up the pole and could touch the heatsink. The outside of the heatsink is painted, but the paint could corrode away.
    Why do you expect disconnection of protective earth?
    I was just thinking that the screw that connects the earth wire to the heatsink could in theory vibrate loose in transit, and if the assemblers forgot to glue the screw, then the heatsink-earth connection would be gone.

    - - - Updated - - -

    -------------------------------------------------------------------------
    .....the thing is, on page 9 of the following …

    http://www.lumileds.com/uploads/539/AB06-pdf

    …it states that there should be 2mm of clearance from an MCPCB copper trace and the board edge.

    …The thing is, if the MCPCB is screwed directly to an earthed heatsink, then the MCPCB copper traces may just as well be right at the board edge, because wherever the PCB traces are, they are effectively only a few microns away from the earthed heatsink? (a few microns being the thickness of the dielectric insultion layer on the MCPCB).

    Also, i dont think a few microns of MCPCB insulation is classed as being sufficient insulation from the mains?



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    Re: Non-isolated offline LED driver with LED MCPCB screwed to earthed heatsink

    "could", "would", "I was just thinking"...

    The problem should be analyzed in terms of applicable safety standards rather than inventing new requirements.



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    Re: Non-isolated offline LED driver with LED MCPCB screwed to earthed heatsink

    Thanks, -do you agree that in our case, restricting the MCPCB copper traces to more than 2mm from the edge of the MCPCB (as discussed in post #3) would be completely pointless?

    - - - Updated - - -

    Thanks, indeed , Germany is the only country in the world that has “got a grip” when it comes to safety standards. –Perhaps also the USA to an extent. In my experience, the Germans know the meaning of the word “teamwork”. In the UK engineering industry, we do not understand this word.
    The Germans understand that to share ones knowledge of stuff like electrical safety standards, with other German companies, (even German competitor companies) results in a better situation for all electrical co’s, and all benefit from the increased economic prowess that results from it. In UK , we do not know what it means to share knowledge with a fellow UK company. In UK, the goal is to destroy other UK companies, in an aim to be the main player in the market.
    In our small company, we cannot afford to buy the safety standards, and do not know where to find which exact standard tells about this.

    - - - Updated - - -

    Page 4 of the doc in the top post speaks of EN60598, but we cant remember its exact words from when we previously read it , and cant afford to now buy it

    - - - Updated - - -

    --------------------------------------------------
    Page 4 of the doc in the top post ..also linked here.;
    http://www.lumileds.com/uploads/539/AB06-pdf
    ..appears to state that, for an MCPCB, if the LED voltage is non-isolated and/or >120V, then a bare bit of copper must exist on the MCPCB for the purpose of connecting a probe to it so that a high voltage insulation test can be done….between the MCPCB trace and the earth ground.
    Is this correct?

    - - - Updated - - -

    -------------------------------------------------
    I think in our case, the law is that insulated screws (made of plastic or bakolite) must be used to screw the MCPCB to the Earthed heatsink. Also, I believe that a separate “rubber” insulating pad must be used between the MCPCB and the earthed heatsink. Do you agree?
    We cannot phone up a fellow UK competitor company and request advice on this, because they will tell us to “go drop dead”. –in the UK, it is not like in Germany where competitor companies correctly realise the benefits of actually helping your competitors.



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    Re: Non-isolated offline LED driver with LED MCPCB screwed to earthed heatsink

    ...then a bare bit of copper must exist on the MCPCB for the purpose of connecting a probe to it so that a high voltage insulation test can be done
    A hipot test can be usually performed between mains terminals and heat sink.

    I generally disagree with your conclusions about specific design requirements. There are different ways to achieve sufficient creepage and clearance. If you see the discussed design details in an approved product, consider that it may be one of the possible solutions.



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    Re: Non-isolated offline LED driver with LED MCPCB screwed to earthed heatsink

    I worry about all this...
    No brainer 1, the heatsink should be isolated from the PCB and any high voltage traces, this is a given and should be covered during the design cycle, you dont rely on the solder resist coating of a PCB!

    - - - Updated - - -

    Thanks, indeed , Germany is the only country in the world that has “got a grip” when it comes to safety standards. –Perhaps also the USA to an extent. In my experience, the Germans know the meaning of the word “teamwork”. In the UK engineering industry, we do not understand this word.
    The Germans understand that to share ones knowledge of stuff like electrical safety standards, with other German companies, (even German competitor companies) results in a better situation for all electrical co’s, and all benefit from the increased economic prowess that results from it. In UK , we do not know what it means to share knowledge with a fellow UK company. In UK, the goal is to destroy other UK companies, in an aim to be the main player in the market.
    In our small company, we cannot afford to buy the safety standards, and do not know where to find which exact standard tells about this.

    RUBBISH


    Lastly if you cant afford a spec for a product you are designing then I am lost for words!



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    Re: Non-isolated offline LED driver with LED MCPCB screwed to earthed heatsink

    No brainer 1, the heatsink should be isolated from the PCB and any high voltage traces, this is a given and should be covered during the design cycle, you dont rely on the solder resist coating of a PCB!
    Thanks, i am certain that even though the dielectric in MCPCB is rated to 1.5kv, we will still need an insulation pad between the mcpcb and the earthed heatsink?



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