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johnsmith1212

150W LED streetlight....why dont they use the streetlight superstructure as heatsink?

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Hello,
The following below document (RDR-32) is for a 150W PFC’d LED streetlight.
Its noticeable that the schematic on page 8 simply shows the earth connection being simply connected directly to the neutral. Surely this is not wise as RCD’s could be tripped?

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Surely for the sake of common mode noise mitigation, it would be best to have Y capacitors from live and neutral being connected to the earth connection? The schematic on page 8 shows no Y capacitors in the mains input section. Isn’t this a missed trick?  

Another point is that in a streetlight, the pole itself is earthed, and the streetlight head itself is inevitably metal and is directly fasted to the earthed pole. In other words, the metal casing of the streetlight head is also earthed. It surely makes sense, to use the metal head of the streetlight as a heatsink. –If one does not do this, then one has to isolate the metal head of the streetlight from the earthed pole, and surely this is a waste of time?

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Anyway, the RDR-32 document never speaks about using the earthed streetlight metal as a heatsink. Indeed, for the PFC stage, it recommends heatsinking the Boost FET and diode bridge to primary side DC bus ground. –Surely this is missing a trick?......i mean, you have a big chunky metal streetlight head, why haven’t they used it is a heatsink? 

Is it because they fear getting more common mode noise if they use an earthed heatsink for heatsinking the power switching FETs? Even then, surely it would be best to still use the earthed streetlight enclosure as a heatsink, and then just use a bigger common mode choke in order to mitigate the common mode noise problem?

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I mean, they have a big metal streetlight..why are they not using the streetlight superstructure itself as the heatsink?...i mean..it’s going to be there anyway. I appreciate that its earthed but earthed heatsinks are not at all uncommon.

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