Author Topic: "Floating" Copper Pours on PCB - LED Thermalplane  (Read 2727 times)

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Offline David

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"Floating" Copper Pours on PCB - LED Thermalplane
« on: January 31, 2013, 11:17:05 am »
Hi all,

I have designed an LED strip (300x20mm) which consists of 3 LEDs plus some resistors/Zeners and a connector. The LEDs have a thermal pad which I have connected to large copper pours (essentially fill both side of the strip) on both the top and bottom of the PCB. The thermal plane is stitched together directly under the thermal pads on the LED with vias as well as through other holes. The thermal performance is very good and there are no problems there. However I have been thinking about EMC and floating copper pours. Should I connect the thermalplane to ground? (Assuming this has no effect on LED operation). The LEDs are driven by a ~350mA C.C. 230Vac flyback supply.

Best Regards,

Dave
David
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Electronics Design Engineer
 

vlf3

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Re: "Floating" Copper Pours on PCB - LED Thermalplane
« Reply #1 on: January 31, 2013, 04:00:20 pm »
Have you monitored on a radio, LF to HF Short-wave bands for any RFI being emitted... however, it might be a good option to ground the PCB plane, since any AC present will radiate along the LED strip, and find it's own resonance.
 

Offline Corporate666

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Re: "Floating" Copper Pours on PCB - LED Thermalplane
« Reply #2 on: January 31, 2013, 06:36:07 pm »
Have you looked at the LED datasheet for info on this?  I've seen some specifically mention that the thermal pad should not be connected to ground. 

If that's not an issue, I don't see why connecting to ground would hurt.
It's not always the most popular person who gets the job done.
 

Offline SeanB

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Re: "Floating" Copper Pours on PCB - LED Thermalplane
« Reply #3 on: January 31, 2013, 06:57:17 pm »
If it is connected to an internal part of the die ( very common to have it be part of the one lead) then use a small 1n or so ceramic capacitor and a 1M chip resistor in parallel to connect it to the one power lead, so as to prevent radiation from it.
 

Offline David

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Re: "Floating" Copper Pours on PCB - LED Thermalplane
« Reply #4 on: February 01, 2013, 09:38:16 am »
I have checked the datasheet and the pad is electrically isolated from the anode/cathode. I have decided to connect the thermal planes to ground.

I now have another silly question...should I connect the mounting holes to ground too? The PCBs will sit on an earthed metal tray.
David
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Electronics Design Engineer
 

Offline David

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Re: "Floating" Copper Pours on PCB - LED Thermalplane
« Reply #5 on: February 01, 2013, 10:16:07 am »
I am thinking I should isolate them as this could introduce common mode noise?
David
(United Kingdom)
Electronics Design Engineer
 


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