I'm wondering what to connect the thermal pad on the bottom of the leds too, it appears to be connected to the VCC side of the red chip in the led. I will be running them in series so I can't connect the three heat pads to a common plane in the pcb.
I'd like some suggestions on how to do this, the PCB in the first link I posted is hard to examine what the heatsink pads are connected too, but they look like they are all on the same plane?
I have not been able to find information from the manufacturer of your LED, but on all Lumileds, the Heatsink pad needs to be floating, and connecting it to either Cathode or Anode will hurt the LED over time.
So make a big copper-fill for heatsinking, but do not connect to any of the other terminals.
dtokez:
Thanks for the help. The only thing is I will have to make 3 separate heat sink pads since I'm connecting the 3 LED'son the board in series, I guess?
dtokez:
Thanks for the help. The only thing is I will have to make 3 separate heat sink pads since I'm connecting the 3 LED'son the board in series, I guess?
No you can have a common heatsink but the seprate LEDs pads coupled thermally but isolated electrically. This is done by washers or pads that are insulators electrically but have a good thermal conductivity.
Mica used to be used but these days there are composite materials you can use.
Zapro:
I have not been able to find information from the manufacturer of your LED, but on all Lumileds, the Heatsink pad needs to be floating, and connecting it to either Cathode or Anode will hurt the LED over time.
Can you provide a reference for that statement? I've never seen any recommendation that the thermal pad of this type of LED (or similar LEDs) needs to be kept electrically isolated from the anode or cathode. I've never done that myself and never encountered any problems.
Zapro:
I have not been able to find information from the manufacturer of your LED, but on all Lumileds, the Heatsink pad needs to be floating, and connecting it to either Cathode or Anode will hurt the LED over time.
Can you provide a reference for that statement? I've never seen any recommendation that the thermal pad of this type of LED (or similar LEDs) needs to be kept electrically isolated from the anode or cathode. I've never done that myself and never encountered any problems.
The anode side of the device is denoted by a hole in the lead frame. Electrical insulation between the case and the board
is required—slug of device is not electrically neutral. Do not electrically connect either the anode or cathode to the slug.
Looking at the descriptions of the construction of these "beads" it looks like the thermal slug is intended to be electrically isolated but not guaranteed. Definitely some food for thought there.