Do COB LEDs usually need electrically insulating from the heatsink?

Question

I have some Vero series LEDs from Bridgelux. I want to put multiple LEDs on 1 heatsink. I was planning to use thermal epoxy, so there is the possibility of the aluminium base of the LED touching the metal heatsink.

I have looked through the data sheet and all application notes. I can't see any reference to electrical isolation between the LED power and the heatsink. Is this because it is standard for these type of LEDs to have electrical insulation between the power connection and it's aluminium base?

I have tested with a multimeter and it is open circuit, but I will be driving the LEDs at a much higher voltage than the multimeter is using to do the test.

The only safe way to know is to ask the manufacturer. – KalleMP Sep 06 '18 at 08:19 — KalleMP, Sep 06 '18 at 08:19

score 7 · Answer 1 · answered Oct 01 '16 at 21:01

7

Do COB LEDs usually need electrically insulating from the heatsink?

The LED chips inside the module are already isolated from the heatsink on the back. They must be because these modules contain many LEDs in series and that is why they need around 20 - 30 V to work. Each LED needs around 3 V so there must be many in series.

This can only work if all LEDs are isolated from the heatsink. So you can safely assume that the heatsink is already isolated from the LEDs . I would not make the voltage difference too large though but up to 50 V should generally be OK.

answered Oct 01 '16 at 21:01

Bimpelrekkie

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I will be driving in series, at 144v. There are examples in the design notes of driving 3 in series, but it does not say whether they are on the same heatsink. http://www.bridgelux.com/sites/default/files/resource_media/AN32-Vero-Series-Electrical-Drive-Considerations.pdf – John Spence Oct 02 '16 at 07:25
It can work if the heatsink is connected at one point, such as to the negative terminal. – user253751 Oct 02 '16 at 09:52
@immibis That is true but that would require an extra or different fabrication step: connecting the kathode of that LED chip to the heatsink. Since that doesn't bring anything it is simpler to make no connections to the heatsink at all. – Bimpelrekkie Oct 02 '16 at 10:03

score 3 · Answer 2 · answered Dec 21 '16 at 20:24

Working on a project now to connect several COB modules in series mounted on a single piece of aluminum channel. Finding on about 5 out of 20 that I tested there's a small current running between a connection lead (either anode or cathode) and the base. At 11 volts I'm getting 10-14 milliamps (enough to cause it to partially light up.) Due to the forward voltage threshold of the diodes, simply checking for resistance with my DMM reads open circuit - you have to check for current while running them at operating voltage.

To add some context, I bought several dozen of these 10 watt, 12v COB modules from a couple different ebay suppliers. Based on the price - $5-$10 for 10 pieces - I assume they're production seconds that failed to meet the manufacturer's QC requirements so I'm not completely surprised. Long story short, you may want to double check just to be sure.

score 1 · Accepted Answer · answered Oct 01 '16 at 20:57

Although I suspect they don't want you to zap the chip centre with 1kV, I am sure the thermal seat can withstand at least 1kV isolation.

Yes, electrically insulated heatsink surface is standard.

It claims to be somewhat ESD protected but it is not clear to what levels, so avoid large negative voltage and negative discharges to +.

Here's another thermal reference http://www.bridgelux.com/sites/default/files/resource_media/AN31-Handling-and-Assembly-of-Vero-LED-modules.pdf

Do COB LEDs usually need electrically insulating from the heatsink?

3 Answers3