Maxflex3

[georges80]

Using the built in temperature monitoring of bFlex, nFlex or maxFlex (and now d2Flex) to limit the LED temperature is certainly NOT a bad idea. The primary intention to provide temperature limiting of the driver was specifically to keep the entire "system" within reasonable limits.

nFlex and bFlex are very different thermally than maxFlex due to the typical usage of the drivers. With maxFlex being a boost, many folk are tempted to drive 5 or 6 LEDs and at full 1200mA output and thus the total power through the driver is much higher than the typical 3 LED configuration (at 1000mA) of nFlex and bFlex. The efficiency of maxFlex can also be several percent less than nFlex/bFlex due to it being a boost converter and thus having much higher input current (and thus losses).

So, overall maxFlex will typically be running hotter and cooling/temperature control is more critical. The temperature sensing is performed within the uController (calibrated prior to shipping) and there can be a thermal lag between the switcher IC getting toasty and the uController sensing it. In some rare circumstances (higher power situations) this can cause the switcher to overheat before the uController can back down the current since it takes time for the heat to spread across the PCB and warm up the uController. In these rare situations using thermal epoxy on the switcher top side (inductor side) and letting a bit more ooze from the thermal pad/heatsink attach to the uController (the chip next to the golden thermal pad) will help with the heat coupling.

cheers,
george.

 

[georges80]

Ok, so I just got notice from my assembly house that they shipped a decent sized batch of maxflex3 drivers this morning, which means I'll have them in hand tomorrow.

So, finally the drought will be over!

cheers,
george.

 

[dnlwthrn]

Order placed.... (gets excited)

Now I just need to get my order from Cutter to show up... Could be lots of lights being built this winter!

 

[Zero_Enigma]

Arctic Alumina epoxy is fine - though rather expensive to use a lot. I'd recommend using a combination of heatsink attached to the thermal pad at the bottom of the PCB (the rectangular gold area) AND AA epoxy (or similar quality thermal epoxy that is essentially non-conductive & non-capacitive) to pot the top of the board (the switcher IC area) to another heatsink attachment. Potting on its own isn't enough - it needs to be used as a path to a heatsink that can move heat off the board and radiate it away.

The potting is required at the higher power levels - say above 1.5W - though it all depends on ambient temperature. If you have maxFlex inside the LED housing and it is 'cooking' then you will have trouble.

Turning on the thermal protection in the menu system would be a good idea and backup plan to protect the driver.

cheers,
george.

I am a visual learner so photos or side by side hands on is how I learn best. Can you provide some photos (more then one please of different angles) if the 'potting' of the IC chip and the thermopad thing? Thanks in advance.

 

[hootsmon]

I have no experience with thermal-potting resin. However I'm planning to give it a try. Here's a pic (that I posted earlier on MTBR), which shows how I'm proposing to do the first light. Later I'd do a Znomit-style light in a similar manner (if it works of course).

Basically the plan is to wire up the whole circuit and test it on the bench first. Then once I'm happy it's all working just I'd pour the potting-goop into the sawn-off Berocca can, and leave it to set. Then test it one more time, before sliding the assembly into the housing, and AA'ing them into place. Or maybe I should use Artic-silver grease, so it can be easily disassembled for troubleshooting? Anyway, here's the pic....

Any thoughts?

 

[hootsmon]

Since my previous post, I've started reading-up on thermal-potting resin, and the more I read the less I liked the sound of it. Then I re-read George's post #13, and now I grok what he's saying about Arctic Alumina being sufficient if you provide an adequate heatsink. Consequently, I've gone right off the potting-resin idea that was shown in the pic. Instead, I'll just just do this:

• AA bond a small Alu pad, covering the maxFlex's heatsink spot
• Apply a generous squidge of AA, covering both switcher IC & the Alu pad
• Stick the lot directly onto a heatsink mounted on the back-cap

Sounds simpler than the potting idea