EEVblog 1453 - Elgato Key Light Teardown

[EEVblog]

Teardown of the Elgato Key Light
https://amzn.to/3oqObEW

[Tom45]

Let the light warm up and then do some temperature measurements. It would be interesting to see if it really needs better thermal flow to the frame or not.

[Fungus]

I was sure Dave had a thermal camera somewhere...

[jancumps]

The controller/wifi part is an off-the shelf module from Dexatek.

[thm_w]

If you buy just one its not cheap, $300/ea (CAD)! Dave gave the price of two units.

The controller/wifi part is an off-the shelf module from Dexatek.

He did post the datasheet, looks like it WIFI only, no BT (DK-9169).
I don't see any public pricing of the module, I would have thought <$2, although the only rtl8711am modules I see on Ali are in the $4 range.

[Faranight]

Hi, Dave! A couple of questions.

- Why are they using a 16 channel PWM driver (PCA9635) to drive a single LED strip?
There seem to be 4 lines (4 pairs of wires) running to the strip and I've seen only 4 SOT-23 mosfets on the board.
So even if they're using 4 channels that way, that still leaves 12 channels unused. How does that work?
P.S. the PCA9635 datasheet is wrong - it says 16-bit LED driver, but it's actually 16 channel, 8-bit LED driver.

- What PWM frequency are they running the strips at?
Datasheet says the IC works at 97 kHz.
Isn't this frequency gonna cause EMI up to a few MHz down the external wires that feed power to the LED strips?

[thm_w]

Hi, Dave! A couple of questions.

- Why are they using a 16 channel PWM driver (PCA9635) to drive a single LED strip?
There seem to be 4 lines (4 pairs of wires) running to the strip and I've seen only 4 SOT-23 mosfets on the board.
So even if they're using 4 channels that way, that still leaves 12 channels unused. How does that work?
P.S. the PCA9635 datasheet is wrong - it says 16-bit LED driver, but it's actually 16 channel, 8-bit LED driver.

- What PWM frequency are they running the strips at?
Datasheet says the IC works at 97 kHz.
Isn't this frequency gonna cause EMI up to a few MHz down the external wires that feed power to the LED strips?

There is no problem with using 4 channels of a 16 channel chip, just means they've left some unused. For the cost of this product, the PCA9635 is relatively cheap, and means they don't have to deal with PWM on the microcontroller, it can setup the PWM then go off to do other things and the PWM will always be stable. Also another micro could be swapped in, and it will work as long as it supports i2c.

As for EMI, they have the big resistors, and are soft switching the gates with 1k resistors. Should be ok.