Saturday, January 4, 2020

Cheap Fix For BMW X3 F25 Tail Lights / Rear Lights

I designed switch mode LED driver board for BMW X3's tail lights. The second generation X3, the F25 in specific.

This project video and blog post was sponsored by PCBWay.
$5 for 10 PCBs plus shipping, 1-2 layers, max 100x100mm. 24h build time.
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There are plenty of reports on BMW X3's LED rear lights going dark, one by one. Official replacement parts costs quite a lot, compared to the price of blown out bulb in older cars.
The problem that causes those tail lights to go out is the linear LED driver inside the tail light. That driver is wasting most of it's input power as heat and that causes the solder joints to fail, stopping it from working.

Personally I don't own said BMW X3, but friend of mine does. Last summer he asked if I'd be able to repair his BMW X3 F25's tail lights, by redoing some failed solder joints on the original LED driver PCB. Sure thing I was able to do that and then do one better and design more efficient circuit to replace the original ones.

The design of my improved LED-drivers has higher efficiency, meaning they produce less heat. I also made sure that the installation is simple, by using the exact same connector as on the original PCB.

I searched for cost effective solution and ended up designing my solution around SD42522 IC, which helps keeping BOM cost low.

This schematic is based on the schematic from the controller's datasheet (PDF, opens in new window/tab). You should check the datasheet and adjust the values to match your needs, if you are using this IC.

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