SDG #325 Designing a WLED RGBW light with only one LED driver

Most WLED-based RGBW fixtures throw a separate constant current driver at every colour channel, which multiplies cost, board area and inductor count by four. This design walks through an alternative: one buck LED driver feeding all four channels, with per-channel switching handling which string actually sees current at any given moment. It is a neat cost reduction trick, but it comes with real engineering trade-offs that are worth understanding before copying the idea.

The key issue is what happens to a current-mode buck regulator when its load is switched out from under it. Forward voltages differ between red, green, blue and white dies, so the driver has to settle to a new operating point every time channels change, and PWM dimming means that can happen thousands of times a second. LTspice modelling is used here to look at the current overshoot and settling behaviour, which is exactly the kind of homework that separates a design that works on the bench from one that flickers or stresses the LEDs.

The AL8843 is chosen as the driver, a hysteretic buck device that is cheap, widely available and tolerant of the fast load changes this topology creates. From there the video covers the full schematic, including the ESP-based WLED controller side, channel switching and current setting, then moves into PCB layout and sending the board off for fabrication.

For anyone building custom lighting rather than buying off-the-shelf strips, the useful takeaway is the reasoning: where the single-driver approach saves money, and where the switching transients set the limits on what you can get away with.