My LED shelf whined, and got louder when dimmed. So I built a silent replacement.
The shelf is a 24 V tunable white/orange strip, with two anti-parallel strings, driven by an off the shelf controller. At full brightness it made a high pitched wine. Dimmed to a usable level, it got even worse!
Scoping the original controller’s output showed it drives the LEDs with a 2 kHz H-bridge waveform, and dimming inserts 0 V dwell that pumps energy into the harmonics right where your ear is most sensitive. A mic 5 cm away confirmed it, a harmonic comb spaced at 1999 Hz, with the 4 kHz member 16 dB louder when dimmed.
The replacement is an STM32 driving a three level H-bridge at 25 kHz through a proper gate driver, BLE control, on a 4 layer board sized to drop into the original enclosure.
Every harmonic now lands above the audible band. Current draw came out the same as the original, so the silence was basically free. It also remembers brightness and colour through power cuts, the F303 has no EEPROM so state gets debounced into a flash page.
Full writeup with the scope captures, audio FFTs and design files: https://github.com/AShadyPCB/led-shelf-controller
