SDG #201 Exploring AC LED driver failure modes

Mains powered LED lighting has become one of the most common sources of electronic failure in the home, and this episode examines why. Rather than reviewing a single product, the focus is on the driver circuitry behind the LEDs, the part that almost always fails first, and on the specific mechanisms that cause it to fail.

Several recurring themes emerge. Electrolytic capacitors running hot inside sealed plastic bulb enclosures lose capacitance and rise in ESR, which shifts the operating point of the driver and can push current through the LEDs beyond their design limits. Capacitive dropper supplies, popular because they cost almost nothing, are particularly unforgiving: as the X rated capacitor drifts down in value the output collapses, and when a series element fails short the LED string receives far more energy than it should. Series filament strings and series wired emitters compound the problem, since one open die can take down the whole lamp or, worse, arc.

For anyone buying or specifying LED lighting, the practical conclusions are more useful than any single specification sheet. Thermal design matters more than the claimed lumen figure, drivers with proper constant current regulation outlast dropper based designs, and non-isolated topologies carry genuine safety implications for anyone opening a fitting. The discussion also serves as a primer for repair, since knowing the likely failure mode narrows fault finding to a handful of components, and it explains why a lamp rated for tens of thousands of hours can fail within a year.