Models / Electronics

LED Bulb

9 W E27 lamp, cut away to show its driver. Build it part by part in 3 stages, and learn what every one of its 11 parts does.

Parts, stage by stage

Insulator: Black glass or heat-proof plastic that keeps the live foot contact and the neutral screw shell apart, with the full mains voltage between them.
Foot contact: The brass tip is the live connection, soldered to the driver’s wire. It sits deep in the holder, where fingers cannot reach it.
E27 screw shell: The E27 Edison screw: 27 mm across, and the neutral connection as well as the fixing. Its rolled thread pulls the foot contact firmly onto the holder’s spring.
Body: Heat-resistant plastic that keeps fingers away from the mains electronics inside. Its label says 9 W and 806 lumens: as bright as an old 60 W bulb.

Driver board: Turns 230 V alternating current into the steady, low-voltage direct current LEDs need. A rectifier makes DC, and a controller chip switches it thousands of times a second to hold the current steady.
Smoothing capacitor: A small reservoir of charge that fills the gaps between mains peaks, so the light does not flicker. Heat slowly dries it out, so it is usually the first part to fail.
Inductor: Copper wire on a ferrite core. It stores energy each time the chip switches on and releases it when it switches off, stepping the voltage down with very little waste.

Heat sink: An aluminium cup that carries the LEDs’ heat out to the body. Cool LEDs stay bright and last for years.
LED board: A metal-core circuit board: aluminium under copper tracks and white, reflective paint. The tracks join the LEDs in series, so the same current flows through each.
LED chips: Twelve tiny blue LEDs under a yellow phosphor; the blue and yellow together look white. The blue LED won the 2014 Nobel Prize in Physics.
Diffuser dome: Frosted polycarbonate that scatters twelve bright points into one even glow, and keeps fingers off the live parts inside.