One of my LED bulbs failed yesterday so I decided to reverse engineer it, pretty much the way bigclivedotcom would himself do.
The PCB within my bulb is as per below:
It looks like one of the LEDs failed (marked with a circle around it and an F nearby). Although the PCB provides pads for heat dissipation, I think the choice of materials is pretty poor and heat is eventually guaranteed to destroy one of the LEDs.
Here’s the back side:
The burning is quite evident in the above image. In fact, the PCB looks quite cheap and thin: there’s no aluminium substrate for heat dissipation. Although aluminium helps with heat dissipation, it makes soldering a lot harder than on common PCBs as it is very effective at absorbing the heat from a soldering iron’s tip. So it looks like it might be a manufacturing trade-off.
Finally, here’s a scribble of the circuit in use by this LED bulb:
As some of you might have guessed, this is a capacitive dropper circuit with four diodes to implement a bridge rectifier.
The bleeder resistor is used to discharge the capacitor on the left of the circuit when the bulb is taken out and avoid a tiny electric shock when its contacts are touched.