An attempt at building the cheapest mains voltage emergency light unit possible using the least circuitry. Full concept, design, PCB, etch, populate and test. Only issue with the design was a slight problem with the chosen Zener leaking too much current. That was fixed by using a lower power Zener with a low Zener-current.
The fully charged unit runs for about 10 hours at gradually reducing intensity and can easily light a room enough for navigation.
This project is quite dodgy because it's entirely referenced to the mains and an open circuit zener could result in serious lithium cell overcharging, even with protection circuitry (it's not rated for high voltages). The whole thing would have to be mounted in an insulated case including the LED.
The final circuit just had two component changes. The Zener was replaced with a lower power one with a lower Zener current of just 5mA and the X2 capacitor was replaced with a 220nF one for a higher charge current. For 120V use you would just need to change the X2 capacitor for a 330nF or 470nF one rated for 250V.
If you enjoy these videos you can help support the channel with a dollar for coffee, cookies and random gadgets for disassembly at:-
www.bigclive.com/coffee.htm
This also keeps the channel independent of KZfaq's advertising algorithms allowing it to be a bit more dangerous and naughty.