I was bored one day so I took apart an old (as in no longer needed, late 2013) phone charger.
Everything looks well designed except for the spark gap between neutral/live and the low-voltage side. I'd understand if it was placed between live and neutral, but this one makes it look like you could get zapped if you're holding the phone while it's charging and a massive voltage spike occurs.
What good is it doing where it's placed?
The black thing that sticks out on the top left side is two wires for 5V DC out.
AC in is at the bottom fork-looking pads.
Best Answer
It's simply there to prevent the secondary side from building up arbitrarily large static charges, nothing else.
Common-mode primary-side surges large enough to jump the gap are vanishingly rare — and if one occurs, you've got bigger problems anyway. Differential-mode surges are probably handled by other components, such as a MOV, TVS or gas discharge tube.