Dear all:
I'm designing the power supply end of a new gizmo (my first power supply in ages), and I'd like some advice on the protection network on the DC power input. (I've just had a nice iRiver MP3 player blown up by a failed no-name Chinese wall wart, so power-brick fault protection is on my mind.)
Back in the day, I'd just have used a crowbar SCR and a PTC thermistor, but I'm worried that doing that might make a failed wall wart catch fire. Sooo, I'm looking instead at PTCs and transient-protection zeners.
If the PS goes really bananas, the PTC will switch fast enough that the zener won't desolder itself from the board, but if the PS just goes out of spec (e.g. 24V for a 12V brick), the zener winds up dissipating a lot of power for a long time (seconds) before the PTC switches.
Soooo....what does the assembled multitude use for DC power input protection?
Cheers
Phil Hobbs