Need help understanding DALI circuit and 220 VAC protection
Q1,Q3,R2,3,4,5 form a constant current regulator to limit the current current thru U1, D2 to something survivable, note that Q3 will dissipate considerable power when the mains fuckup fairy comes calling. 

D2,C2 produce a fixed low voltage rail to power the mosfet gate circuit, and I would assume that the firmware is written to NOT activate the transmitter if it is not seeing valid DALI (If you don't turn that mosfet on it will stand off 380 odd volts quite easily). 

I would guess that R1 is either a fusable resistor, a PTC or a straight up fuse.