Kai,

I've had cases where these pcb mounted transformers have removed themselves from the pcb. Many of the larger ones have a tapped hole(s) so you can put a screw thru the pcb to hold them. As for the Block transformer you have suggested, I haven't perused the data on them. Nevertheless I am wary of high mass items being held on via pcb pins!

I had a brief look at the pc900v specs which had a nice graph detailing the transition points vs input current, at 5v it was about 1mA. I'd better look at the derating vs temperature! I was going to run it at about 1.4mA to give some headroom.

Your comments regarding the temp drift of the CC source and voltage spikes are noted. I have to put a zener or two in there - one for a low voltage snap off, the other as a reference for the CC transistor (or mosfet). A bit of R and C around the opto led should protect it against a high dVdT transient that's too fast for the constant current source to respond to. The MOV should pick out most of the high voltage spikes (> 320v) as they are quite fast at responding.