Can anybody tell me how this can possibly work? I need a super simple constant current supply from a rectified AC line. I came across this circuit in patent number 7,508,240. (http://www.google.com/patents/US7508240) I have no need for a zero crossing detector, as in the patent, but I do need a constant current source. How can simply putting a zener in parallel with the LED of an optocoupler work at this voltage level? I would figure the LED and zener would blow up if hooked to 1/2 wave pulsed 240VDC input. If this does work, is there any way to get some idea of what kind of zener and at what voltage? Is there any way to make this circuit provide about 15ma from the rectified line voltage? Thanks everyone.