I have a requirement for a circuit that will allow an opto coupler led to be driven from 10v-320v ac or dc. The application is a plc like controller (using an 8051 derivative of course!!) where an input in the abovementioned range will work. It is a digital input 0v = off, >10vac/dc is on.

It is the wide voltage range that provides the conundrum here.

I've done a search and there's some devices for the high power leds that do exactly this by using switch mode techniques. I'm hoping for a discrete component solution.

I seem to recall a circuit once that did what I require but I can no longer remember where I saw it. It seems like a simple problem, but my poor brain cannot provide a solution. So I'm hoping someone out there can suggest something or point me towards a link.