Some of the replies here seem a little harsh. Certainly there's a misunderstanding on how zeners work, but honestly I've been there too. Many of the introductory tutorials sort of paint a zener as a cheap and easy regulator, with very little mention of gradual knees and current dependence. I had a sense that nothing in life is ever that simple, so there must be more to it. Turns out there is. Between "This is what a zener diode looks like" and the graphs in the latter pages of a datasheet, there's quite a void. The information is there, you just have to know to look for it.So, it seems to me if you're going to take the time to post a reply criticizing someone's lack of understanding, at least take the time to suggest a correct approach. If you can't be bothered, just move on. Thanks to everyone here that takes that extra step, though. I for one appreciate it greatly.
There is this tutorial by Grumpy Mike:http://www.thebox.myzen.co.uk/Tutorial/Protection.htmlI don't know if his previous comments detract from this?