Hi,
Your circuit has no voltage feedback so it cannot sense the output voltage and control it to a known value. I do not think that you have selected the best IC for a buck regulator circuit and you are certaintly not using that device correctly as you have drawn it.
I am not quite sure what you want your circuit to do, is it meant to produce a fixed or variable voltage output, you have not drawn the output voltage on your diagram, this is important to know, as is the load current required?
The TI UC3874 would be a better choice I think.
**broken link removed**
This datasheet has a suggested circuit to use. The inductor must be the correct value for these regulators to work, these are usually wound specially for your circuit, this is not difficult but switching regulators in general can be quite tricky to design and keep stable. Please tell me what you want your circuit to do and I will try to help you a bit more.
regards
Bob.