A comparator is an easy and reliable solution, if not minimalist, and you could do it with a transistor and some discretes also, though it would depend more on the details of your input signal...
But, your description is terribly confusing, and to me it sounds suspiciously like you're shorting your supply rail like justDIY said. Either that, or there's something you're leaving out. You should draw a diagram, because from your description I cannot picture what you are talking about.