Quick question: If I stick a zener at the adjust pin of a 3 terminal linear voltage regulator, the allowable maximum input voltage will also increase by the breakdown voltage of the zener used... right? I'm not worried about noise and bad regulation due to the zener. The regulators I'm considering are the AMS1117-5.0 and maybe the LM7805 (although the 7805 will probably not pose a problem as the input limit is fairly high).
I need to get 120mA @ ~12V and only have the 5V regulators on hand (and a bunch of zeners). Input ripple varies from 13-16V. This is for running a 12V fan. Apparently, vregs are cheaper than transistors, and board space is limited.