How do I convert 12vdc to 1.5vdc for flashing mini-lights on my HO Scale Railroad system? The flasher will drive 2 alternately flashing bulbs (1.5 volts each) The maximum output of flasher is 100mA @ 12vdc.
Although an LDO or standard regulator can be used, the large voltage difference between input and output will result in significant power dissipation that is purely wasted:
100mA*(12.0-1.5) = 1W
That's a full watt that doesn't do anything but turn to heat (and you need to deal with properly dissipating it).
A DC/DC buck converter will give you what you want. For a ready made solution, Sparkfun has a breakout board for a DC/DC converter that will do what you need.
As suggested by Gustavo, buck regulator is the way to go.
Linear regulators are easier to build (less components) but lot of energy is wasted as heat. Linear regulators can offer cleaner supply (low ripple) if your application demands it.
Switching regulators reduce the wasted energy as compared to linear regulators.
Here is on such switching regulator from ebay the output is variable: