3). Input Power stage
The controller MCU (Motor Control Unit) and other parts of the board needs a fixed regulated voltage to run from. The controllers I have looked at seem to have a +12 volt and a + 5 volt line to drive these devices and external devices, such as throttle, PAS, Cruise, etc. These voltages need to be derived from the input voltage, and obviously a low voltage controller has to drop less voltage to reach 5 v than does the input stage of a 150v controller.
I am sure there is as many differing designs as there are electronics engineers and board design, but so far I have come across three basic different ones
1) Switched Mode Power supply ...built on to the board, wide ranging input voltages.
2). Initial voltage drop with Comparator and NPN PNP transistor switching. Dropping to 20 volts or so, feeding power dropper resistors, and zener to give 15 volts, this feeding a regulator outputting 5 volts
3). LM317 style regulator.. also with power resistors to drop voltage.
Designs 2 and 3 are very similar, but I am not an EE, so can't do better than warn you there are differences.
The real point of this Wiki Entry is to make you aware of the different input designs, and the fact that your controller could have one of these or possibly others. So any advice you get to do this or that mod to change input voltage may not be compatible with the controller you have