Using 100 amp mopar alternator to charge batteries out of a vehicle

An adjustable regulator still works in the same "on" - "off" mode, however the voltage setpoint is adjustable. The voltage setpoint is always analog, the comparator determines when output is above or below setpoint, plus or minus a small voltage, about 0.1V, that serves as hysteresis. The hysteresis is a small window, where switching stops because voltage is in acceptable range.

A temperature thermostat is an "on"-"off" controller. It works the same way as a voltage regulator. If the room is cooler than the setting, then the furnace is "on", when the temperature increases, and reaches setpoint the furnace turns "off". The amount of time the furnace runs, depends on size of house, conditions outside, thermal losses, furnace size. The action of a voltage regulator is much faster...

When a transistor is "on" the losses are low, when "off" the current flow is zero. There are losses in the transition, but minimal, if the transistor, fits the application. The value of the hysteresis, impacts the switching interval. If the hysteresis is too small, then the transistor would operate in the active mode, similar to adjustable rheostat, that is horribly inefficient, as power is wasted as heat, and is dissipated by transistor. It is similar to furnace is always on, opening doors and windows to regulate heat. The heat loss is a huge drop in efficiency.