In traditional designs, the highest cost of the circuitry is the part that provides 3.3 V to the fan speed controller. What we chose to do instead is to derive the 3.3 V directly from the 110 V AC ...

Pre-regulators at the input of power supplies minimize losses. This version uses optical feedback from an LED and light-dependent resistor instead of the more common optically isolated TRIACs. Fig 1.