By using a capacitor to capture the huge voltage diff, the 50+v is stored and discharged in a small cap. I rectify this to get a charge when this cap is discharging as well. A low pass filter is used at the current control to smoothen the current ripple. You do lose power with this circuit in theory, but not to excessive heat from stepping down. (A transformer would probably conserve this energy, as it shouldn't be destroyed. I dunno)
