Patent ID: 7199562

Claim:
A switch mode power supply, comprising: a source of a periodic input supply voltage; a filter capacitor; a power, switching semiconductor coupled to said source and to said capacitor for generating periodic rectified supply current pulse in said semiconductor having a first transition in a first direction and a second transition at an opposite direction at a frequency related to that of said input supply voltage to develop an output supply voltage in said capacitor, the power, switching semiconductor comprising a series pass transistor coupled in series with a rectifier for preventing said capacitor from discharging via said transistor, outside said rectified supply current pulse; a source of a first switch control signal for conditioning said semiconductor to conduction prior to said first transition in a manner to provide for zero voltage switching in said semiconductor, during said first transition; and a comparator responsive to a signal indicative of said output supply voltage and to a signal at a reference level for generating a second switch control signal for said semiconductor to produce said second transition of said current pulse that is modulated, in accordance with a difference between said output supply voltage and said reference level signal, said comparator having a positive feedback signal path that provides hysteresis with respect to said output supply voltage.