Patent ID: 7511972

Claim:
A transformer-coupled DC-DC converter comprising: a voltage input terminal for connection to a main power supply for supplying power to the converter at a first supply voltage; a primary winding of a transformer; a first switch controlled to intermittently conduct a current from the voltage input terminal through the primary winding, the primary winding generating a ramping current when the first switch is turned on and generating a momentary voltage pulse upon the first switch turning off; a secondary winding of the transformer supplying a current to an output circuit for providing a DC output voltage of the converter; and a voltage regulator receiving at a regulator input terminal an input voltage generated from the momentary voltage pulse, the regulator comprising a second switch for intermittently coupling the regulator input terminal to an output filter of the regulator, the output filter of the regulator being coupled to the voltage input terminal of the converter, the regulator controlling the input voltage to be at a regulated voltage, such that at least some of the energy in the voltage pulse is returned to the voltage input terminal and a voltage across the first switch is limited by the input voltage of the regulator, wherein at least some of the energy in the voltage pulse is returned to the voltage input terminal upon each switching cycle of the first switch while the input voltage into the regulator is being regulated.