Zero voltage switching power converters

A power converter comprising:

• a transformer including a primary winding, a secondary winding, and a third winding, the primary winding coupled to an input port for receiving a source of power and the secondary winding coupled to an output port for providing output power to a load;
• a primary switch means coupled in series with said primary winding, said primary switch means when closed causing a first portion of energy from said power source to be coupled through said transformer to said output load port by means of said secondary winding and causing a second portion of said energy to be stored in the transformer in the form of magnetic flux having a first direction through the windings of said transformer;
• a flux reversal means for reversing the direction of said magnetic flux built up in said transformer when said primary switch means is opened, said flux reversal means comprising a series combination of a first switch means coupled in series with said third winding, said series combination coupled to a source of voltage such that a reversing voltage may be applied to said transformer windings when said first switch means is closed, said reversing voltage being opposite in sign to the voltage applied to said windings when said primary switch means is closed, said first switch means being caused to close substantially when the primary switch means opens to apply said reversing voltage and being caused to open substantially when the primary switch means closes, said reversing voltage operating to reverse the direction of the flux through said transformer built up during the preceding closed time of said primary switch means;
• a secondary switch means coupled in series with said secondary winding of said transformer;
• and
• a switch control means for operating said secondary switch means in relation to the operation of said primary switch means and said flux reversal means, said switch control means opening said secondary switch means substantially when said primary switch means opens and closing said secondary switch means substantially when said primary switch means closes such that substantially no current is conducted by said secondary winding during a predetermined interval prior to when said primary switch means is closed, said secondary switch means and said flux reversal means operating to substantially reduce the voltage across said primary switch means when said primary switch means next is caused to close.

A power converter comprising:

• an input port for receiving a first source of power;
• a second source of power;
• a transformer including a primary winding and a secondary winding, said primary winding including a first terminal and a second terminal, said second terminal being coupled to said second source of power, said secondary winding being coupled to an output port for providing output power to a load;
• a primary switch means coupled to said first terminal of said primary winding, said primary switch means when closed causing a first portion of energy from said second power source to be coupled through said transformer to said output port by means of said secondary winding and causing a second portion of said energy to be stored in the transformer in the form of magnetic flux having a first direction through the windings of said transformer;
• a flux reversal means for reversing the direction of said magnetic flux built up in the transformer when said primary switch means is opened, said flux reversal means comprising a first switch means having a first terminal coupled to said input port and a second terminal coupled to said first terminal of said primary winding, said first switch means applying a reversing voltage to said transformer windings when said first switch means is closed, said reversing voltage being opposite in sign to the voltage applied to said windings when said primary switch means is closed, said first switch means being caused to close substantially when the primary switch means opens to apply said reversing voltage and being caused to open substantially when the primary switch means closes, said reversing voltage operating to reverse the direction of the flux through said transformer built up during the preceding closed time of said primary switch means;
• a secondary switch means coupled in series with said secondary winding of said transformer;
• and
• a switch control means for operating said secondary switch means in relation to the operation of said primary switch means and said flux reversal means, said switch control means opening said secondary switch means substantially when said primary switch means opens and closing said secondary switch means substantially when said primary switch means closes such that substantially no current is conducted by said secondary winding during a predetermined interval prior to when said primary switch means is closed, said secondary switch means and said flux reversal means operating to substantially reduce the voltage across said primary switch means when said primary switch means next is caused to close.

A power converter comprising:

• an input port for receiving a source of power;
• a transformer including a primary winding and a secondary winding, said primary winding including a first terminal and a second terminal, said secondary winding being coupled to an output port for providing output power to a load;
• a first primary switch, a second primary switch, a first switch means, and a second switch means, said first primary switch being coupled to said first terminal of said primary winding and said second primary switch being coupled to said second terminal of said primary winding, said first and second primary switch being coupled to said input port such that when closed said first and second primary switches cause a first portion of energy from said power source to be coupled through said transformer to said output load port by means of said secondary winding and cause a second portion of said energy to be stored in the transformer in the form of magnetic flux having a first direction through the windings of said transformer, said first switch means being coupled to said first terminal of said primary winding and said second switch means being coupled to said second terminal of said primary winding, said first and second switch means coupled to input port such that said first and second switch means apply a reversing voltage to said transformer windings when said first and second switch means are closed, said reversing voltage being opposite in sign to the voltage applied to said windings when said first and second primary switches are closed;
• a secondary switch means coupled in series with said secondary winding of said transformer;
• means for closing each of said first and second switch means substantially when said first and second primary switches open and opening each of said first and second switch means prior to when said first and second primary switches close, said first and second switch means coupling a reversing voltage to said transformer windings to reverse the direction of the flux through said transformer built up during the preceding closed time of said first and second primary switches;
• means for operating said secondary switch means in relation to the operation of said first primary switch, said second primary switch, said first switch means, and said second switch means, said means opening said secondary switch means substantially when said first and second primary switches open and closing said secondary switch means substantially when said first and second primary switches close such that substantially no current is conducted by said secondary winding during a predetermined interval prior to when said first and second primary switches are closed, said secondary switch means, said first switch means, and said second switch means operating to substantially reduce the voltage across said first and second primary switches when said first and second primary switches next are caused to close.