Resonant forward converter

A dual resonant forward converter for converting voltage from an input dc voltage source to an output dc voltage for delivery to a load comprising:

• two transformers each having a primary and secondary winding wound about a core element in a manner in which the polarities of the windings are matched, each transformer having a magnetizing inductor connected in parallel across one of its windings to provide a respective resonant ring independent of the load, each magnetizing inductor being naturally supplied by a magnetizing inductance of the respective transformer;
• two switching means, one connected in series with the primary winding of one transformer and the input dc voltage source for alternately switching current on and off at a rapid rate through a first series circuit, the second switching means connected in series with the primary winding of the second transformer and the input dc voltage source for alternately switching current on and off at a rapid rate through a second series circuit, each switching means causing, when it is turned off, a ring between the respective magnetizing inductor of the transformer to which the switching means is connected and a first capacitor means coupled in parallel with the switching means;
• said first series circuit comprising the input dc voltage source, the primary winding of the one transformer, and the one switching means in parallel with the respective first capacitor means;
• said second series circuit comprising the input dc voltage source, the primary winding of the second transformer, and the second switching means in parallel with its respective first capacitor means;
• a third series circuit comprising the secondary winding of the one transformer in series with a first unidirectional conducting means, a common node, a first parallel output capacitor and said load, said first unidirectional conducting means having a second capacitor means coupled in parallel therewith such that the first unidirectional conducting means acts in unison with the one switching means, both being turned on and off at about the same time, and the first capacitor means of the first series circuit acting in parallel with the second capacitor means during the respective ring;
• and
• a fourth series circuit comprising the secondary winding of the second transformer in series with a second unidirectional conducting means, the common node, the first parallel output capacitor, and said load, said second unidirectional conducting means having a third capacitor means coupled in parallel therewith such that the second unidirectional means acts in unison with the second switching means, both being turned on and off at about the same time, the first capacitor means of the second series circuit acting in parallel with the third capacitor means during the respective ring.

A method of converting a dc voltage source to an output dc voltage for delivery to a load, the steps comprising:

• switching current alternately on and off at a rapid rate through a series circuit of a resonant forward converter having a transformer with a primary and secondary winding wound about a core element with matching polarity, a first inductor connected in parallel across one winding of the transformer to provide a resonant ring independent of the load;
• a unilateral conducting device connected in series between the secondary winding and the load, the series circuit including the voltage source and the primary winding of the transformer;
• and
• switching the unilateral conducting device alternately on and off respectively at the same time as the the switching on and off of the current through the series circuit.

A method of converting a dc voltage source to an output dc voltage for delivery to a load, the steps comprising:

• switching current alternately on and off at a rapid rate through two series circuits of a resonant forward converter having two transformers each with a primary and secondary winding wound about a core element with matching polarity, two first inductors one connected in parallel across one winding of one transformer to provide a resonant ring independent of the load, and the second connected in parallel across the winding of the second transformer to provide a resonant ring independent of the load;
• two unilateral conducting devices, one connected in series between the secondary winding of the one transformer and the load, the other connected in series between the secondary winding of the second transformer and the load, the two series circuits each including the voltage source and the primary winding of the respective transformer;
• and
• switching two unilateral conducting devices alternately on and off respectively at the same time as the switching on and off of the current through the two series circuits.

A circuit for pre-regulating input voltage to a converter having a transformer with a primary winding, the circuit comprising:

• a main bus leading to the converter;
• an inductor connected in series with a first diode, the first diode connected to the main bus;
• a controllable switch connected in series with the inductor and a midpoint of the bus, the midpoint formed by two capacitors;
• a unilateral conducting means connected in series with the midpoint and a tap on the primary winding of the transformer such that the input voltage may have a limited range while volage of the midpoint is controlled by the controllable switch and unilateral conducting means.

A circuit for pre-regulating input voltage from a source to a converter having a transformer with a primary winding, the circuit comprising:

• a main bus leading to the converter;
• a first element connected in series with the source and a second element, the second element connected to the main bus, a node being formed where the first element and the second element connect;
• a third element connected between the node and a midpoint of the main bus, the midpoint formed by two capacitors placed in series;
• and
• a unilateral conducting means connected in series with the midpoint and a tap on the primary winding of the transformer such that the input voltage may have a limited range while voltage of the midpoint is controlled by one of the elements and the unilateral conducting means.

A dual resonant forward converter for converting voltage from an input dc voltage source to an output dc voltage for delivery to a load comprising:

• two transformers each having a primary and secondary winding wound about a core element in a manner in which the polarities of the windings are matched, each transformer having a magnetizing inductor connected in parallel across one of its windings to provide a respective resonant ring independent of the load, each magnetizing inductor being naturally supplied by a magnetizing inductance of the respective transformer;
• two switching means, one connected in series with the primary winding of one transformer and the input dc voltage source for alternately switching current on and off at a rapid rate through a first series circuit, the second switching means connected in series with the primary winding of the second transformer and the input dc voltage source for alternately switching current on and off at a rapid rate through a second series circuit, each switching means causing, when it is turned off, a ring between the respective magnetizing inductor of the transformer to which the switching means is connected and a first capacitor means coupled in parallel thereto with the switching means;
• said first series circuit comprising the input dc voltage source, the primary winding of the one transformer, and the one switching means in parallel with the respective first capacitor means;
• said second series circuit comprising the input dc voltage source, the primary winding of the second transformer, and the second switching means in parallel with its respective first capacitor means;
• a third series circuit comprising the secondary winding of the one transformer in series with a first synchronous rectifier, a common node, a first parallel output capacitor and said load, said first synchronous rectifier having a second capacitor means coupled in parallel therewith such that the first synchronous rectifier acts in unison with the one switching means, both being turned on and off at about the same time, and the first capacitor means of the first series circuit acting in parallel with the second capacitor means during the respective ring;
• a gate of the first synchronous rectifier cross coupling to the secondary winding of the second transformer;
• a fourth series circuit comprising the secondary winding of the second transformer in series with a second synchronous rectifier, the common node, the first parallel output capacitor, and said load, said second synchronous rectifier having a third capacitor means coupled in parallel therewith such that the second synchronous rectifier acts in unison with the second switching means, both being turned on and off at about the same time, the first capacitor means of the second series circuit acting in parallel with the third capacitor means during the respective ring;
• a gate of the the second synchronous rectifier cross coupling to the secondary winding of the one transformer, the first and second synchronous rectifiers providing a reduction in conduction losses;
• two leakage inductors, one connected in series with one of the windings of the one transformer, the second connected in series with one of the windings of the second transformer;
• and
• each leakage inductor being supplied by a leakage inductance of the respective transformer, the leakage inductance being negligibly small relative to the magnetizing inductance of the respective transformer such that the first and second synchronous rectifiers and the two switching means all have zero voltage switching transitions.

A dual resonant forward converter for converting voltage from an input dc voltage source to an output dc voltage for delivery to a load comprising:

• two transformers each having a primary and secondary winding wound about a core element in a manner in which the polarities of the windings are matched, each transformer having a magnetizing inductor connected in parallel across one of its windings to provide a respective resonant ring independent of the load, each magnetizing inductor being naturally supplied by a magnetizing inductance of the respective transformer;
• two switching means, one connected in series with the primary winding of one transformer and the input dc voltage source for alternately switching current on and off at a rapid rate through a first series circuit, the second switching means connected in series with the primary winding of the second transformer and the input dc voltage source for alternately switching current on and off at a rapid rate through a second series circuit, each switching means causing, when it is turned off, a ring between the respective magnetizing inductor of the transformer to which the switching means is connected and a first capacitor means coupled in parallel thereto with the switching means;
• said first series circuit comprising the input dc voltage source, the primary winding of the one transformer, and the one switching means in parallel with the respective first capacitor means;
• said second series circuit comprising the input dc voltage source, the primary winding of the second transformer, and the second switching means in parallel with its respective first capacitor means;
• a third series circuit comprising the secondary winding of the one transformer in series with a first unidirectional conducting means, a common node, a first parallel output capacitor and said load, said first unidirectional conducting means having a second capacitor means coupled in parallel therewith such that the first unidirectional conducting means acts in unison with the one switching means, both being turned on and off at about the same time, and the first capacitor means of the first series circuit acting in parallel with the second capacitor means during the respective ring;
• a fourth series circuit comprising the secondary winding of the second transformer in series with a second unidirectional conducting means, the common node, the first parallel output capacitor, and said load, said second unidirectional conducting means having a third capacitor means coupled in parallel therewith such that the second unidirectional means acts in unison with the second switching means, both being turned on and off at about the same time, the first capacitor means of the second series circuit acting in parallel with the third capacitor means during the respective ring;
• two leakage inductors, one connected in series with one of the windings of the one transformer, the second connected in series with one of the windings of the second transformer;
• each leakage inductor being supplied by a leakage inductance of the respective transformer, the leakage inductance being negligibly small relative to the magnetizing inductance of the respective transformer such that the first and second unidirectional conducting means and the two switching means all have zero voltage switching transitions;
• and
• circuit means for pre-regulating the voltage presented to the first and second series circuits.

A dual resonant forward converter for converting voltage from an input dc voltage source to an output dc voltage for delivery to a load comprising:

• two transformers each having a primary and secondary winding wound about a core element in a manner in which the polarities of the windings are matched, each transformer having a magnetizing inductor connected in parallel across one of its windings to provide a respective resonant ring independent of the load, each magnetizing inductor being naturally supplied by a magnetizing inductance of the respective transformer;
• two switching means, one connected in series with the primary winding of one transformer and the input dc voltage source for alternately switching current on and off at a rapid rate through a first series circuit, the second switching means connected in series with the primary winding of the second transformer and the input dc voltage source for alternately switching current on and off at a rapid rate through a second series circuit, each switching means causing, when it is turned off, a ring between the respective magnetizing inductor of the transformer to which the switching means is connected and a first capacitor means coupled in parallel thereto with the switching means;
• said first series circuit comprising the input dc voltage source, the primary winding of the one transformer, and the one switching means in parallel with the respective first capacitor means;
• said second series circuit comprising the input dc voltage source, the primary winding of the second transformer, and the second switching means in parallel with its respective first capacitor means;
• a third series circuit comprising the secondary winding of the one transformer in series with a first synchronous rectifier, a common node, a first parallel output capacitor and said load, said first synchronous rectifier having a second capacitor means coupled in parallel therewith such that the first synchronous rectifier acts in unison with the one switching means, both being turned on and off at about the same time, and the first capacitor means of the first series circuit acting in parallel with the second capacitor means during the respective ring;
• a gate of the first synchronous rectifier cross coupling to the secondary winding of the second transformer;
• a fourth series circuit comprising the secondary winding of the second transformer in series with a second synchronous rectifier, the common node, the first parallel output capacitor, and said load, said second synchronous rectifier having a third capacitor means coupled in parallel therewith such that the second synchronous rectifier acts in unison with the second switching means, both being turned on and off at about the same time, the first capacitor means of the second series circuit acting in parallel with the third capacitor means during the respective ring;
• and
• a gate of the second synchronous rectifier cross coupling to the secondary winding of the one transformer, the first and second synchronous rectifiers providing a reduction in conduction losses.

A dual resonant forward converter for converting voltage from an input dc voltage source to an output dc voltage for delivery to a load comprising:

• two transformers each having a primary and secondary winding wound about a core element in a manner in which the polarities of the windings are matched, each transformer having a magnetizing inductor connected in parallel across one of its windings to provide a respective resonant ring independent of the supplied by a magnetizing inductance of the respective transformer;
• two switching means, one connected in series with the primary winding of one transformer and the input dc voltage source for alternately switching current on and off at a rapid rate through a first series circuit, the second switching means connected in series with the primary winding of the second transformer and the input dc voltage source for alternately switching current on and off at a rapid rate through a second series circuit, each switching means causing, when it is turned off, a ring between the respective magnetizing inductor of the transformer to which the switching means is connected and a first capacitor means coupled in parallel thereto with the switching means;
• said first series circuit comprising the input dc voltage source, the primary winding of the one transformer, and the one switching means in parallel with the respective first capacitor means;
• said second series circuit comprising the input dc voltage source, the primary winding of the second transformer, and the second switching means in parallel with its respective first capacitor means;
• a third series circuit comprising the secondary winding of the one transformer in series with a first unidirectional conducting means, a common node, a first parallel output capacitor and said load, said first unidirectional conducting means having a second capacitor means coupled in parallel therewith such that the first unidirectional conducting means acts in unison with the one switching means, both being turned on and off at about the same time, and the first capacitor means of the first series circuit acting in parallel with the second capacitor means during the respective ring;
• a fourth series circuit comprising the secondary winding of the second transformer in series with a second unidirectional conducting means, the common node, the first parallel output capacitor, and said load, said second unidirectional conducting means having a third capacitor means coupled in parallel therewith such that the second unidirectional means acts in unison with the second switching means, both being turned on and off at about the same time, the first capacitor means of the second series circuit acting in parallel with the third capacitor means during the respective ring;
• and
• circuit means for pre-regulating the voltage presented to the first and second series circuits.

A resonant forward converter for converting voltage from an input dc voltage source to an output dc voltage for delivery to a load comprising:

• a transformer having a primary and secondary winding wound about a common core element in which the polarities of the windings are matched, said transformer having a magnetizing inductor connected in parallel across one of said windings to provide a resonant ring independent of the load, the magnetizing inductor being naturally supplied by a magnetizing inductance of the transformer;
• switching means connected in series with said primary winding and said input dc voltage source for alternately switching current on and off at a rapid rate through a first series circuit, said switching means causing, when it is turned off, a ring between the magnetizing inductor and a first capacitor means coupled in parallel with the switching means;
• said first series circuit comprising the input dc voltage source, the primary winding of said transformer and the switching means in parallel with said first capacitor means;
• a second series circuit comprising said secondary winding of the transformer in series with a first unilateral conducting means, a parallel output capacitor and said load, said first unilateral conducting means having a second capacitor means coupled in parallel therewith, such that the first unilateral conducting means acts in unison with the switching means, both being turned on at about the same time and off at about the same time, the second capacitor means acting in parallel with the first capacitor means during the resonant ring;
• and
• circuit means for pre-regulating voltage presented to the first series circuit.

A resonant forward converter for converting voltage from an input dc voltage source to an output dc voltage for delivery to a load comprising:

• a transformer having a primary and secondary winding wound about a common core element in which the polarities of the windings are matched, said transformer having a magnetizing inductor connected in parallel across one of said windings to provide a resonant ring independent of the load, the magnetizing inductor being naturally supplied by a magnetizing inductance of the transformer;
• switching means connected in series with said primary winding and said input dc voltage source for alternately switching current on and off at a rapid rate through a first series circuit, said switching means causing, when it is turned off, a ring between the magnetizing inductor and a first capacitor means coupled in parallel with the switching means;
• said first series circuit comprising the input dc voltage source, the primary winding of said transformer and the switching means in parallel with said first capacitor means;
• a second series circuit comprising said secondary winding of the transformer in series with a first unilateral conducting means, a parallel output capacitor and said load, said first unilateral conducting means having a second capacitor means coupled in parallel therewith, such that the first unilateral conducting means acts in unison with the switching means, both being turned on at about the same time and off at about the same time, the second capacitor means acting in parallel with the first capacitor means during the resonant ring;
• a leakage inductor connected in a series with one of the windings of the transformer, the leakage inductor being naturally supplied by leakage inductance of the transformer which is negligibly small relative to the magnetizing inductance such the first unilateral conducting means and the switching means both have zero voltage switching transitions;
• and
• circuit means for pre-regulating the voltage presented to the first series circuit.