Enhanced flyback converter

Abstract

A DC/DC flyback converter that exhibits reduced switch and transformer voltage stresses in comparison to known flyback converters. The flyback converter also employs soft switching. Embodiments of such flyback converters may be used, without limitation, in electric vehicles and hybrid electric vehicles. A front-stage of the flyback converter comprises a DC/AC step-down circuit that may be separately used for various purposes.

What is claimed is: 
     
         1 . A flyback DC/DC converter, comprising:
 a circuit having a high-voltage side and a low-voltage side separated by a transformer;   a plurality of switches on the high-voltage side and a plurality of switches on the low-voltage side;   a plurality of components that are adapted to store energy in an electric field on the high-voltage side, and at least one such component on the low-voltage side;   at least one component that is adapted to store energy in a magnetic field on the low-voltage side;   wherein, the switches are actuatable in various combinations at a selected switching frequency to produce both active modes and deadband modes of operation within a given switching period; and   wherein the at least one component that stores energy in a magnetic field is adapted to store energy only in active modes when an associated high-voltage side switch is turned on, and to release energy to a load only in deadband modes when the associated high-voltage side switch is turned off.   
     
     
         2 . The flyback converter of  claim 1 , wherein the switches are passive and active power devices. 
     
     
         3 . The flyback converter of  claim 1 , wherein:
 a pair of components adapted to store energy in a magnetic field are present on the low-voltage side;   a pair of switches are located on the high-voltage side, each of the switches corresponding to a given one of the components adapted to store energy in a magnetic field;   wherein, when one of the switches is on, a corresponding one of the magnetic field energy storing components is adapted to store energy, and when the same switch is off, the same magnetic field energy storing component is adapted to release energy to a load; and   wherein, when the other of the switches is on, the other of the magnetic field energy storing components is adapted to store energy, and when the same switch is off, the same magnetic field energy storing component is adapted to release energy to the load.   
     
     
         4 . The flyback converter of  claim 1 , wherein:
 a component adapted to store energy in a magnetic field is present on the low-voltage side, the component having two coupled windings;   a pair of switches are located on the high-voltage side, each of the switches corresponding to a given one of the components adapted to store energy in a magnetic field;   wherein, when one of the switches is on, a corresponding one of the windings of the magnetic field energy storing component is adapted to store energy, and when the same switch is off, the same winding of the magnetic field energy storing component is adapted to release energy to a load; and   wherein, when the other of the switches is on, the other of the windings of the magnetic field energy storing component is adapted to store energy, and when the same switch is off, the same winding of the magnetic field energy storing component is adapted to release energy to the load.   
     
     
         5 . The flyback converter of  claim 1 , wherein the converter is adapted to operate with a symmetrical duty ratio and a variable deadband ratio. 
     
     
         6 . The flyback converter of  claim 1 , wherein the high-voltage side is a step-down DC/AC circuit having a step-down ratio of approximately 3:1, and an AC output voltage having a peak value that is approximately ⅓ of the input voltage supplied to the converter. 
     
     
         7 . The flyback converter of  claim 1 , wherein an output voltage of the converter is regulatable by changing the switch duty ratio and deadband of the high-voltage side switches. 
     
     
         8 . The flyback converter of  claim 1 , wherein the high-voltage side switches are adapted to be driven with a symmetrical duty ratio and the low-voltage side switches are adapted to operate in synchronous rectification. 
     
     
         9 . The flyback converter of  claim 1 , wherein the low-voltage side circuit is selected from the group consisting of a traditional rectifying circuit and a ripple cancelling circuit. 
     
     
         10 . The flyback converter of  claim 1 , wherein the circuit is adapted such that the voltage stress on the switches is approximately ⅔ of the input voltage supplied to the converter and the voltage stress on the transformer is approximately ⅓ of the input voltage supplied to the converter when the converter is in operation. 
     
     
         11 . The flyback converter of  claim 1 , wherein the low-voltage side switches exhibit zero current switching during both turn-on and turn-off thereof, and the high-voltage side switches exhibit zero current switching during turn-on thereof. 
     
     
         12 . The flyback converter of  claim 1 , wherein the circuit is adapted such that there will be four active modes and four deadband modes within a given switching period when the converter is operated in steady state. 
     
     
         13 . A flyback DC/DC converter, comprising:
 a circuit having a front-stage side and a post-stage side separated by a transformer, the front-stage side adapted for connection to an input voltage source;   a plurality of components that store energy in an electric field on the front-stage side, and at least one such component on the post-stage side;   at least one component that stores energy in a magnetic field on the post-stage side; and   a plurality of switches located on both the front-stage side and the post-stage side, the switches being actuatable in various combinations and at a selected switching frequency within a given switching period;   wherein, in steady-state operation, the voltage stress on the switches is about ⅔ of the input voltage and the voltage stress on the transformer is about ⅓ of the input voltage; and   wherein the post-stage side switches exhibit zero current switching during both turn-on and turn-off thereof, and the front-stage side switches exhibit zero current switching during turn-on thereof.   
     
     
         14 . The flyback converter of  claim 13 , wherein the converter is adapted to operate with a symmetrical duty ratio and a variable deadband ratio. 
     
     
         15 . The flyback converter of  claim 13 , wherein the front-stage side is a step-down DC/AC circuit having a step-down ratio of approximately 3:1 and an AC output voltage having a peak value that is approximately ⅓ of the input voltage. 
     
     
         16 . The flyback converter of  claim 13 , wherein an output voltage of the converter is regulatable by changing the switch duty ratio and deadband of the high-voltage side switches. 
     
     
         17 . The flyback converter of  claim 13 , wherein the front-stage side switches are adapted to be driven with a symmetrical duty ratio and the post-stage side switches are adapted to operate in synchronous rectification. 
     
     
         18 . The flyback converter of  claim 13 , wherein the post-stage side circuit is selected from the group consisting of a traditional rectifying circuit and a ripple cancelling circuit. 
     
     
         19 . A method of performing DC/DC power conversion, comprising:
 (a) providing a flyback DC/DC converter circuit, comprising:
 a high-voltage side in the form of a step-down DC/AC circuit that is adapted for connection to an input voltage source and has a step-down ratio of approximately 3:1, and a low-voltage side selected from the group consisting of a traditional rectifying circuit and a ripple cancelling circuit, the high-voltage side and the low-voltage side separated by a transformer, 
 a plurality of switches on the high-voltage side and a plurality of switches on the low-voltage side, 
 a plurality of components that are adapted to store energy in an electric field on the high-voltage side, and at least one such component on the low-voltage side, and 
 at least one component that is adapted to store energy in a magnetic field on the low-voltage side; 
   (b) actuating the switches in various combinations at a selected switching frequency to produce both active modes and deadband modes of operation within a given switching period; and   (c) causing the at least one component that stores energy in a magnetic field to store energy only in active modes when an associated high-voltage side switch is turned on, and to release energy to a load only in deadband modes when the associated high-voltage side switch is turned off;   such that, in steady-state operation, the voltage stress on the switches is about ⅔ of the input voltage and the voltage stress on the transformer is about ⅓ of the input voltage.   
     
     
         20 . The method of  claim 19 , wherein the converter is operated with a symmetrical duty ratio and a variable deadband ratio. 
     
     
         21 . The method of  claim 19 , wherein an output voltage of the converter is regulated by changing the switch duty ratio and deadband of the high-voltage side switches. 
     
     
         22 . The method of  claim 19 , wherein the high-voltage side switches are driven with a symmetrical duty ratio and the low-voltage side switches are operated in synchronous rectification. 
     
     
         23 . The method of  claim 19 , wherein:
 a pair of components adapted to store energy in a magnetic field are provided on the low-voltage side;   a pair of switches are provided on the high-voltage side, with each of the switches corresponding to a given one of the components adapted to store energy in a magnetic field;   wherein, when one of the switches is turned on, a corresponding one of the magnetic field energy storing components stores energy, and when the same switch is turned off, the same magnetic field energy storing component releases energy to a load; and   wherein, when the other of the switches is turned on, the other of the magnetic field energy storing components stores energy, and when the same switch is turned off, the same magnetic field energy storing component releases energy to the load.   
     
     
         24 . The method of  claim 19 , wherein:
 a component adapted to store energy in a magnetic field is provided on the low-voltage side, the component having two coupled windings;   a pair of switches are provided on the high-voltage side, each of the switches corresponding to a given one of the components adapted to store energy in a magnetic field;   wherein, when one of the switches is turned on, a corresponding one of the windings of the magnetic field energy storing component stores energy, and when the same switch is turned off, the same winding of the magnetic field energy storing component releases energy to a load; and   wherein, when the other of the switches is turned on, the other of the windings of the magnetic field energy storing component stores energy, and when the same switch is turned off, the same winding of the magnetic field energy storing component releases energy to the load.