Full bridge DC-DC converter that applies current doubler

A full bridge DC-DC converter to which a current doubler is applicable is provided and includes a transformer and a switching circuit that converts a high direct current voltage into a high alternating current voltage and then outputs the high alternating current voltage to the primary side of the transformer. In addition, an output circuit receives and processes the output of the secondary side of the transformer and supplies the processed output to an electric load. The output circuit includes a first inductor, a first contact resistor, a second inductor, a second contact resistor, a first diode, a third contact resister, a second diode, and a fourth contact resister.

CROSS-REFERENCE(S) TO RELATED APPLICATIONS

This application claims priority to Korean Patent Application No. 10-2013-0062539, filed on May 31, 2013, which is incorporated herein by reference in its entirety.

BACKGROUND

1. Field of the Invention

The present invention relates to a full bridge DC-DC converter, and particularly, to a full bridge DC-DC converter to which a current doubler is applicable.

2. Description of Related Art

In general, a full bridge direct current-direct current (DC-DC) converter converts a high DC voltage supplied from a high-voltage battery of a vehicle into a low DC voltage and provides an electric load of a vehicle such as an auxiliary battery with the low DC voltage.

In one of the conventional full bridge DC-DC converters, a full bridge DC-DC converter to which a current doubler is applicable is utilized. The full bridge DC-DC converter converts DC input voltage into alternating current (AC) voltage via a primary full bridge circuit (e.g., this full bridge circuit consists of FET (field effect transistor)), converts high AC voltage into low AC voltage via a transformer and outputs low AC voltage to an electric load via a secondary circuit of the transformer, which includes a secondary inductor and a diode. In the full bridge DC-DC converter to which a current doubler is applicable, the transformer is indispensable for reducing high voltage and isolating it from high voltage. When DC current is generated in the transformer, the transformer can be saturated.

In addition, causes exerting an influence on the saturation of the transformer may be mainly divided into causes of the primary side and causes of the secondary side of the transformer. The causes of the primary side may be due to FET Rds-on of the full bridge circuit, and the causes of the secondary side may be due to parasitic resistance of the inductor, a deviation of contact resistance between the inductor and the transformer and a deviation of contact resistance between the output diode and the transformer. A value of FET Rds-on, a value of parasitic resistance of the inductor, and a deviation value of contact resistance between the output diode and the transformer, which influences a saturation of the transformer, can be managed to reduce the effect on a saturation of the transformer.

However, since a coupling area between the inductor and the transformer is substantially small and the inductor is coupled to the transformer by a screw, even when a substantially small torque deviation is generated when the inductor is coupled to the transformer, a deviation of contact resistance between the inductor and the transformer has an effect on a saturation of the transformer.

In the conventional full bridge DC-DC converter as described above, the diode is firstly coupled to the secondary side of the transformer by the screw, thus generating a contact resistance when the inductor is coupled to the transformer by the screw and causing a current unbalance. In addition, DC offset current is generated at the primary side of the transformer due to the current unbalance thus causing a saturation of the transformer to be generated. When the transformer is saturated, current may rapidly increase to generate high current in a switch element. Therefore, a heat and loss of the switch element may increase and noise generation may increase.

SUMMARY

An object of the present is to provide a full bridge DC-DC converter in which the coupling sequence of an output inductor and a diode to be connected to a secondary side of a transformer is changed to minimize the effect of contact resistors, which are formed when the transformer and the inductor are coupled to each other by a screw, on a saturation of the transformer, to thus reduce a heat and a loss of switch elements of the primary side and reduce noise generation.

Other objects and advantages of the present invention may be understood by the following description, and become apparent with reference to the exemplary embodiments of the present invention. In addition, it is obvious to those skilled in the art to which the present invention pertains that the objects and advantages of the present invention can be realized by the means as claimed and combinations thereof.

In order to achieve the above object, a full bridge DC-DC converter to which a current doubler is applicable, according to one aspect of the present invention may include a transformer that reduces a high AC voltage supplied to a primary side thereof and then outputs the AC voltage to a secondary side thereof; a switching circuit that converts a transmitted high DC voltage into a high AC voltage and then outputs the high AC voltage to the primary side of the transformer; and an output circuit that receives and processes the output of the secondary side of the transformer and supplies the processed output to an electric load, the output circuit may include a first inductor having one end connected to one end of the load side, a first contact resistor formed by connecting the other end of the first inductor and one end of the secondary side of the transformer, a second inductor having one end connected to one end of the load side, a second contact resistor formed by connecting the other end of the second inductor and the other end of the secondary side of the transformer, a first diode having an anode connected to a ground line which is the other end of the load side, a third contact resister formed by connecting a cathode of the first diode and electric contacts of the first inductor and the first contact resistor, a second diode having an anode connected to a ground line which is the other end of the load side, and a fourth contact resister formed by connecting a cathode of the second diode and electric contacts of the second inductor and the second contact resistor.

In the output circuit, a first value of the voltage drop caused by a first current flowed through the first contact resister, the first inductor, the load side, the second diode, the fourth contact resistor and the second contact resistor may be the substantially same as a second value of the voltage drop caused by a second current flowed through the second contact resister, the second inductor, the load side, the first diode, the third contact resistor and the first contact resistor, the value of the first current may be the substantially same as that of the second current, and the resistance value of the third contact resistor may be the substantially same as that of the fourth contact resistor.

In addition, the DC of the transformer may be maintained at about zero (0) regardless of a deviation between values of the first contact resistor and the second contact resistor. The first contact resistor may be formed by coupling a wire extended from the first inductor with a wire extended from one end of the secondary side of the transformer by a first screw, the second contact resistor may be formed by coupling a wire extended from the second inductor with a wire extended from the other end of the secondary side of the transformer by a second screw. The third contact resistor may be formed by coupling a portion of the wire extended from one end of the secondary side of the transformer, which is farther away from one end of the secondary side of the transformer than a coupling point obtained by the first screw, with a wire extended from the anode of the first diode by a third screw, and the fourth contact resistor may be formed by coupling a portion of the wire extended from the other end of the secondary side of the transformer, which is farther away from the other end of the secondary side of the transformer than a coupling point obtained by the second screw, with a wire extended from the anode of the second diode by a fourth screw.

In particular, the first screw and the second screw may be the substantially same size and a torque required for coupling the first screw may be the substantially same as that required for coupling the second screw. In addition, the third screw and the fourth screw may be the substantially same size and a torque required for coupling the third screw may be the substantially same as that required for coupling the fourth screw.

The switching circuit may include a first switching element, a second switching element, a third switching element and a fourth switching element, the switching circuit may be driven in a full bridge manner in which the first and third switching elements are simultaneously switched and the second and fourth switching elements are simultaneously switched by a driving clock applied from an exterior, and when a phase and a cycle of the driving clock applied for switching the first and fourth switching elements are fixed, an effective region of the output power transmitted to the primary side of the transformer from the switching circuit may be adjusted by changing a phase of the driving clock applied for switching the second and fourth switching elements.

DETAILED DESCRIPTION

The structure of the present invention is schematically shown in the drawings for illustrating the concept of the present invention, and a description on the known techniques in the structure is omitted. In addition, the exemplary embodiments of the present invention are provided for illustrating more completely to one ordinary skilled in the art. Thus, the shape and size of the elements may be exaggerated in the drawings.

The full bridge DC-DC may convert a high DC voltage transmitted from a power source such as a high voltage battery which is applicable to hybrid vehicles and electric vehicles into a low DC voltage and output the low DC voltage to an electric load such as a low voltage battery and an electric instrument for vehicle.

FIG. 1is an exemplary schematic circuit diagram of a full bridge DC-DC converter in accordance with one exemplary embodiment of the present invention. As shown inFIG. 1, a full bridge DC-DC converter1may be classified into a transformer10, a switching circuit20and an output circuit30. The above classification is provided for the convenience of illustration, a structure of the full bridge DC-DC converter1in accordance with this exemplary embodiment is not limited to this classification.

The transformer10may be configured to transform a substantially high AC voltage transmitted from a primary side into a substantially low AC voltage and may transmit the AC voltage to a secondary side, and an electrical isolation of a vehicle body may be secured from high voltage. [NOTE: Please provide an exemplary or a range of a high AC voltage and a low AC voltage.]

The switching circuit20may be disposed at a primary side of the transformer10and may be configured to convert a substantially high DC voltage transmitted from a power source such as a high voltage battery B into a low AC voltage. The switching circuit20may include a first switching element Q1, a second switching element Q2, a third switching element Q3and a fourth switching element Q4, and the switching circuit may be driven in a full bridge manner in which the first and third switching elements Q1and Q3are simultaneously switched and the second and fourth switching elements Q2and Q4are simultaneously switched by a driving clock applied for driving the switching elements. [NOTE: Please provide an exemplary or a range of a high DC voltage.]

An operation of the full bridge DC-DC converter1in accordance with this exemplary embodiment may be achieved by a driving clock which may be configured to drive the switching circuit20.FIG. 2is an exemplary view of a driving clock that drives the switching circuit for an operation of the full bridge DC-DC converter in accordance with one exemplary embodiment of the present invention. As shown inFIG. 2, by adjusting the driving clock for the third switching element Q3and the second switching element Q2after fixing the driving clock for the first switching element Q1and the fourth switching element Q4, an effective region of the output voltage Vout of the load side may be changed from D1to D1.

FIG. 3is an exemplary view illustrating a structure and an operation of the output circuit inFIG. 1. The output circuit30may be configured to receive an output of a secondary side of the transformer10, process the output through a structure described later and may supply the processed output to the electric load.

As shown inFIG. 3, the output circuit30may include a first inductor Lo1, a first contact resister R1, a second inductor Lo2, a second contact resister R2, a first diode Do1, a third contact resister R3, a second diode Do2and a fourth contact resister R4. A first end of the first inductor Lo1may be connected to a first end of a load side, and the first contact resister R1may be formed by connecting a second end of the first inductor Lo1and a first end of a secondary side of the transformer10. A first end of the second inductor Lo2may be connected to the first end of the load side, and the second contact resister R2may be formed by connecting a second end of the second inductor Lo2and a second end of the secondary side of the transformer10.

An anode of the first diode Do1may be connected to a ground line which is the second end of the load side, and the third contact resister R3may be formed by connecting a cathode of the first diode Do1and electric contacts of the first inductor Lo1and the first contact resistor R1. In addition, an anode of the second diode Do2may be connected to a ground line which is the second end of the load side, and the fourth contact resister R4may be formed by connecting a cathode of the second diode Do2and electric contacts of the second inductor Lo2and the second contact resistor R2.

As shown inFIG. 3, a first branch line P1may be formed by a first current Is1flowed through the first contact resister R1, the first inductor Lo1, the load side Vout, the second diode Do2, the fourth contact resistor R4and the second contact resistor R2. Further, a second branch line P2may be formed by a second current Is2flowed through the second contact resister R2, the second inductor Lo2, the load side Vout, the first diode Do1, the third contact resistor R3and the first contact resistor R1by means of electricity having a polarity opposite to the electricity that forms the first branch line P1. As expressed in equation 1, the value of voltage drop caused by the first branch line P1may be same as the voltage drop caused by the second branch line P2.

In particular, when the resistance value of the third contact resistor R3is almost the same as that of the fourth contact resistor R4and when the value of the first current Is1is almost the same as that of the second current Is2, the Equation 1 may be expressed as the Equation 2.
(Is1×R1)+(Is1×R2)=(Is2×R2)+(Is2×R1)  Equation 2.

In a conventional full bridge DC-DC converter, when a deviation of the value of the contact resistor is generated by a torque adjustment when the transformer and the inductor are coupled with each other, the direct current is generated in the transformer, therefore the transformer may be saturated.

However, in the full bridge DC-DC converter1in accordance with this exemplary embodiment, even when a deviation (R1≠R2) between the values of the first contact resistor R1and the second contact resistor R2is generated by a torque adjustment when the transformer10and the inductors Lo1, Lo2are coupled with each other, the direct current of the transformer10may be maintained at about zero (0) as indicated in the above equations. Therefore, it may be possible to prevent the transformer10from being saturated.

FIG. 4is an exemplary view of a test product for showing mechanical structures of the first to fifth contact resistors shown inFIG. 3. Referring toFIG. 4, the first contact resistor R1may be formed by coupling a wire extended from the first inductor Lo1with a wire extended from a first end of the secondary side of the transformer10by a first screw. The second contact resistor R2may be formed by coupling a wire extended from the second inductor Lo2with a wire extended from a second end of the secondary side of the transformer10by a second screw.

Furthermore, the third contact resistor R3may be formed by coupling a portion of the wire extended from the first end of the secondary side of the transformer10, which is farther away from the first end of the secondary side of the transformer10than a coupling point obtained by the first screw, with a wire extended from the anode of the first diode Do1by a third screw. The fourth contact resistor R4may be formed by coupling a portion of the wire extended from the second end of the secondary side of the transformer10, which is farther away from the second end of the secondary side of the transformer10than a coupling point obtained by the second screw, with a wire extended from the anode of the second diode Do2by a fourth screw.

In particular, the first screw and the second screw may have the substantially same size and a torque required for coupling the first screw may almost be the substantially same as that required for coupling the second screw. Additionally, the third screw and the fourth screw may have the substantially same size and a torque required for coupling the third screw may almost be the substantially same as that required for coupling the fourth screw.

In the full bridge DC-DC converter1in accordance with this exemplary embodiment, the coupling sequence of the output inductor and the diode to be connected to the secondary side of the transformer may be changed to minimize the effect of contact resistors, which are formed when the transformer and the inductor are coupled to each other by the screw, on a saturation of the transformer, thus reducing a heat and a loss of the switch elements of the primary side and reducing a generation of noise. Furthermore, by reducing a drawback of a connection achieved by a screw coupling between the transformer and the inductor, it may be possible to replace a welding process, which is one step of a conventional method of manufacturing a full bridge DC-DC converter and is performed for coupling the secondary side of the transformer and the output inductor, with a screw coupling process.