Patent Publication Number: US-2011069513-A1

Title: Current-Sharing Power Supply Apparatus With Bridge Rectifier Circuit

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a power supply apparatus, and more particularly to a current-sharing power supply apparatus with a bridge rectifier circuit. 
     2. Description of Prior Art 
     In electronic engineering, a DC-to-DC converter is an electronic circuit which converts a source of direct current (DC) from one voltage level to another, and the converted DC voltage is stabilized at the preset voltage value. Generally speaking, the DC-to-DC converter is divided into two categories: one is “step-down” DC-to-DC converter (namely, the output voltage is lower than the input voltage), and the other one is “step-up” DC-to-DC converter (namely, the output voltage is higher than the input voltage). The DC-to-DC converter is mainly applied to a distributed power system. Hence, the DC voltage level of the previous stage is fixed, and the DC voltage level of the next stage can be connected to the corresponding DC-to-DC converter according to the required power. 
     More particularly, the DC-to-DC converter can be separated into two categories: the pulse width modulation (PWM) converter and the resonant converter. The hard-switching operation of the PWM converter introduces the high switching losses and the poor efficiency. Accordingly, the soft-switching technologies have been developed for the resonant converter to reduce the switching losses and increase the efficiency. 
     The DC characteristic of the LLC resonant converter could be divided into ZVS (zero-voltage switching) region and ZCS (zero-current switching) region. A resonant ZCS/ZVS switch (Zero Current/Zero Voltage) where each switch cycle delivers a quantized packet of energy to the converter output, and switch turned-on and turned-off occurs at zero current and voltage, resulting in an essentially lossless switch. Accordingly, the LLC resonant circuit structure is adopted in high-efficiency and high-power power circuits. 
     Reference is made to  FIG. 1  which is a circuit diagram of a prior art LLC resonant circuit. The LLC resonant circuit includes a DC voltage  100 , a square-wave generating circuit  102 , a resonant circuit  104 , a conversion circuit  106 , a rectifier circuit  108 , and a filter circuit  110 . 
     The square-wave generating circuit  102  is composed of two semiconductor components Q T , Q B , and on-state and off-state of the two semiconductor components Q T , Q B  are controlled by a controller  120 . Hence, the square-wave generating circuit  102  can generate two different voltage levels. The resonant circuit  104  is composed of a resonant capacitor Cr and primary windings n 1  of two transformers Ta, Tb. The resonant capacitor Cr is provided to filter a DC component of a pulsating voltage generated by the square-wave generating circuit  102  and an AC component of the pulsating voltage is resonated. Also, each of the primary windings n 1  of the transformers Ta, Tb is provided to transform electrical energy into magnetic energy, and the transformed magnetic energy is delivered to corresponding secondary windings of the transformers Ta, Tb. 
     The rectifier circuit  108  is composed of four rectifier diodes D1, D2, D3, D4. The function of rectifying and filtering is implemented based on the single-directional turned-on property of the diodes D1, D2, D3, D4 and the charging and discharging property of the filter capacitor Co. The description of operating the LLC resonant converter is as follows. The filter circuit  110  includes a filter capacitor Cout to reduce a voltage ripple of the DC output voltage to smooth the variation of the DC output voltage based on the charging and discharging property of the filter capacitor Cout. 
     The detailed operation is explained as follows. First, a pulsating voltage is generated at a node A when the DC voltage  100  is provided to the square-wave generating circuit  102 . Afterward, the resonant capacitor Cr filters the DC component of the pulsating voltage and the AC component of the pulsating voltage is resonated when the pulsating voltage passes through the resonant circuit  104 . Afterward, the resonated AC voltage and resonated AC current are outputted at the conversion circuit  106 , namely the secondary windings n 2  of the transformers Ta, Tb. Finally, the AC voltage is rectified by the rectifier circuit  108  and is filtered a filter circuit  110  to generate a DC voltage which is outputted to a voltage output terminal Vout. 
     The self inductance (including the leakage inductance and the magnetizing inductance) of the transformer is the main energy-storage component of the resonant circuit. Hence, it is careful to handle the winding connection for multiple transformers are used when the high-power circuit in-series or in-parallel resonant circuits are used when the high-power circuit is applied. In addition, the amount of the rectifier diodes and the turns of the secondary windings are large, thus increasing the losses and reduce the efficiency. 
     SUMMARY OF THE INVENTION 
     The purpose of the present invention is to provide a current-sharing power supply apparatus with a bridge rectifier circuit to reduce the amount of the secondary windings of the transformers to minimize size of the power supply apparatus. 
     In order to achieve the object mentioned above, the current-sharing power supply apparatus with the bridge rectifier circuit includes a square-wave generating circuit, a resonant circuit, a conversion circuit, a rectifier circuit, and a filter circuit. 
     The conversion circuit has two transformers, and each of the transformers has a primary winding and at least one secondary winding. More particularly, the secondary windings of the two transformers are electrically connected in series. 
     The square-wave generating circuit is electrically connected to a DC voltage to switch the DC voltage into a pulsating voltage. The resonant circuit is electrically connected to the square-wave generating circuit, and the resonant circuit has a first capacitor and the primary windings of the transformers. More particularly, the first capacitor is a resonant capacitor. 
     The rectifier circuit has at least four switch components. Also, the rectifier circuit is electrically connected to the secondary windings of the transformers to rectify an AC voltage outputted from the secondary windings into a rectified voltage, and the rectified voltage is outputted to at least one voltage output terminal. More particularly, the switch components are rectifier diodes. 
     In addition, the rectifier diodes can be replaced by the MOSFETs to compose a synchronous rectify circuit. More particularly, the synchronous rectify circuit further has one diode electrically connected between a drain and a source of each MOSFET. 
     The current-sharing power supply apparatus further includes a filter circuit, which is electrically connected to the rectifier circuit. The filter circuit has at least one second capacitor, which is a filter capacitor. The filter circuit is provided to reduce a voltage ripple of the DC output voltage to smooth the variation of the DC output voltage based on the charging and discharging property of the second capacitor. 
     Accordingly, the secondary windings of two transformers are electrically connected in series to balance the magnetic flux of the two transformers to provide a current-sharing function. In addition, the amount of the diodes and the turns of the secondary windings is less to reduce the losses and increase the efficiency. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. Other advantages and features of the invention will be apparent from the following description, drawings and claims. 
    
    
     
       BRIEF DESCRIPTION OF DRAWING 
       The features of the invention believed to be novel are set forth with particularity in the appended claims. The invention itself, however, may be best understood by reference to the following detailed description of the invention, which describes an exemplary embodiment of the invention, taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a circuit diagram of a prior art LLC resonant circuit; 
         FIG. 2  is a circuit diagram of a first embodiment of a current-sharing power supply apparatus according to the present invention; 
         FIG. 3  is a circuit diagram of a second embodiment of the current-sharing power supply apparatus; 
         FIG. 4  is a circuit diagram of a third embodiment of the current-sharing power supply apparatus; 
         FIG. 5  is a circuit diagram of a fourth embodiment of the current-sharing power supply apparatus; 
         FIG. 6  is a circuit diagram of a fifth embodiment of the current-sharing power supply apparatus; 
         FIG. 7  is a circuit diagram of a sixth embodiment of the current-sharing power supply apparatus; and 
         FIG. 8(   a ) to  FIG. 8(   h ) are voltage waveforms of the main nodes of the current-sharing power supply apparatus. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In cooperation with attached drawings, the technical contents and detailed description of the present invention are described thereinafter according to a preferable embodiment, being not used to limit its executing scope. Any equivalent variation and modification made according to appended claims is all covered by the claims claimed by the present invention. 
     Reference will now be made to the drawing figures to describe the present invention in detail.  FIG. 2  is a circuit diagram of a first embodiment of a current-sharing power supply apparatus according to the present invention; and  FIG. 8(   a ) to  FIG. 8(   g ) are voltage waveforms of the main nodes of the current-sharing power supply apparatus. The current-sharing power supply apparatus with a bridge rectifier circuit is a DC-to-DC converter to convert a DC voltage  200  at a voltage input terminal Vin, as shown in  FIG. 8(   b ), from one voltage level to another voltage level required for a back-end circuit. The current-sharing power supply apparatus includes a square-wave generating circuit  202 , a resonant circuit  204 , a conversion circuit  206 , and a rectifier circuit  208 . 
     The conversion circuit  206  is electrically connected to the resonant circuit  204 . Also, the conversion circuit  206  has two transformers T1, T2, and each of the transformers Ta1, T2 has a primary winding n 1  and a secondary winding n 2 . More particularly, the left-side winding of the conversion circuit  206  is the primary winding n 1 , and the right-side winding of the conversion circuit  206  is the secondary winding n 2 . The first transformer T1 has a first primary winding n 11  and a corresponding first secondary winding n 21 . Also, the second transformer T2 has a second primary winding n 12  and a corresponding second secondary winding n 22 . More particularly, the first secondary winding n 21  is connected in series to the second secondary winding n 22 , and the first primary winding n 11  is connected in parallel to the second primary winding n 12 . 
     The square-wave generating circuit  202  is a half-bridge circuit which is composed of two semiconductor components, namely, a first semiconductor component Q1, a second semiconductor component Q2. Also, the square-wave generating circuit  202  is electrically connected to the voltage input terminal Vin. The first semiconductor component Q1 and the second semiconductor component Q2 are controlled by a controller  800  to be alternately in a turned-on state and a turned-off state to generate a pulsating voltage Vp at a node p, as shown in  FIG. 8(   b ). 
     The resonant circuit  204  is electrically connected to the square-wave generating  202 . Also the resonant circuit  204  is composed of a first capacitor C1 and the primary windings n 1  of the transformers T1, T2. More particularly, the first capacitor C1 is a resonant capacitor, which is provided to filter a DC component of the pulsating voltage Vp. Besides, an AC component of the pulsating voltage Vp is resonated with the primary windings n 1  of the transformers T1, T2 to generate a resonated voltage Vr at a node r, as shown in  FIG. 8(   c ). The resonated voltage Vr is coupled from the primary windings n 1  of the transformers T1, T2 to the secondary windings n 2  of the transformers T1, T2. 
     The rectifier circuit  208  includes four switch components, namely, a first switch component S1, a second switch component S2, a third switch component S3, and a fourth switch component S4 to form a full-bridge rectifier circuit. The rectifier circuit  208  is electrically connected to the secondary windings n 2  of the transformers T1, T2 to rectify the coupled resonated voltage Vr to generate a rectified voltage Vx at a node x. In this embodiment, the first switch component S1, the second switch component S2, the third switch component S3, and the fourth switch component S4 are all rectifier diodes. 
     The current-sharing power supply apparatus further includes a filter circuit  210 . The filter circuit  210  has a second capacitor C2, and the filter circuit  210  is electrically connected between the rectifier circuit  208  and the voltage output terminal Vout. More particularly, the second capacitor C2 is a filter capacitor to reduce a voltage ripple of the DC output voltage, as shown in  FIG. 8(   e ), to smooth the variation of the DC output voltage based on the charging and discharging property of the second capacitor C2. 
     In this embodiment, the description of operating the power supply apparatus is as follows. The voltage at the node p is a positive voltage referenced to a ground when the first semiconductor component Q1 of the square-wave generating circuit  202  is turned-on and the second semiconductor component Q2 of the square-wave generating circuit  202  is turned-off. Hence, the voltages at dot ends of the primary windings n 1  and the secondary windings n 2  of the transformers T1, T2 of the conversion circuit  206  are positive. The first switch component S1 and the fourth switch component S4 of the rectifier circuit  208  are turned-on to form a current loop. 
     The voltage at the node p is a negative voltage referenced to a ground when the first semiconductor component Q1 of the square-wave generating circuit  202  is turned-off and the second semiconductor component Q2 of the square-wave generating circuit  202  is turned-on. Hence, the voltages at dot ends of the primary windings n 1  and the secondary windings n 2  of the transformers T1, T2 of the conversion circuit  206  are negative. The second switch component S2 and the third switch component S3 of the rectifier circuit  208  are turned-on to form a current loop. 
     Reference is made to  FIG. 3  which is a circuit diagram of a second embodiment of the current-sharing power supply apparatus. The current-sharing power supply apparatus includes a square-wave generating circuit  302 , a resonant circuit  304 , a conversion circuit  306 , a rectifier circuit  208 , and a filter circuit  310 . More particularly, the connection relationship among the square-wave generating circuit  302 , the resonant circuit  304 , the conversion circuit  306 , and the filter circuit  410  is the same as that shown in  FIG. 2 . However, the components of the rectifier-filter circuit  308  are only different. In this embodiment, a first switch component S1′, a second switch component S2′, a third switch component S3′, and a fourth switch component S4 can be MOSFETs to replace the rectifier diodes to compose a synchronous rectifier. 
     The filter circuit  308  further has one diode electrically connected between a drain and a source of each MOSFET. The four diodes are used to avoid generating a high breakdown voltage, which tends to damage the four MOSFETs S1′˜S4′, and further to increase switching speed of the four MOSFETs S1′˜S4′. In addition, a switch driving circuit (not shown) is electrically connected to a gate of each MOSFET to drive and control the MOSFETs S1˜S4′. 
     Reference is made to  FIG. 4  which is a circuit diagram of a third embodiment of the current-sharing power supply apparatus with multiple voltage output terminals. The current-sharing power supply apparatus includes a square-wave generating circuit  402 , a resonant circuit  404 , a conversion circuit  406 , a rectifier circuit  408 , and a filter circuit  410 . More particularly, the connection relationship among the square-wave generating circuit  402  and the resonant circuit  404  is the same as that shown in  FIG. 2 . However, the amount of the switch components of the rectifier circuit  408  and the amount of the capacitors of the filter circuit  410  are different from that shown in  FIG. 2 . 
     The conversion circuit  406  has two first windings n 1 , namely, a first primary winding n 11  and a second primary winding n 12 ; and four secondary windings n 2 , namely, a first secondary winding n 21 , a second secondary winding n 22 , a third secondary winding n 23 , and a fourth secondary winding n 24 . Also, the first primary winding n 11  is corresponding to the first secondary winding n 21  and the third secondary winding n 23 ; and the second primary winding n 12  is corresponding to the second secondary winding n 22  and fourth secondary winding n 24 . More particularly, the first secondary winding n 21  is electrically connected to the second secondary winding n 22  in series; and the third secondary winding n 23  is electrically connected to the fourth secondary winding n 24  in series. 
     The rectifier circuit  408  includes six switch components, namely, a first switch component S1, a second switch component S2, a third switch component S3, a fourth switch component S4, a fifth switch component S5, and a sixth switch component S6. The rectifier circuit  408  is a bridge rectifier circuit which is composed of the first switch component S1, the second switch component S2, the third switch component S3, and the fourth switch component S4. Also, the full-bridge rectifier circuit  408  is electrically connected to the first secondary winding n 21  and the second secondary winding n 22 . The fifth switch component S5 and the sixth switch component S6 are electrically connected to the third secondary winding n 23  and the fourth secondary winding n 24 , respectively, to form a full-wave rectifier circuit. The rectifier circuit  408  is provided to rectify the coupled resonated voltage Vr outputted from the secondary windings n 2  of the transformers T1, T2 to generate a rectified voltage Vx1 and a rectified voltage Vx2 at a node x1 and a node x2, respectively, as shown in  FIG. 8(   f ). 
     The filter circuit  410  has a third capacitor C3 and a fourth capacitor C4. More particularly, the third capacitor C3 is electrically connected to the bridge rectifier circuit, and the fourth capacitor C4 is electrically connected to the full-wave rectifier circuit. Also, the third capacitor C3 and the fourth capacitor C4 are filter capacitors to reduce a voltage ripple of the DC output voltage to smooth the variation of the DC output voltage based on the charging and discharging property of the third capacitor C3 and the fourth capacitor C4. The filtered voltage is outputted to back-end circuits via a first voltage output terminal Vout1 and a second voltage output Vout2, as shown in  FIG. 8(   g ). 
     Reference is made to  FIG. 5  which is a circuit diagram of a fourth embodiment of the current-sharing power supply apparatus. In this embodiment, each of the above-mentioned half-bridge square-wave generating circuits can be replaced by a full-bridge square-wave generating circuit  502 . The full-bridge square-wave generating circuit  502  is composed of four semiconductor components, namely, a first semiconductor component Q1, a second semiconductor component Q2, a third semiconductor component Q3, and a fourth semiconductor component Q4, respectively. More particularly, the first semiconductor component Q1 and the second semiconductor component Q2 are electrically connected together and further electrically connected to a controller  800 . Also, the third semiconductor component Q3 and the fourth semiconductor component Q4 are electrically connected together and further electrically connected to the controller  800 . A first primary winding n 11  and a second primary winding n 12  of a resonant circuit  504  are electrically connected in series, and then are electrically connected to the full-bridge square-wave generating circuit  502 . 
     In this embodiment, the description of operating the power supply apparatus is as follows. First, The first and second semiconductor components Q1, Q2 and the third and fourth semiconductor component Q3, Q4 are controlled by the controller  800  to be alternately in a turned-on state and a turned-off state to generate a pulsating voltage Vp at a node p and a pulsating voltage Vq at a node q, respectively, as shown in  FIG. 8(   h ). Afterward, a first capacitor C1 of the resonant circuit  504  is resonated with the primary winding n 1  of the conversion circuit  506  to produce a resonated voltage Vr. The resonated voltage Vr is coupled from the primary winding n 1  to the secondary winding n 2 . The resonated voltage Vr is rectified by a filter circuit  508 , and is filtered by a filter circuit  510  to reduce a voltage ripple of the DC output voltage to smooth the variation of the DC output voltage based on the charging and discharging property of the second capacitor C2. 
     The main feature of the power supply apparatus is variation of connecting manner for the secondary windings, so the primary windings of the transformers can be electrically connected to varied resonant circuits, such as shown in  FIG. 6  and  FIG. 7 . Reference is made to  FIG. 6  which is a circuit diagram of a fifth embodiment of the power supply apparatus. The primary windings n 1  of the transformers T1, T2 of the resonant circuit  604  are electrically connected in series. The operation voltages of the primary windings n 1  are generated by dividing the voltage outputted from the square-wave generating circuit  602 . Reference is made to  FIG. 7  which is a circuit diagram of a sixth embodiment of the power supply apparatus. Two resonant capacitors C11, C12 of the resonant circuit  704  are electrically connected in series to the first primary winding n 11  and the secondary primary winding n 12 , respectively, to filter the DC component and pass the AC component. 
     Accordingly, the secondary windings of two transformers are electrically connected in series to balance the magnetic flux of the two transformers to provide a current-sharing function. In addition, the amount of the diodes and the turns of the secondary windings is less to reduce the losses and increase the efficiency. 
     Although the present invention has been described with reference to the preferred embodiment thereof, it will be understood that the invention is not limited to the details thereof Various substitutions and modifications have been suggested in the foregoing description, and others will occur to those of ordinary skill in the art. Therefore, all such substitutions and modifications are intended to be embraced within the scope of the invention as defined in the appended claims.