Patent Publication Number: US-7709974-B2

Title: Power supply device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of Korean Patent Application No. 10-2007-0133404 filed with the Korea Intellectual Property Office on Dec. 18, 2007, the disclosure of which is incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a power supply device which can detect an open load through electromagnetic induction. 
   2. Description of the Related Art 
   In general, since LCD products such as LCD TVs or LCD monitors cannot emit light by themselves, a backlight device for providing light to an LCD panel is used therein. Such a backlight device provides light by using a plurality of discharge lamps. The resistance value of the respective lamps when the backlight device is initially driven is different from that of the lamps when the backlight device is normally driven. Therefore, when the lamps are driven in parallel, a current balance should be maintained using a current balancing transformer. 
   Further, when the lamps adopted in the backlight device are driven in parallel, the brightness of the lamps should be constantly maintained and adjusted. For this, a power supply unit of the backlight device is provided with a feedback circuit and a protection circuit. The feedback circuit receives the currents of the lamps to constantly maintain the lamp currents, and the protection circuit protects the lamps and the power supply unit when an excessive voltage is applied to the lamps. 
   Hereinafter, a conventional power supply device will be described with reference to  FIG. 1 . 
     FIG. 1  is a circuit diagram of a conventional power supply device. 
   As shown in  FIG. 1 , the conventional power supply device includes a power supply unit  110 , a current balancing unit  120 , a detection unit  130 , and a control unit  140  and drives a plurality of loads L 1  to L 6  with constant brightness. 
   The power supply unit  110  is connected to the plurality of loads L 1  to L 6 , the current balancing unit  120 , and the control unit  140  and is controlled by the control unit  140  so as to output a driving voltage Vin for driving the plurality of loads L 1  to L 6 . 
   The current balancing unit  120  is composed of a plurality of transformers T 1  to T 6  having primary and secondary sides. The current balancing unit  120  receives the driving voltage Vin output from the power supply unit  110  so as to balance currents of the driving voltage Vin. Then, the current balancing unit  120  supplies the driving voltage with a constant magnitude to the respective loads L 1  to L 6 . 
   The number of the transformers T 1  to T 6  is equal to the number of the loads L 1  to L 6  such that the transformers T 1  to T 6  are connected to the respective loads L 1  to L 6  one by one. The primary sides of the transformers T 1  to T 6  receive the driving voltage Vin to supply to the respective loads L 1  to L 6 . Further, the secondary sides thereof are connected in series to each other so as to maintain a current balance of the driving voltage Vin applied from the primary sides. 
   The detection unit  130  is connected to the current balancing unit  120  and the control unit  140  and includes a plurality of voltage dividing sections  131  to  136 , first to sixth diodes D 1  to D 6 , and a capacitor C 0 . The detection unit  130  detects a current flowing in the current balancing unit  120  so as to output a detection signal P corresponding to the detected current. 
   At this time, the plurality of voltage dividing sections  131  to  136  are connected to the secondary sides of the respective transformers T 1  to T 6  and respectively have two resistors. The voltage dividing sections  131  to  136  receive and divide a voltage corresponding to the current flowing in the connected transformers. 
   The first to sixth diodes D 1  to D 6  receive and output the voltages divided by the plurality of voltage dividing sections  131  and  136 , and the capacitor C 0  smoothes the divided voltages applied through the first to sixth diodes D 1  to D 6  to output as a detection signal P. 
   The control unit  140  is connected to the detection unit  130  and the power supply unit  110 . When the detection signal P delivered through the detection unit  130  is larger or smaller than a preset reference voltage, the control unit  140  judges that one or more of the loads L 1  to L 6  are opened or short-circuited. Then, the control unit  140  outputs a control signal S for controlling the power supply unit  110 . 
   Accordingly, when the loads are opened or short-circuited, the control unit  140  controls the power supply unit  110  so as to control the output of the driving voltages Vin is controlled. Then, it is possible to protect the plurality of loads L 1  to L 6  and the power supply device. 
   However, the conventional power supply device has the following problems. 
   In the conventional power supply device, one transformer should be provided to drive one load. In  FIG. 1 , six of the transformers T 1  to T 6  should be provided in the current balancing unit  120  to drive six of the loads L 1  to L 6 . Therefore, as the number of loads increases, the volume of the power supply device increases, and the circuit becomes complex. 
   Further, the detection unit  130  of the conventional power supply device is directly connected to the plurality of transformers T 1  to T 6  required for insulation design. Therefore, there are difficulties in applying the detection unit  130  to a load requiring a high voltage. 
   SUMMARY OF THE INVENTION 
   An advantage of the present invention is that it provides a power supply device in which a current balancing unit is composed of a plurality of transformers having primary, secondary, tertiary sides such that the volume thereof can be reduced, and a detection unit detects currents flowing the current balancing unit through electromagnetic induction. Therefore, it is easily to achieve insulation design. 
   Additional aspects and advantages of the present general inventive concept will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the general inventive concept. 
   According to an aspect of the invention, a power supply device comprises a power supply unit that supplies a driving voltage for driving at least one or more loads; a current balancing unit that maintains a current balance of the driving voltage supplied to the respective loads; a detection unit that detects currents flowing in the current balancing unit through electromagnetic induction so as to output a detection signal; and a control unit that receives the detection signal to judge whether the loads are opened or not and outputs a control signal for controlling the magnitude of the driving voltage. 
   Preferably, the current balancing unit is composed of a plurality of transformers which respectively have primary, secondary, and tertiary sides and are respectively connected to two loads so as to supply the driving voltage to the loads. In each of the transformers, the primary and secondary sides thereof are connected to different loads from each other, and the tertiary side thereof is connected to the primary and secondary sides of a neighboring transformer. 
   Preferably, the detection unit includes a plurality of antenna sections that detect the currents flowing in the current balancing unit through electromagnetic induction; a plurality of voltage dividing sections that receive and divide a voltage corresponding to the currents detected by the respective antenna sections; a plurality of diodes of which the anodes are connected to the respective voltage dividing sections and the cathodes are connected to each other so as to output the divided voltages; and a capacitor that smoothes the voltages output through the plurality of diodes to output as a detection signal. 
   Preferably, the plurality of antenna sections detect the driving voltage output from the power supply unit or the currents flowing in the current balancing unit through electromagnetic induction, and the plurality of voltage dividing sections respectively have two division resistors connected in series to each other. 
   Preferably, the current balancing unit is composed of a plurality of transformers which respectively have primary and secondary sides and are respectively connected to one load so as to supply the driving voltage to the load. In each of the transformers, the primary side thereof is connected to the load, and the secondary side thereof is connected to the secondary side of a neighboring transformer. 
   According to another aspect of the invention, a power supply device comprises a power supply unit that supplies a driving voltage for driving at least one or more loads; a current balancing unit that maintains a balance of currents flowing in the respective loads; a detection unit that detects the currents flowing in the current balancing unit through electromagnetic induction so as to output a detection signal; and a control unit that receives the detection signal to judge whether the loads are opened or not, and outputs a control signal for controlling the magnitude of the driving voltages. 
   Preferably, the current balancing unit is composed of a plurality of transformers which respectively have primary, secondary, and tertiary sides and are respectively connected to two loads so as to balance the currents flowing in the respective loads. In each of transformers, the primary and secondary sides thereof are connected to different loads from each other, and the tertiary side thereof is connected to the primary and secondary sides of a neighboring transformer. 
   Preferably, the detection unit includes a plurality of antenna sections that detect the currents flowing in the current balancing unit through electromagnetic induction; a plurality of voltage dividing sections that receive and divide a voltage corresponding to the currents detected by the respective antenna sections; a plurality of diodes of which the anodes are connected to the respective voltage dividing sections and the cathodes are connected to each other so as to output the divided voltages; and a capacitor that smoothes the voltages output through the plurality of diodes to output as a detection signal. 
   Preferably, the plurality of antenna sections detect the driving voltage output from the power supply unit or the currents flowing in the current balancing unit through electromagnetic induction, and the plurality of voltage dividing sections respectively have two division resistors connected in series to each other. 
   Preferably, the current balancing unit is composed of a plurality of transformers which respectively have primary and secondary sides and are respectively connected to one load so as to balance the current flowing through the load. In each of the transformers, the primary side thereof is connected to the load, and the secondary side thereof is connected to the secondary side of a neighboring transformer. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and/or other aspects and advantages of the present general inventive concept will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
       FIG. 1  is a circuit diagram of a conventional power supply device; 
       FIG. 2  is a circuit diagram of a power supply device according to a first embodiment of the invention; 
       FIG. 3  is a circuit diagram of a power supply device according to a modification of the first embodiment of the invention; 
       FIG. 4  is a circuit diagram of a power supply device according to the second embodiment of the invention; and 
       FIG. 5  is a circuit diagram of a power supply device according to a modification of the second embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Reference will now be made in detail to the embodiments of the present general inventive concept, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. The embodiments are described below in order to explain the present general inventive concept by referring to the figures. 
   Hereinafter, a power supply device for detecting an open load using electromagnetic induction according to the present invention will be described in detail with reference to the accompanying drawings. 
   First Embodiment 
     FIG. 2  is a circuit diagram of a power supply device according to a first embodiment of the invention. 
   As shown in  FIG. 2 , the power supply device according to the first embodiment of the invention includes a power supply unit  210  which outputs a driving voltage Vin for driving a plurality of loads L 1  to L 6 , a current balancing unit  220  for balancing currents of the driving voltage Vin, a detection unit  230  for detecting currents flowing in the current balancing unit  220 , and a control unit  240  for controlling the power supply unit  210 . 
   The power supply unit  210  is connected to the plurality of loads L 1  to L 6 , the current balancing unit  220 , and the control unit  240  and is controlled by the control unit  240  so as to output a driving voltage Vin for driving the plurality of loads L 1  to L 6 . 
   The current balancing unit  220 , which is composed of first to third transformers T 1  to T 3 , is connected to the power supply unit  210 , the plurality of loads L 1  to L 6 , and the detection unit  230  and serves to balance currents of the driving voltage Vin output from the power supply unit  210  so as to supply first to sixth currents i 1  to i 6  to the respective loads L 1  to L 6 , the first to sixth currents i 1  to i 6  having the same magnitude. 
   Each of the first to third transformers T 1  to T 3  has an El-core structure that has primary, secondary, and tertiary sides. The primary and secondary sides are commonly connected to each other so as to be connected to the tertiary side of a neighboring transformer. In particular, the respective tertiary sides of the first to third transformers T 1  to T 3 , which are connected to the power supply unit  210 , receive the driving voltage Vin supplied from the power supply unit  210  and then induce the driving voltage Vin to the primary and secondary sides. 
   Accordingly, the current balancing unit  220  can balance currents i 1  to i 6  flowing in the first to third transformers T 1  to T 3 , and then supplies the balanced currents i 1  to i 6  to the plurality of loads L 1  to L 6 , thereby uniformly maintaining the brightness of the loads L 1  to L 6 . 
   The current balancing unit  220  configured in such a manner requires only three of the first to third transformers T 1  to T 3  to drive six of the loads L 1  to L 6 , while the conventional power supply device requires six transformers to drive six loads. Therefore, it is possible to reduce the size of the current balancing unit  220 , which makes it possible to reduce the entire size of the power supply device. 
   As the number of transformers provided in the current balancing unit  220  decreases from six to three, the complexness of the circuit becomes so low that the circuit can be simplified. 
   In the invention, the power supply device for driving six loads L 1  to L 6  has been described. Therefore, in a power supply device for driving 12 loads, the number of transformers decreases from 12 to 6. Accordingly, as the number of loads increase, a circuit can be further simplified, and the volume of the circuit can be reduced. 
   The detection unit  230  includes first to third antenna sections S 1  to S 3 , first to third voltage dividing sections  231  to  233 , first to third diodes D 1  to D 3 , and a capacitor C 0 . The detection unit  230 , which is connected to the current balancing unit  220  and the control unit  240 , detects a current flowing the current balancing unit  220  and then outputs a voltage-type detection signal P corresponding to the detected current. 
   The first to third antenna sections S 1  to S 3  of the detection unit  230  are connected to the first to third voltage dividing sections  231  to  233 , respectively, and are positioned adjacent to the respective contacts between the primary and secondary sides of the first to third transformers T 1  to T 3  so as to detect currents flowing in the first to third transformers T 1  to T 3  through electromagnetic induction. 
   In this case, since the first to third antenna sections S 1  to S 3  detect currents flowing in the first to third transformers T 1  to T 3  through electromagnetic induction, the antenna sections can detect the currents in the form of voltage. 
   In particular, the first to third antenna sections S 1  to S 3  are not directly connected to the first to third transformers T 1  to T 3 , but are spaced at a predetermined distance from the first to third transformers T 1  to T 3 , respectively. Therefore, the insulation design is easily made. Further, the first to third antenna sections S 1  to S 3  can be formed in the lower side of positions where the first to third transformers T 1  to T 3  are mounted on a printed circuit board (not shown). Therefore, it is possible to reduce the volume of the power supply device. 
   The first to third antenna sections S 1  to S 3  may be positioned at positions adjacent to the connection line between the power supply unit  210  and the current balancing unit  220  so as to detect the driving voltages Vin output from the power supply unit  210 . 
   The first to third voltage dividing units  231  to  233  respectively have two resistors connected in series to each other. Further, the first to third voltage dividing units  231  to  233  are connected to the first to third antenna sections S 1  to S 3 , respectively, so as to divide the voltage detected by the first to third antenna sections S 1  to S 3 . 
   The first to third diodes D 1  to D 3  have anodes connected to the first to third voltage dividing units  231  to  233 , respectively, and cathodes connected to one end of the capacitor C 0 , and supply the voltages divided by the first to third voltage dividing units  231  to  233  to the capacitor C 0 . 
   The capacitor C 0  has one end connected to contacts between the cathodes of the first to third diodes D 1  to D 3  and the control unit  240  and the other end grounded so as to set the voltage applied through the first to third diodes D 1  to D 3  to a detection signal P to deliver to the control unit  240 . 
   When any one of the plurality of loads L 1  to L 6  is opened, a high current is momentarily applied to a transformer connected to the opened load, among the first to third transformers T 1  to T 3 . The detection unit  230  detects the current to output a high-voltage detection signal P. 
   The control unit  240 , which is connected to the detection unit  230  and the power supply unit  210 , receives the detection signal P from the detection unit  230  and then compares the detection signal P with a preset reference voltage. When the magnitude of the detection signal P is equal to that of the reference voltage, the control unit  240  judges that an overcurrent or overvoltage did not occur in the driving voltage Vin supplied to the plurality of loads L 1  to L 6  and the loads L 1  to L 6  were not short-circuited or opened (normal state). Then, the control unit  240  outputs a control signal S 0  for driving the power supply unit  210  in a current state, thereby controlling the power supply unit  210 . 
   When the magnitude of the detection signal P is not equal to that of the reference voltage, that is, when the magnitude of the detection signal P is larger or smaller than that of the reference voltage, the control unit  240  judges that an overcurrent or overvoltage occurred in the driving voltages Vin or the plurality of loads L 1  to L 6  were short-circuited or opened. Then, the control unit  240  outputs a control signal S 0  for stopping the power supply unit  210 . Therefore, it is possible to prevent the damage of the power supply device caused by the overcurrent or overvoltage and the short-circuit or open state. 
     FIG. 3  is a circuit diagram of a power supply device according to a modification of the first embodiment of the invention. As shown in  FIG. 3 , the power supply device according to the modification of the first embodiment of the invention includes a power supply unit  210 , a current balancing unit  220 , a detection unit  230 , and a control unit  240  and drives a plurality of loads L 1  to L 6 . 
   The current balancing unit  220  is not connected to the high-voltage side of the power supply unit  210 , but is connected to the low-voltage side of the plurality of loads L 1  to L 6  so as to balance currents flowing in the loads L 1  to L 6 . 
   In the power supply device according to the modification of the first embodiment of the invention, the current balancing unit  220  is composed of first to third transformers T 1  to T 3  having primary, secondary, and tertiary sides, similar to the first embodiment. Therefore, the number of transformers can be reduced, which makes it possible to reduce the size of the power supply device. 
   Further, since the detection unit  230  detects the currents flowing through the plurality of loads L 1  to L 6  through electromagnetic induction, the insulation design is easily achieved. Further, as antenna sections S 1  to S 3  are mounted within a printed circuit board, the size of the power supply device can be reduced. 
   Second Embodiment 
   Hereinafter, a power supply device according to a second embodiment of the invention will be described with reference to  FIGS. 4 and 5 . The descriptions of the same components of the second embodiment as those of the first embodiment will be omitted. 
     FIG. 4  is a circuit diagram of a power supply device according to the second embodiment of the invention. 
   As shown in  FIG. 4 , the power supply device according to the second embodiment of the invention includes a power supply unit  310 , a current balancing unit  320 , a detection unit  330 , and a control unit  340  and drives a plurality of loads L 1  to L 6  with constant brightness. 
   The current balancing unit  320  is composed of transformers T 1  to T 6  of which the number is equal to the number of the loads L 1  to L 6 . Each of the transformers T 1  to T 6  has a primary side and a secondary side. 
   The primary sides of the transformers T 1  to T 6  are connected to the power supply unit  310 . The primary sides of the transformers T 1  to T 6  receive a driving voltage Vin supplied from the power supply unit  310  and then supply the driving voltage Vin to the loads L 1  to L 6 , respectively, so as to induce the driving voltage Vin to the secondary sides. 
   The secondary sides of the transformers T 1  to T 6  are connected in series to each other so as to balance currents corresponding to the driving voltages Vin induced from the primary sides, respectively. Accordingly, the plurality of transformers T 1  to T 6  of the current balancing unit  320  can balance the currents i 1  to i 6  corresponding to the driving voltages Vin supplied to the plurality of loads L 1  to L 6 . 
   The detection unit  330  includes a plurality of antenna sections S 1  to S 3  spaced at a predetermined distance from the transformers T 1  to T 6 , a plurality of voltage dividing sections  331  to  333 , first to third diodes D 1  to D 3 , and a capacitor C 0 . 
   The detection unit  330  configured in such a manner detects a current flowing in the secondary sides of the transformers T 1  to T 6  through the first to third antenna sections S 1  to S 3  by using electromagnetic induction and then outputs a detection signal P corresponding to the current. 
   Then, as the control unit  340  receives the detection signal P to judge whether the plurality of loads L 1  to L 6  are opened or short-circuited or not, the control unit  340  can control the power supply unit  310 . Therefore, it is possible to prevent the damage of the power supply device. 
   In the power supply device according to the second embodiment of the invention, the first to third antenna sections S 1  to S 3  of the detection unit  330  are not directly connected to the secondary sides of the transformers T 1  to T 6 , but detect the currents flowing in the transformers T 1  to T 6  through the electromagnetic induction. Therefore, the insulation design for the transformers T 1  to T 6  is easily achieved. Accordingly, it is easily to configure a power supply device for driving loads which require a high voltage. 
     FIG. 5  is a circuit diagram of a power supply device according to a modification of the second embodiment of the invention. As shown in  FIG. 5 , the power supply device according to the modification of the second embodiment of the invention has a configuration that the current balancing unit  320  and the detection unit  330  are connected to a low voltage side of the loads without receiving the driving voltage Vin of the power supply unit  310 . 
   Accordingly, the current balancing unit  330  receives currents flowing through the plurality of loads L 1  to L 6  and then balances the currents i 1  to i 6 . Further, the detection unit  330  detects the current balanced by the current balancing unit  320  through electromagnetic induction. Therefore, the detection unit  330  can judge the abnormalities of the loads L 1  to L 6 , that is, whether the loads L 1  to L 6  are opened or short-circuited or not. 
   Further, one antenna section may be provided to each of the transformers T 1  to T 6  so as to detect a current flowing in the current balancing unit  330 . 
   Meanwhile, in the power supply device according to the first and second embodiments of the invention, the configuration for driving six loads L 1  to L 6  has been described, but is only an example for the detailed descriptions. The number of loads is not limited thereto. 
   According to the present invention, the current balancing unit is composed of the transformers having the primary, secondary, and tertiary sides. Therefore, it is possible to reduce the volume of the power supply device. 
   Further, the detection unit is not directly connected to the transformers, but detects currents flowing in the current balancing unit through the electromagnetic induction. Therefore, the insulation design of the transformer can be easily achieved. 
   Although a few embodiments of the present general inventive concept have been shown and described, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the general inventive concept, the scope of which is defined in the appended claims and their equivalents.