Abstract:
There are provided a current balance circuit having a protection function that prevents the current balance circuit from being damaged during a preset time period by maintaining a constant level of power being supplied to the lamp, and a power supply. The current balance circuit having the protection function includes a current balance unit maintaining current balance of lamp driving power supplied to a lamp unit including a plurality of lamps, and a protection unit detecting the lamp driving power supplied to the lamp unit from the current balance unit, cutting-off the lamp driving power after a preset time period when the lamp operates abnormally, and controlling a voltage level of the lamp driving power to a preset reference voltage level or lower during the preset time period.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority of Korean Patent Application No. 10-2009-0078755 filed on Aug. 25, 2009, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a current balance circuit and a power supply, and more particularly, to a current balance circuit having a protection function that protects a device by detecting an abnormal lamp operation after a predetermined time period in order to ensure a normal lamp operation, and further having a protection function that prevents the current balance circuit from being damaged during the preset time period by maintaining a constant level of power, being supplied to the lamp, and a power supply including the same. 
     2. Description of the Related Art 
     Recently, much attention has been drawn to liquid crystal display (LCD) devices that are smaller and lighter than existing display devices. 
     An LCD device necessarily employs a backlight unit that emits light. In addition, the LCD device may be provided with a power supply to supply power to lamps of the backlight unit. 
     The power supply may include a power supply circuit supplying power to lamps, and a current balance circuit maintaining the current balance of power being supplied to the lamps. 
     The current balance circuit may have a protection function that prevents device breakdown caused by an abnormal lamp operation such as an open lamp. 
     After a backlight unit having the above configuration is manufactured, commercial power is supplied to this backlight unit to check whether or not it is operating normally. To this end, the protection function of a current balance circuit is performed after a predetermined time period. 
     For a reduction in manufacturing costs, a current balance circuit, which had formerly been employed at each end of a lamp, is currently employed only at a single end of a lamp. Thus, the level of a voltage applied to the coil of the current balance circuit has been doubled compared to that of existing examples. For this reason, under the open-lamp condition, the coil may be burnt out due to the overvoltage applied to the coil. 
     SUMMARY OF THE INVENTION 
     An aspect of the present invention provides a current balance circuit having a protection function that protects a device by detecting an abnormal lamp operation after a predetermined time period in order to ensure a normal lamp operation, and further having a protection function that prevents the current balance circuit from being damaged during the preset time period by maintaining a constant level of power, being supplied to the lamp, and a power supply including the same. 
     According to an aspect of the present invention, there is provided a current balance circuit having a protection function, the current balance circuit including: a current balance unit maintaining current balance of lamp driving power supplied to a lamp unit including a plurality of lamps; and a protection unit detecting the lamp driving power supplied to the lamp unit from the current balance unit, cutting-off the lamp driving power after a preset time period when the lamp operates abnormally, and controlling a voltage level of the lamp driving power to a preset reference voltage level or lower during the preset time period. 
     The current balance unit may include a plurality of current balancing transformers corresponding with the plurality of lamps on a one-to-one basis and maintaining the current balance of the lamp driving power, the current balancing transformers each including: a primary winding receiving the lamp driving power and sending the received lamp driving power to a corresponding lamp among the plurality of lamps; and a secondary winding electromagnetically coupled with the primary winding and electrically connected to an adjacent current balancing transformer among the plurality of current balancing transformers to form at least one loop and maintain current balance. 
     The protection unit may include: a detection part detecting power induced from the secondary winding of the current balancing transformer; a delay transmission part delaying a detected voltage from the detection part by the preset time period and sending the delayed voltage to the outside; and a regulation part receiving the detected voltage from the detection part and regulating a voltage level of the lamp driving power to a preset voltage level during the preset time period. 
     The detection part may include: a plurality of tertiary windings included in the plurality of current balancing transformers and inducing and receiving power from the respective secondary windings; and a diode group rectifying power from each of the plurality of tertiary windings. 
     The delay transmission part may include: a comparator comparing the detected voltage with a preset reference voltage; and a delay delaying a comparison result from the comparator by the preset time period and outputting the delayed comparison result. 
     The regulation part may include: a diode rectifying the detected voltage; a resistor reducing a voltage from the diode; a capacitor charged with the voltage from the resistor; and a discharge resistor discharging the voltage charged in the capacitor. 
     According to another aspect of the present invention, there is provided a power supply having a protection function, the power supply including: a power supply circuit converting commercial alternating current (AC) power into preset lamp driving power and supplying the lamp driving power to a lamp unit including a plurality of lamps; and a current balance circuit including: a current balance unit maintaining the current balance of a lamp driving power being supplied from the power supply circuit to each of the plurality of lamps; and a protection unit detecting the lamp driving power supplied to the lamp unit from the current balance unit, cutting off the lamp driving power after a preset time period when the lamp operates abnormally, and controlling a voltage level of the lamp driving power to a preset reference voltage level or lower during the preset time period. 
     The power supply circuit may include: a rectification unit rectifying and smoothing commercial AC power; a power factor correction unit correcting a power factor of the rectified power from the rectification unit; an inverter unit switching the corrected power from the power factor correction unit; a transformer unit transforming the switched power from the inverter unit into the lamp driving power; and a control unit controlling a switching operation of the inverter unit according to a signal from the protection unit. 
     The control unit may adjust an ON/OFF duty of the inverter unit according to a control signal from the protection unit, and cut-off the switching operation of the inverter unit according to a cut-off signal from the protection unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a schematic view illustrating the configuration of a power supply according to an exemplary embodiment of the present invention; 
         FIG. 2  is a schematic view illustrating a current balance circuit used in a power supply according to an exemplary embodiment of the present invention; and 
         FIG. 3  is a signal graph of a current balance circuit used in a power supply according to an exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. 
       FIG. 1  is a schematic view illustrating the configuration of a power supply according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 1 , a power supply  100 , according to this embodiment, may include a power supply circuit  110  and a current balance circuit  120 . 
     The power supply circuit  110  may include a rectification unit  111 , a power factor correction unit  112 , an inverter unit  113 , a transformer unit  114  and a control unit  115 . 
     The rectification unit  111  may rectify and smooth commercial alternating current (AC) power. 
     The power factor correction unit  112  may correct a power factor by adjusting a phase difference between the current and voltage of rectified power from the rectification unit  111 . 
     The inverter unit  113  converts power by switching the corrected power from the power factor correction unit  112 . 
     The transformer unit  114  supplies lamp driving power to lamps by transforming switched power from the inverter unit  113  according to a preset turns ratio. 
     The control unit  115  may control the switching operation of the inverter unit  113  according to a feedback signal FB of the lamp driving power supplied to lamps, and a control signal VR and a cut-off signal OVP from the current balance circuit  120 . The control unit  115  may adjust an ON/OFF duty of the inverter unit  113  according to the control signal VR from the current balance circuit  120 , and stop the switching operation of the inverter unit  113  according to the cut-off signal OVP from the current balance circuit  120 . 
     The current balance circuit  120  may include a current balance unit  121 , and a protection unit  122 . 
     The current balance unit  121  may maintain the current balance of the lamp driving power sent from the power supply circuit  110  to each lamp of a lamp unit. 
     The protection unit  122  may include a detection part  122   a  detecting the voltage of lamp driving power sent from the current balance unit  121  to each lamp, a delay transmission part  122   b  delaying a detection result obtained by the detection part  122   a  by a preset time period and transmitting a cut-off signal OVP after the preset time period, and a regulation part  122   c  transmitting a control signal VR to the control unit  115  according to the detection result from the detection part  122   a  so that the lamp driving power has a preset voltage level during the preset time period. 
       FIG. 2  is a schematic view illustrating the configuration of a current balance circuit used in the power supply according to an exemplary embodiment of the present invention. 
     Referring to  FIGS. 1 and 2 , the current balance unit  121  of the current balance circuit  120  may include a plurality of current balancing transformers corresponding to lamps on a one-to-one basis. The plurality of current balancing transformers may each have a primary winding N 1  and a secondary winding N 2 . 
     The primary winding N 1  receives lamp driving power from the transformer unit  114 , and transmits the lamp driving power to each lamp. 
     The secondary winding N 2  is electromagnetically coupled with the primary winding N 1  to thereby form the current balancing transformer. The secondary winding N 2  induces and receives the lamp driving power according to a turns ratio with the primary winding N 1 . The respective secondary windings N 2  of the current balancing transformers are electrically connected to each other and form at least one loop, thereby maintaining a current balance state. The induced power may be provided to the control unit  115  as a feedback signal FB. 
     The protection unit  122  may include the detection part  122   a , the delay transmission part  122   b  and the regulation part  122   c.    
     The detection part  122   a  may include a plurality of tertiary windings N 3  and a diode group D. 
     The plurality of tertiary windings N 3  correspond to the primary and secondary windings N 1  and N 2  on a one-to-one basis, and are electromagnetically coupled with the corresponding primary and secondary windings N 2 , respectively, thereby forming the current balancing transformers. Accordingly, each tertiary winding N 3  induces and receives power from the corresponding secondary winding N 2  according to each turns ratio, and thus detects the voltage level of the lamp driving power. 
     The diode group D includes a plurality of diodes respectively corresponding to the tertiary windings N 3 , and rectifies the detected voltage from the tertiary windings N 3 . 
     The delay transmission part  122   b  may include a comparator OP 1  comparing the detected voltage with a preset reference voltage, and a delay delaying the comparison result from the comparator OP 1  by the preset time period and outputting the delayed comparison result. 
     First, the comparator OP 1  compares the detected voltage having a level regulated by a regulation circuit RC with the voltage level of reference voltage set via a reference voltage circuit RVC. 
     The delay delays the comparison result from the comparator OP 1  by a preset time period and outputs the delayed comparison result. Thus, the delay may include a capacitor C and a resistor R delaying the comparison result according to a set time constant, and a buffer OP 2  outputting the delayed comparison result. 
     Accordingly, when the detected voltage has a higher level than the reference voltage, namely, when an abnormal operation such as an open-lamp occurs, the delay transmission part  122   b  may transmit a cut-off signal OVP to the control unit  115  after the predetermined time period. 
     Even if an abnormal operation such as an open-lamp may occur during this predetermined time period, the switching operation of the inverter unit  113  may be cut-off after the predetermined time period so that the overall operation of a backlight unit can be checked. Therefore, in order to protect components such as the winding of the current balancing transformer against the abnormal operation occurring during the predetermined time period, the regulation part  122   c  regulates the switching duty of the inverter unit  113  so as to cause the voltage level of the lamp driving power, being sent to each lamp, to be constant. 
     Namely, the regulation part  122   c  may include a diode D 1 , a resistor R 1 , a capacitor C 1  and a discharge resistor R 2 . The diode D 1  rectifies the detected voltage from the detection part  122   a , reduces the rectified voltage according to a resistance value, the capacitor C 1  is charged with the reduced voltage, and the discharge resistor R 2  discharges the voltage charged in the capacitor C 1 . 
     Accordingly, the regulation part  122   c  charges/discharges the detected voltage to thereby output a control signal VR having an AC voltage. This is because the switching operation of the inverter unit  113  is stopped when a DC voltage having a constant level is applied to the input port of the control unit  115 . 
     In detail, the cut-off signal OVP from the delay transmission part  122   b  and the control signal VR from the regulation part  122   c  are sent to the same output port of the control unit  115 . Then, the control unit  115  accordingly sends a switching signal SS to the inverter unit  113 . When the signal received via the input port is a DC signal, the control unit  115  outputs a switching signal for cutting-off the switching operation of the inverter unit  113 . When the received signal is an AC signal, the switching signal output from the control unit  115  regulates the switching duty of the inverter unit  113  according to the received AC signal. 
       FIG. 3  is a signal graph of the current balance circuit applied to a power supply according to an exemplary embodiment of the present invention. 
     Referring to  FIGS. 1 through 3 , the regulation part  122   c  of the current balance circuit  120 , applied to the power supply  100  of the present invention, sends a control signal VR, an AC signal, to the control unit  115  in order to protect the winding of the current balance unit  121  during the predetermined time period t 1  from an abnormal operation such as an open-lamp condition. In the case of the abnormal operation, the regulation part  122   c  sends a cut-off signal OVP to the control unit  115  after the predetermined time period t 1  during which the backlight unit is checked. 
     As described above, the current balance circuit, having a protection function for protecting a device by detecting an abnormal lamp operation after a predetermined time in order to ensure a normal operation of lamps, can be prevented from being damaged during the predetermined time period. 
     As set forth above, according to exemplary embodiments of the invention, the current balance circuit having a protection function for protecting a device by detecting an abnormal lamp operation after a predetermined time period can be prevented from being damaged during the predetermined time period. 
     While the present invention has been shown and described in connection with the exemplary embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.