Abstract:
The present invention is disclosed a piezoelectric transformer with multiple outputs for lighting a plurality of cold cathode fluorescent lamps at the same time by forming a plurality of output electrodes as one body and a stabilizer having the piezoelectric transformer with multiple output electrodes. The piezoelectric transformer includes a piezoelectric plate; an input electrode formed on an upper surface of the plate; a plurality of output electrodes having an identical band shape, arranged in equal distance in the longitudinal direction of the plate at an outer side of the input electrode, and connected electrically to one ends of the plurality of the cold cathode fluorescent lamps respectively; and a common electrode formed on a bottom surface of the plate, confronting to the input electrode, commonly connected to ground of the stabilizer and other ends of the plurality of the cold cathode fluorescent lamps.

Description:
This application is a divisional of U.S. patent application Ser. No. 09/894,452 filed on Jun. 28, 2001, which is hereby incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to Rosen type Piezoelectric Transformer constituting a stabilizer for cold cathode fluorescent lamp being used for back light of liquid crystal display (LCD) device, more particularly, to a Rosen type Piezoelectric Transformer with multiple output electrodes for lighting a plurality of cold cathode fluorescent lamp at the same time by forming multiple output electrodes as one body and a stabilizer for multiple light source using that. 
     2. Description of the Prior Art 
     As well known to those skilled in the art, a fluorescent lamp needs high voltage at initial lighting in order to emit required thermal electrons for an electric discharge. And, after electric discharge, the voltage impressed on the fluorescent lamp has negative resistance characteristics reduced when lamp current increases. 
     Especially, a cold cathode fluorescent lamp being used for backlight of liquid crystal display (LCD) device is light source using cold emission (electron emission caused by forcing strong electric field to cathode surface). In order to light the Backlight comprised of the cold cathode fluorescent lamp, it needs about 500 V need. And, generally, a step-up transformer is used for convert the commercial AC power source to the driving voltage. 
     The stabilizer is a lamp lighting device applying the driving voltage for lighting on the fluorescent lamp with properties mentioned above, and comprises, as shown in FIG. 6, rectifying section  621  which rectifies AC commercial source  61  to DC voltage in some level, power factor compensation section  622  compensating for the power factor caused by the fluctuation of AC commercial voltage source in respect of the output voltage of the rectifying section  621 , AC voltage generating section  623  converting the DC voltage inputted through the power factor compensation section  622  to proposed AC voltage of high frequency, and a resonating section  624  for resonating with the output voltage of a AC voltage generating section  623  and supplying the AC voltage on the fluorescent lamp  63 . 
     As above-mentioned, AC voltage generating section  623  is called an inverter. 
     And, said resonating section  624  is conventionally constructed to generate the resonance by the inductance of the winding type transformer and the capacitance of a resonance capacitor with connection of the winding type transformer. But the winding type transformer has some problems that the rate of producing poor quality is high and the credibility of the stabilizer is reduced because the deviation of the quality of core is excessive, so said winding type transformer is recently replaced with a piezoelectric transformer such that the resonance is generated by the inductance of the inductor with the capacitance of the piezoelectric transformer. 
     But the above statement is the case of connecting one fluorescent lamp to one stabilizer. On the other hand, in case of lighting more than two fluorescent lamps by connecting the fluorescent lamps into one stabilizer, if one of numerous fluorescent lamps is lighted, other fluorescent lamps connected to the wound-type transformer in parallel is not lighted because a lower voltage is supplied to the other fluorescent lamps by lighting the one fluorescent lamp. 
     Accordingly, in the case of connecting two or more fluorescent lamps to the one stabilizer, as shown in FIGS. 8 and 9, the ballast capacitor is directly connected between fluorescent lamps  72 ,  82  and transformers  712 ,  812  such that the voltage required for initial lightening is impressed on the fluorescent lamp even if a certain fluorescent lamp is lighted ahead. 
     Hence, the conventional stabilizer used for a plurality of light sources is constructed as shown in FIGS. 8 and 9. 
     As shown in FIG. 8, the stabilizer comprises a circuit section  711 , which includes the rectifying section  621 , the power compensating section  622 , the AC voltage generating section  623 , and the resonance capacitor of the resonating section  624 , the piezoelectric transformer  712  of which input electrode is connected to the resonance capacitor of the circuit section  711 , and a plurality of ballast capacitors  713  being connected to output electrode of the piezoelectric transformer  712  in parallel. Wherein the number of ballast capacitors is same that of lamps. Furthermore, a plurality of fluorescent lamps  72  is connected to other terminal of the plurality of ballast capacitors  713  of the stabilizer  71  respectively. 
     As shown in FIG. 9, the stabilizer for a plurality of fluorescent lamps having a wound-type transformer comprises a circuit section  811 , which includes the rectifying section  621 , the power compensating section  622 , the AC voltage generating section  623 , and the resonance capacitor of the resonating section  624 . And the stabilizer comprises the wound-type transformer  812  of which input electrode is connected to a resonance capacitor of the circuit section  811 , and a plurality of ballast capacitors  813  being connected to output electrode of the wound-type transformer  812  in parallel. Furthermore, the plurality of fluorescent lamps  82  is connected to other terminal of the plurality of ballast capacitors  713  of the stabilizer  71  respectively. 
     In the stabilizer above, because AC voltage supplied by the wound-type transformer  712  or the piezoelectric transformer  812  is divided equally among the plurality of fluorescent lamps via the ballast capacitor  713 , 813 , the plurality of fluorescent lamps can be lighted at the same time. Wherein the ballast capacitor  713 , 813  has a high withstand voltage characteristic, and its size is also big. 
     Accordingly, as shown in FIG. 7 or FIG. 8, because the stabilizer needs the ballast capacitors in proportion to the number of the connected fluorescent lamp, a volume and the number of components increase, and a cost increases also. 
     Thus, in the case of constituting a stabilizer as mentioned above, there have been some problems that numbers of components and the volume increase and the production cost rise because a ballast capacitor is required proportion to numbers of connected fluorescent lamp. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of the present invention is to provide a Rosen type piezoelectric transformer having a plurality of output electrodes with uniform output property which makes the fluorescent lamp light stably, the operation be simple, and the cost be reduced. The present invention provides a Rosen type Piezoelectric Transformer with multiple output electrodes, being used for a stabilizer to light a plurality of cold cathode fluorescent lamps, comprising: a piezoelectric plate; an input electrode formed at an upper surface of the plate; a plurality of output electrodes having an identical band shape, arranged in equal distance in the longitudinal direction of the plate at an outer side of the input electrode, and connected electrically to one ends of the plurality of the cold cathode fluorescent lamps respectively; and a common electrode formed at a bottom surface of the plate, confronting to the input electrode, commonly connected to ground of the stabilizer and other ends of the plurality of the cold cathode fluorescent lamps. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, 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 shows a perspective view of a stabilizer for a plurality of lamps having a Rosen type Piezoelectric Transformer in accordance with the primary embodiment of the present invention; 
     FIG. 2 shows a perspective view of the Piezoelectric Transformer in accordance with the present invention in FIG. 1; 
     FIG. 3 shows a perspective view of a Rosen type Piezoelectric Transformer in accordance with another embodiment of the present invention and a stabilizer for lighting four lamps; 
     FIG. 4 shows a perspective view of the modified Piezoelectric Transformer as shown in FIG. 3; 
     FIG. 5 shows a perspective view of a Rosen type Piezoelectric Transformer in accordance with another embodiment of the present invention and a stabilizer for a plurality of lamps applying that; 
     FIG. 6 shows a perspective view of the modified Piezoelectric Transformer as shown in FIG. 5; 
     FIG. 7 shows a block diagram of a conventional fluorescent lamp stabilizer; 
     FIG. 8 shows a perspective view of a stabilizer for a plurality of lamps applying a conventional winding type piezoelectric transformer; and 
     FIG. 9 shows a perspective view of a stabilizer for a plurality of lamps applying a conventional piezoelectric transformer. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference now should be made to the drawings, in which the same reference numerals are used throughout the different drawings to designate the same or similar components. 
     FIG. 1 shows a view of an embodiment of a piezoelectric transformer and a stabilizer using the piezoelectric transformer, in this embodiment the 2 light sources is used. 
     As shown in FIG. 1, a Rozen type piezoelectric transformer  10  comprises an input electrode  3  formed at the center of the upper surface of the piezoelectric plate  1  in the longitudinal direction of the plate and connected to a circuit section  2  of a stabilizer  100 , a common electrode  7  formed on the bottom surface of the piezoelectric plate  1  opposed to the input electrode  3 , and two output electrodes  6  formed on the both confronting side surface in the longitudinal direction of the plate  1 . 
     And, the input electrode  3  and the common electrode  7  are connected to an output of the circuit section  2  in the stabilizer  100 , the two output electrode  6  is respectively connected to one ends of two cold cathode fluorescent lamps  4  of a lamp section  200 , and the other ends of two cold cathode fluorescent lamps  4  is connected to the common electrode  7 . That is, two cold cathode fluorescent lamps  4  are connected to the piezoelectric transformer  10  in parallel. 
     As described above, the circuit section  2  converts the commercial voltage source of 220 V or 110 V with AC voltage of a predetermined voltage level and frequency. And then the AC voltage is impressed the input electrode  3  and the common electrode  7 . As result, it brings about a longitudinal vibration. The longitudinal vibration is transmitted the output electrodes  6 , and then a AC voltage outputs between the output electrodes  6  and the common electrode  7 . The AC voltage outputted the output electrodes  6  is related to the distance to the input electrode  3  and the thickness of the piezoelectric plate  1 , and the output electrodes  6  placed on the confronting side surface has the same output property because each of the output electrodes  6  has the same condition. Thus, the uniform voltage is impressed to two cold cathode fluorescent lamps  4  such that all of the fluorescent lamp  4  can be lighted. 
     FIG. 2 shows a perspective view of the modified Piezoelectric Transformer as shown in FIG.  1 . The piezoelectric transformer is made by multi-layering first piezo-sheet  8  printing the input electrode  3  on the surface and second piezo-sheet  8 ′ printing the common electrode  7  on the surface in turns. The input electrodes  3  on first piezo-sheet  8  is connected each other and the common electrode  7   s  on second piezo-sheet  8 ′ is connected each other. 
     FIGS. 3 and 4 show perspective views of a Piezoelectric Transformer in accordance with an embodiment of the present invention and a stabilizer for 4 light sources applying that. 
     As shown in the drawings, the piezoelectric transformer has an input electrode  3  formed at the center of the upper surface of the piezoelectric plate  1  in the direction of its width. 
     In multi-layer type, the input electrode  3  and the output electrodes  6  is formed on the surface of a piezo-sheet. The input electrode  3  is connected to the circuit section  2 . 
     And, Four output electrodes  6  is formed to the positions divided into equal distance on the upper surface and the both confronting side surface in longitudinal direction. And the common electrode  7  is formed on a the bottom surface of the piezoelectric plate  1  opposed to the input electrode  3 . 
     The input electrode  3  is connected to the output of generating AC voltage of the circuit section  2 . The four output electrodes  6  are connected to the one ends  5 A of the cold cathode fluorescent lamps  4 . And the other ends  5 B of the cold cathode fluorescent lamps  4  and the ground of the circuit section  2  are connected to the common electrode  7 . Additionally, FIGS. 5 and 6 show perspective views of a piezoelectric transformer in accordance with another embodiment of the present invention. In FIG. 5, an input electrode  3  is formed at one end of the upper surface of the plate  1  in the longitudinal direction of the piezoelectric plate  1 , and connected to the circuit section  2 . The output electrodes  6  is formed on a side surface of the piezoelectric plate  1  in a direction of thickness of the plate and is formed on a upper surface in a band shape, being arranged in an equal distance. And, the common electrode  7  is formed on the bottom surface of the piezoelectric plate  1  opposed to the input electrode  3  and is connected to the AC voltage generator  2  and the other ends  5 B of the plurality of the cold cathode fluorescent lamps  4  at the same time. 
     In FIG. 6, the input electrode  3  connected to the circuit section  2  and the output electrodes  6  is formed on the surface of a piezo-sheet, and the common electrode  7  is formed on the surface of the other piezo-sheet. And a piezo-sheet formed the input electrode  3  and output electrods  6 , and the other piezo-sheet formed the common electrode  7  is layered in turns. 
     The operational effect of the present invention will be described herein below. 
     In order to satisfy restricting the noise, lowering the spending power, making the device miniaturization, and the like, a piezoelectric transformer having the piezoelectric effect is used. 
     The basic principle of the piezoelectric transformer is the following. A deformation of another section of the piezoelectric transformer is generated due to a deformation generated by impressing a voltage to one section of the piezoelectric transformer, and a second voltage is then generated on another section. The principle above is applied to the Rosen type, which is the simplest type. 
     A piezoelectric plate is formed by stacking a plurality of sheets to which internal electrodes is printed in some patterns and stacked, an external input electrode is formed on one longitudinal side of upper and bottom surface of the piezoelectric plate, and an output electrode is formed at a confronting position of the input section on the side of the piezoelectric plate. 
     If the voltage having resonance frequency is impressed to the external output electrode, a longitudinal vibration mode is generated in the internal electrode, and the longitudinal vibration is generated in the output electrode formed on the side surface of the piezoelectric plate by the generated longitudinal vibration mode, and the voltage is generated in the output electrode as a piezoelectric effect occurred by the produced stress. And then the voltages of the output terminal rise. 
     As shown in the FIGS. 1 and 2, the input electrode  3  and the common electrode  7  formed on the upper and bottom surface of the piezoelectric plate  1  are connected to the AC voltage generator  2 . If a voltage having a resonance frequency from the AC voltage generator  2  is supplied to the input electrode  3  and the common electrode  7 , the output electrode  6  formed on both side of the piezoelectric plate  1  vibrates is generated in a direction of length by longitudinal vibration mode. 
     A voltage is applied to the output electrode  6  by the piezoelectric effect produced by the stress of the piezoelectric plate  1 , and a high voltage is impressed on the cold cathode fluorescent lamp  4  connected through the terminal  5 A. 
     And the same voltage is impressed through the common electrode  7  placed in the bottom surface of the piezoelectric plate  1 , which is formed at confronting position of the input electrode  3 , and the common electrode  7  is connected to the AC voltage generator  2  and the other terminals  5 B of a plurality of the cold cathode fluorescent lamps  4  such that the cold cathode lamp  4  is impressed a high voltage. 
     In addition, as shown in the FIGS. 3 and 4, the resonance frequency is impressed by means of inputting the input electrode  3  and the common electrode  7  placed in the upper and bottom surface of the piezoelectric plate  1  or made from stacking into the AC voltage generator  2 . Then the longitudinal vibration mode occurs in the internal section, and this makes the longitudinal vibration in the direction of length of the multiple output electrodes  6  placed on the both surface of the piezoelectric plate  1  and the surface of the input electrode  3 . 
     A voltage is applied to the output electrode  6  by the piezoelectric effect produced by the stress, and boosting is produced to impress high voltage on the cold cathode fluorescent lamp  4  connected through the terminal  5 A. 
     And the same voltage is impressed through the common electrode  7  placed on the bottom surface of the piezoelectric plate  1 , which is formed at confronting position of the input electrode  3 , and the common electrode  7  is connected to the AC voltage generator  2  and the other terminals  5 B of a plurality of the cold cathode fluorescent lamps  4  such that the cold cathode lamp  4  is impressed a high voltage. 
     Accordingly, it is possible to reduce the number of the components and minimize the size of the inverter by using the piezoelectric transformer with multiple outputs of the present invention, and this removes the retraction of designing and the needs of installation of high internal voltage condenser, an additional grounding equipment is also unnecessary. 
     Accordingly, it is possible to generate a multiple output voltage having an uniform output property by using the multiple output electrodes. Thus, by providing a cold cathode fluorescent lamp using the piezoelectric transformer with multiple outputs, a easy working and a cost savings may be realized without an additional ballast capacitor. 
     Finally, by minimizing a volume of stabilizer, a design restriction of the stabilizer may be lower, and it is not necessary to design about the isolation additionally. 
     In addition, multiple outputs are easily obtained by applying the piezoelectric transformer of the present invention and various vibration modes (including length type, width type, area type, radial type, ring type vibration mode, and the like) to a power converting circuit (for example, DC-DC converter, AC-DC converter, DC-AC converter) transmitting a power. 
     Although various embodiments of this invention have been shown and described, it should be understood that variations, modifications and substitutions, as well as rearrangements and combinations of the preceding embodiments can be made by those skilled in the art without departing from the novel spirit and scope of this invention.