200814855 九、發明說明： 【發明所屬之技術領域】 |發明是有關於-種用以將直流電壓轉換為交流電壓 m轉換器’且㈣是㈣於—種冷陰極螢光燈管（c〇id Cathode FlU0rescent Lamp ’ CCFL)之電源轉換器。 【先前技術】200814855 IX. Description of the invention: [Technical field to which the invention pertains] | The invention relates to a converter for converting a direct current voltage into an alternating voltage m' and (d) is a (four) cold cathode fluorescent lamp (c〇id) Cathode FlU0rescent Lamp 'CCFL) power converter. [Prior Art]
一般而言，常見的液晶顯示器有二種，一種是反射式， 而另-種為穿透式。在穿透式的液晶顯示器中，通常需要 使用到背光源，且一般係使用冷陰極螢光燈管（ccfl)作為 其背光源，其優點諸如：高發光效率、使用週期長…等等。 然而，由於冷陰極螢光燈管的電源轉換器通常都包含二或 多個電晶體，所以其電源轉換器—般均具有設計複雜且不 易製造的問題，致使無法有效地減少製造成本及時間。 口此，有必要提出一種簡易的電源轉換器，以減少其 製造成本及時間。 【發明内容】 依照本發明一實施例，提出一種電源轉換器，用以將 直流電壓轉換為交流電壓以供一發光源使用，並包含一驅 動電路、一開關、一變壓器以及一電容。開關具有用以耦 接於驅動電路之一控制端，以及用以耦接於一接地電壓之 一接地端。變壓器具有一 一次側以及一二次側，其中一次 側上之線圈係耦接於直流電壓以及開關之一信號端之間， 使得交流電壓產生於二次側。電容則是耦接於開關之接地 200814855 端以及信號端之間。 根據本發明上述之實施例可知，此電源轉換器較許多 已知的電源轉換器在設計上更為簡單，因此可有效地減少 其製造成本及製造時間。而且，此電源轉換器較一般而言 可更簡單地控制，以供冷陰極螢光燈管（CCFL)使用。 【實施方式】 請參照第1圖，係繪示依照本發明實施例之一種用於 冷陰極螢光燈管(CCFL)之電源轉換器的示意圖。此電源轉 換器100係用以將由直流（DC)電壓輸出電路102產生的直 流電壓轉換為一交流（AC)電壓，以供一冷陰極螢光燈管 (CCFL·) 104使用。電源轉換器10〇包括一驅動電路106、 一開關108、一變壓器11〇、一電容C1以及一去耦合電容 C2。開關108具有耦接於驅動電路1〇6之一控制端，以及 耦接於一接地電壓之一接地端。驅動電路106係用以輸出 一脈衝寬度調變（Pulse Width Modulation ’ PWM)信號以控 制開關108。變壓器110具有——次側以及一二次側。其 中，一次側上的線圈係耦接於直流電壓輸出電路1〇2以及 開關108之一信號端之間，藉以在二次側產生交流電壓。 電容C1係耦接於開關1〇8的接地端以及信號端之間，且可 與變壓器110相互作用，藉以決定電源轉換器1〇〇的諧振 頻率（Resonant Frequency)，並因而改善電源轉換器1 〇〇的 工作效率。去耦合電容C2則是耦接於變壓器110之二次侧 的一端，並輸出交流電壓供冷陰極螢光燈管104使用。此 外，去耦合電容C2以及變壓器110之二次側的另一端係分 200814855 別耦接於冷陰極螢光燈管104。 開關108可更包括一 N型金屬氧半導體場效電晶體 (Metal-Oxide-Semiconductor Field Effect Transistor MOSFET) Ml以及一二極體D1，其中二極體D1可為電晶 體Ml中之一體二極體（body diode)，或是與電晶體Μι並 聯之額外的二極體。電晶體Μ1的閘極係用以作為開關j 8 的控制端，並耦接於驅動電路106,其第一源汲極係用以作 為開關108的信號端，並耦接於變壓器11()之一次側線圈 的一端，而其第二源汲極則係用以作為開關1〇8的接地端， 並麵接於接地電壓。此外，二極體D1則係耦接於電晶體 Ml的第一源汲極和第二源汲極之間。 第2圖係緣示如第1圖所示之開關開啟時電源轉換器 操作的示意圖。第4A及4B圖係分別繪示變壓器的一次側 及二次側電壓的示意圖。請參照第2、4A及4B圖，當開 關1〇8(電晶體Ml)接收由驅動電路106輸出的信號而開啟 時’由直流電壓輸出電路102所輸出的電壓會使得變壓器 110的一次侧產生一正電壓VAB，因此電流II會經由變壓 斋u〇自直流電壓輸出電路102流至開關108，而電流12 也會在變壓器11〇的二次側產生，並流經去耦合電容C2， 此N*供冷陰極螢光燈管1 〇4使用的電壓vcd也會藉此產 生。除此之外，電流會由變壓器丨1()的一次側流至電容C卜 且電各C1會因此充電而使得其電壓隨時間增加。 第3圖係繪示如第1圖所示之開關關閉時電源轉換器 操作的示意圖。請參照第3、4A及4B圖，當開關108(電 晶體Ml)接收由驅動電路1〇6輸出的信號而關閉時，電容 200814855In general, there are two common types of liquid crystal displays, one is reflective, and the other is transmissive. In a transmissive liquid crystal display, a backlight is usually required, and a cold cathode fluorescent lamp (ccfl) is generally used as a backlight thereof, and advantages such as high luminous efficiency, long life cycle, and the like. However, since power converters for cold cathode fluorescent lamps usually contain two or more transistors, their power converters generally have problems of complicated design and are not easy to manufacture, so that manufacturing costs and time cannot be effectively reduced. To this end, it is necessary to propose a simple power converter to reduce its manufacturing cost and time. SUMMARY OF THE INVENTION According to an embodiment of the invention, a power converter is provided for converting a DC voltage into an AC voltage for use by an illumination source, and includes a driving circuit, a switch, a transformer, and a capacitor. The switch has a control end coupled to one of the drive circuits and a ground end coupled to a ground voltage. The transformer has a primary side and a secondary side, wherein the coil on the primary side is coupled between the DC voltage and one of the signal terminals of the switch such that an AC voltage is generated on the secondary side. The capacitor is coupled to the grounding of the switch at the end of the 200814855 and between the signal terminals. According to the above embodiment of the present invention, the power converter is simpler in design than many known power converters, thereby effectively reducing the manufacturing cost and manufacturing time. Moreover, this power converter can be more easily controlled for use with a cold cathode fluorescent lamp (CCFL). [Embodiment] Referring to Figure 1, there is shown a schematic diagram of a power converter for a cold cathode fluorescent lamp (CCFL) in accordance with an embodiment of the present invention. The power converter 100 is for converting a DC voltage generated by a direct current (DC) voltage output circuit 102 into an alternating current (AC) voltage for use by a cold cathode fluorescent lamp (CCFL) 104. The power converter 10A includes a driving circuit 106, a switch 108, a transformer 11A, a capacitor C1, and a decoupling capacitor C2. The switch 108 has a control end coupled to one of the drive circuits 1 and 6 and a ground coupled to a ground voltage. The drive circuit 106 is operative to output a Pulse Width Modulation 'PWM' signal to control the switch 108. The transformer 110 has a secondary side and a secondary side. The coil on the primary side is coupled between the DC voltage output circuit 1〇2 and one of the signal terminals of the switch 108 to generate an AC voltage on the secondary side. The capacitor C1 is coupled between the ground end of the switch 1〇8 and the signal end, and can interact with the transformer 110 to determine the resonant frequency of the power converter 1〇〇, and thus improve the power converter 1 Awkward work efficiency. The decoupling capacitor C2 is coupled to one end of the secondary side of the transformer 110 and outputs an AC voltage for use by the cold cathode fluorescent lamp 104. In addition, the decoupling capacitor C2 and the other end of the secondary side of the transformer 110 are coupled to the cold cathode fluorescent lamp 104 in 200814855. The switch 108 may further include a Metal-Oxide-Semiconductor Field Effect Transistor MOSFET M1 and a diode D1, wherein the diode D1 may be a body diode in the transistor M1. (body diode), or an additional diode in parallel with the transistor Μι. The gate of the transistor 用以1 is used as the control terminal of the switch j 8 and is coupled to the driving circuit 106. The first source drain is used as the signal terminal of the switch 108 and coupled to the transformer 11 () One end of the primary side coil and the second source drain are used as the grounding end of the switch 1〇8, and are connected to the ground voltage. In addition, the diode D1 is coupled between the first source drain and the second source drain of the transistor M1. Fig. 2 is a schematic diagram showing the operation of the power converter when the switch is turned on as shown in Fig. 1. Figures 4A and 4B are schematic diagrams showing the primary and secondary voltages of the transformer, respectively. Referring to FIGS. 2, 4A and 4B, when the switch 1〇8 (the transistor M1) receives the signal output from the drive circuit 106 and turns on, the voltage output by the DC voltage output circuit 102 causes the primary side of the transformer 110 to be generated. A positive voltage VAB, so the current II will flow from the DC voltage output circuit 102 to the switch 108 via the voltage change, and the current 12 will also be generated on the secondary side of the transformer 11〇 and flow through the decoupling capacitor C2. The voltage vcd used by the N* cold cathode fluorescent lamp 1 〇 4 is also generated by this. In addition to this, the current flows from the primary side of the transformer 丨1() to the capacitor Cb and the electric C1 is thus charged so that its voltage increases with time. Figure 3 is a schematic diagram showing the operation of the power converter when the switch is closed as shown in Figure 1. Referring to Figures 3, 4A and 4B, when the switch 108 (the transistor M1) receives the signal output from the drive circuit 1〇6, it is turned off, and the capacitor 200814855
Cl會放電’且變壓器110的一次侧會產生一負電壓vAB。 此時電流11會由電容C1流至變壓器11 〇的一次側，而電 流12也會在變壓器110的二次側產生，且供冷陰極螢光燈 官104使用的電壓Vcd也會精此產生。因此，變壓器1 1 〇 的電壓極性便可藉此交替轉換，且流經變壓器i丨〇之一次 側和二次側的電流11以及12的大小及方向亦可隨著時間作 改變。 由上述本發明之實施例可知，此電源轉換器較許多已 知的電源轉換器而言具有較少的電晶體，且在設計上更簡 單’所以可減少製造成本及時間。此外，此電源轉換器可 僅藉由一開關作控制，以將直流電壓轉換為交流電壓，因 此較一般而言可更簡易地控制，且更方便地供冷陰極螢光 燈管（CCFL)使用。 雖然本發明已以實施例揭露如上，然其並非用以限定 本發明，任何所屬技術領域中具有通常知識者，在不脫離 本發明之精神和範圍内，當可作各種之更動與潤飾，因此 本發明之保護範圍當視後附之申請專利範圍所界定者為 準〇 【圖式簡單說明】 為讓本發明之上述和其他目的、特徵、優點與實施例 能更明顯易懂，所附圖式之詳細說明如下： 第1圖係繪示依照本發明實施例之一種用於冷陰極螢 光燈管之電源轉換器的示意圖。 200814855 第2圖係繪示如第1圖所示之開關開啟時電源轉換器 操作的示意圖。 第3圖係繪示如第1圖所示之開關關閉時電源轉換器 操作的示意圖。 第4A圖係繪示變壓器的一次側電壓的示意圖。 第4B圖係繪示變壓器的二次側電壓的示意圖 【主要元件符號說明】 100 :電源轉換器 106 :驅動電路 102 :直流電壓輸出電路 108 :開關 104 :冷陰極螢光燈管 110 :變壓器Cl will discharge' and the primary side of transformer 110 will produce a negative voltage vAB. At this time, the current 11 flows from the capacitor C1 to the primary side of the transformer 11 ,, and the current 12 is also generated on the secondary side of the transformer 110, and the voltage Vcd used by the cold cathode fluorescent lamp 104 is also generated. Therefore, the voltage polarity of the transformer 1 1 〇 can be alternately switched, and the magnitude and direction of the currents 11 and 12 flowing through the primary and secondary sides of the transformer i 亦可 can also be changed with time. As can be seen from the embodiments of the present invention described above, the power converter has fewer transistors than many known power converters and is simpler in design' so that manufacturing costs and time can be reduced. In addition, the power converter can be controlled by only one switch to convert the DC voltage into an AC voltage, so that it can be controlled more easily and is more convenient for use in a Cold Cathode Fluorescent Lamp (CCFL). . Although the present invention has been disclosed in the above embodiments, it is not intended to limit the invention, and any one of ordinary skill in the art can make various changes and modifications without departing from the spirit and scope of the invention. The scope of the present invention is defined by the scope of the appended claims. The above and other objects, features, advantages and embodiments of the present invention will become more apparent. The detailed description of the formula is as follows: Fig. 1 is a schematic view showing a power converter for a cold cathode fluorescent lamp according to an embodiment of the present invention. 200814855 Figure 2 is a schematic diagram showing the operation of the power converter when the switch is turned on as shown in Figure 1. Figure 3 is a schematic diagram showing the operation of the power converter when the switch is closed as shown in Figure 1. Figure 4A is a schematic diagram showing the primary side voltage of the transformer. Fig. 4B is a schematic diagram showing the secondary side voltage of the transformer. [Main component symbol description] 100: Power converter 106: Drive circuit 102: DC voltage output circuit 108: Switch 104: Cold cathode fluorescent lamp 110: Transformer