201004472 八 、本案若有化學式時’請揭示最能顯不發明特徵的 化學式 九、發明說明： 【發明所屬之技術領域】 本發明係有關於發光二極體（led)的驅動，特別是 關於一種兩功率消耗效能的LED驅動系統及方法 【先前技術】 發光二極體（LED)普遍使用於各種電子裝置中並具 有各種用途。例如’ LED可以使用於液晶顯示器（lcd ) 的背光模組以提供背光源，或者使用於電荷轉合裝置 (CCD)照相機中以提供閃光照射。LED實際上為一種溫 度相關元件’換句話說’ LED的特性會隨著溫度的變化而 改變。第一圖顯示一 LED及其等效電路。一個LED相當 於一電壓源與一負 溫度係數 (negative-temperature-coefficient，NTC )電阻的串 聯。當通過LED的電流造成溫度上升時，此NTC電阻的 阻值會跟著下降’反之亦然。因此，當通過LED的電流為 固定時，則跨於LED陽極與陰極之間的電位（或稱為順 向電壓VF )會隨著溫度的上升而下降，反之亦然。 201004472 傳統 LED 驅動有兩種方法：定電壓 (constant-voltage, CV )驅動及定電流 (constant-current，CC)驅動。於傳統定電壓驅動方法 中，LED的陽極係接收一定電壓源。如前所述，即使陽極 接收定電壓，通過LED的電流仍然會改變。因此，LED 會因驅動電流的變化而改變其亮度。再者，傳統定電壓驅 動方法通常需串聯一限流（current-limiting)電阻，其 (’ 造成功率消耗的浪費。 於傳統定電流驅動方法中，控制通過LED的電流使其 為定值。雖然傳統定電流驅動的LED電流（及其亮度）不 會隨著順向電壓VF的變動而改變，但是，LED需與檢流 (current-sensing ) 電阻_聯，其也造成功率消耗的浪 費0 鑑於傳統定電壓或定電流驅動方法會造成功率消耗的 浪費，因此亟需提出一種新的驅動機制，其不但可以增高 功率消耗的效能，且可以維持驅動電流的穩定。 【發明内容】 鑑於上述，本發明的目的之一為提供一種LED的驅動 201004472 系統及方法，以穩定LED驅動電流及亮度，並增高功率消 耗的效能。 根據本發明實施例，驅動系統包含一定電流模式電 路，用以提供一固定電流給發光二極體；及一定電壓模式 電路，用以提供一固定電壓給發光二極體。使用一開關以 切換定電流模式電路與定電壓模式電路，使其分別進入定 C 電流模式及定電壓模式。藉此，發光二極體之順向電壓得 以維持於固定值，其功率消耗之效能因而得以增高。 【實施方式】 第二圖顯示本發明實施例之發光二極體（led)驅動 系統10。雖然本實施例以一個LED作為說明，然而所屬 ^ 技術領域中具有通常知識者當可以使用多個LED，且這些 LED彼此可以為串聯或併聯。在本實施例中，調節器 (regulator) 12連續地依次開啟（on)與關閉（off)(切 換）電晶體Q2，使得供應電壓Vin可以於電晶體Q2為開 啟時將能量儲存於電感L1，並於電晶體Q2為關閉時將所 儲存之能量傳送至LED D1的輸出電壓端點Vout。整流 (rectifying)二極體D2係用以阻止輸出電壓端點Vout 的電流不當流回供應電壓Vin處。調節器12的切換工作 201004472 週期（switching duty cycle)會根據誤差比較器（error comparator) 18的輸出作改變。例如，當誤差比較器18 的輸出增加時（其代表LED輪出電壓或電流降低），則調 節器12的切換工作週期會隨著增加，反之亦然。 根據本實施例，LED驅動系統10包含一檢流電阻 R3 ’其串聯於LED D1陰極與地之間。LED驅動系統1〇 ( 還包含一電壓分壓器（v〇itage divider) R1-R2，其連接 於LED D1的陽極（或電壓輸出端點v〇ut)與地之間。 誤差比較器18係用以比較一（反向輸入端）輸入電壓與 一（非反向輸入端）參考電壓。於不同模式下’該輸入電 壓與參考電壓會有所不同，此將於以下詳細描述。控制器 工3 (其細節將於以下詳述）係用以控制及調節LED驅動 系統10之操作。控制器13可以為硬體電路、軟體程式或 (其組合。再者，實務上，控制$ 13也可以區分為多個連 接或分離的功能方塊。 於操作％·，LED驅動系統10依次操作於兩種模式， 亦即定電流（CC)模式及定電壓（cv)模式。於圖式中， 此兩種模式之_切換係以開關sw來表示，其受控於控 制器13。當開關sw中的al_a2及M_b2為閉路（^咖） 201004472 時，即為定電流模式，其等效系統如第三A圖所示。相反 的，當開關SW中的a2-bl為閉路且al、b2為浮接 (floating)時，即為定電壓模式，其等效系統如第三B 圖所示。定電流（CC)模式及定電壓（CV)模式之工作 週期例示於第四圖的時序圖，其中定電流（CC)期間遠小 於定電壓（CV)期間。例如，定電流（CC)期間可以為 數毫秒（ms)，而定電壓（CV)期間則可持續數分鐘或者 C' 更久。 於定電流模式時，如第三A圖所示之系統方塊及第五 圖所示之流程，控制器13關閉（off)電晶體Q1 (步驟 51)。接著，於方塊14及步驟52，取得分壓端點d的分 壓VI，其係由跨於電壓輸出端點Vout與地之間的電壓分 壓器R1-R2所提供。在本實施例中，取得的分壓VI可以 藉由類比數位轉換器（ADC)轉換為數位形式，並暫存於 控制器13中作為後續操作之用。位於端點c的電壓（或 者為跨於檢流電阻R3的電位）藉由誤差比較器18之控 制，使其維持於預設之參考電壓Vref (方塊16)。根據基 本電路原理得知：201004472 VIII. If there is a chemical formula in this case, please disclose the chemical formula which can best show the characteristics of the invention. 9. Description of the invention: Technical field of the invention The present invention relates to the driving of a light-emitting diode (LED), in particular to a Two-power consumption efficiency LED driving system and method [Prior Art] Light-emitting diodes (LEDs) are commonly used in various electronic devices and have various uses. For example, the LED can be used in a backlight module of a liquid crystal display (LCD) to provide a backlight or in a charge transfer device (CCD) camera to provide flash illumination. The LED is actually a temperature dependent component. In other words, the characteristics of the LED change with temperature. The first figure shows an LED and its equivalent circuit. An LED is equivalent to a voltage source connected in series with a negative-temperature-coefficient (NTC) resistor. When the temperature through the LED causes the temperature to rise, the resistance of the NTC resistor will decrease, and vice versa. Therefore, when the current through the LED is fixed, the potential (or referred to as the forward voltage VF) across the anode and cathode of the LED decreases as the temperature rises, and vice versa. 201004472 There are two methods for traditional LED driving: constant-voltage (CV) driving and constant-current (CC) driving. In the conventional constant voltage driving method, the anode of the LED receives a certain voltage source. As mentioned earlier, even if the anode receives a constant voltage, the current through the LED will still change. Therefore, the LED changes its brightness due to changes in the drive current. Furthermore, the conventional constant voltage driving method usually requires a current-limiting resistor in series, which causes a waste of power consumption. In the conventional constant current driving method, the current passing through the LED is controlled to be constant. The traditional constant current driven LED current (and its brightness) does not change with the forward voltage VF, but the LED needs to be connected with the current-sensing resistor, which also causes a waste of power consumption. Conventional fixed voltage or constant current driving methods will cause waste of power consumption. Therefore, it is urgent to propose a new driving mechanism, which can not only improve the power consumption efficiency, but also maintain the stability of the driving current. [Invention] In view of the above, this One of the objects of the invention is to provide an LED driving system 201004472 system and method for stabilizing LED driving current and brightness and increasing power consumption efficiency. According to an embodiment of the invention, the driving system includes a current mode circuit for providing a fixed Current to the light emitting diode; and a voltage mode circuit for providing a fixed voltage to the light emitting diode A switch is used to switch between the constant current mode circuit and the constant voltage mode circuit to enter the constant C current mode and the constant voltage mode respectively, whereby the forward voltage of the light emitting diode is maintained at a fixed value, and the power consumption efficiency Therefore, the second figure shows a light-emitting diode (LED) driving system 10 according to an embodiment of the present invention. Although the present embodiment uses an LED as an illustration, it is generally known to those skilled in the art. A plurality of LEDs are used, and these LEDs may be connected to each other in series or in parallel. In the present embodiment, the regulator 12 sequentially turns on (on) and off (switches) the transistor Q2 sequentially, so that the supply voltage Vin is supplied. The energy can be stored in the inductor L1 when the transistor Q2 is on, and the stored energy is transmitted to the output voltage terminal Vout of the LED D1 when the transistor Q2 is off. The rectifying diode D2 is used to The current that prevents the output voltage terminal Vout is improperly returned to the supply voltage Vin. The switching operation of the regulator 12 201004472 cycle (switching duty cycle) is based on the error comparator The output of (error comparator) 18 is changed. For example, when the output of error comparator 18 is increased (which represents a decrease in LED wheeling voltage or current), the switching duty cycle of regulator 12 will increase, and vice versa. According to this embodiment, the LED driving system 10 includes a current-sense resistor R3' which is connected in series between the cathode of the LED D1 and the ground. The LED driving system 1〇 (also includes a voltage divider (R〇Rage divider) R1-R2, It is connected between the anode of LED D1 (or voltage output terminal v〇ut) and ground. Error comparator 18 is used to compare an (inverting input) input voltage to a (non-inverting input) reference voltage. The input voltage will differ from the reference voltage in different modes, which will be described in detail below. Controller 3 (which details will be detailed below) is used to control and regulate the operation of LED drive system 10. The controller 13 can be a hardware circuit, a software program or a combination thereof. Further, in practice, the control $13 can also be divided into a plurality of connected or separated functional blocks. In operation %, the LED driving system 10 operates in sequence. Two modes, namely constant current (CC) mode and constant voltage (cv) mode. In the figure, the switching of the two modes is represented by the switch sw, which is controlled by the controller 13. When the switch sw When al_a2 and M_b2 are closed circuit (^咖) 201004472, it is the constant current mode, and its equivalent system is shown in Figure A. Conversely, when a2-bl in switch SW is closed and al and b2 are When floating, it is the constant voltage mode, and its equivalent system is shown in the third B. The duty cycle of the constant current (CC) mode and the constant voltage (CV) mode is illustrated in the timing chart of the fourth figure. The constant current (CC) period is much less than the constant voltage (CV) period. For example, the constant current (CC) period may be several milliseconds (ms), while the constant voltage (CV) period may last for several minutes or C' longer. In constant current mode, the system block shown in Figure 3A and the process shown in Figure 5 The controller 13 turns off the transistor Q1 (step 51). Next, at blocks 14 and 52, a voltage division VI of the voltage dividing terminal d is obtained, which is between the voltage output terminal Vout and the ground. The voltage dividers R1-R2 are provided. In this embodiment, the obtained voltage division VI can be converted into a digital form by an analog-to-digital converter (ADC) and temporarily stored in the controller 13 for subsequent operations. The voltage at the terminal c (or the potential across the current-sense resistor R3) is maintained by the error comparator 18 to maintain the predetermined reference voltage Vref (block 16). According to the basic circuit principle:
Vl=(R2/(Rl+R2))*Vout 201004472Vl=(R2/(Rl+R2))*Vout 201004472
Vout= (V1 / R2) * (R1 + R2) 藉此，控制器13可推導得到LEDD1的順向電壓 如下（步驟53): VF=Vout-Vref= (V1 / R2) * (R1+R2) -Vref 接下來，LED驅動系統1 〇進入定電壓（cv )模式r 、工、、模 f 式之切換可以由控制器13來執行），如第三b圖所示之系 統方塊及第五圖所示之流程。控制器13開啟（〇11)電曰 體Q1(步驟54 )(作為旁路電晶體之用），因而將led 〇 1 的陰極連接至地，並旁路（bypass)或繞過電阻r3。換 句話說，沒有電流會通過電阻R3，因而於定電壓（Cv) 模式中，電阻R3也就沒有功率消耗了。接著，於步驟55， 輸入至誤差比較器18的參考電壓16被改變為一個新參考 L；電壓值Vl-Vref*R2/(Rl+R2)。在本實施例中，控制器Q 藉由數位類比轉換器（DAC)提供類比形式之新參考電髮 值給誤差比較器18。位於端點d的電壓即會趨向此新表专 電壓值VbVref*R2/(Rl+R2)。根據基本電路原理可得到 以下關係： V1 -VrePR2 / (R1+R2)=(R2 / (R1+R2)) *V〇ut 或 201004472Vout = (V1 / R2) * (R1 + R2) Thereby, the controller 13 can derive the forward voltage of the LED D1 as follows (step 53): VF = Vout - Vref = (V1 / R2) * (R1 + R2) -Vref Next, the LED drive system 1 〇 enters the constant voltage (cv) mode r, the work, the mode f mode can be executed by the controller 13), as shown in the third b system block and the fifth figure The process shown. The controller 13 turns on (〇11) the electrical body Q1 (step 54) (for use as a bypass transistor), thereby connecting the cathode of the led 〇 1 to ground and bypassing or bypassing the resistor r3. In other words, no current will pass through the resistor R3, so in the constant voltage (Cv) mode, the resistor R3 has no power consumption. Next, at step 55, the reference voltage 16 input to the error comparator 18 is changed to a new reference L; the voltage value Vl - Vref * R2 / (Rl + R2). In the present embodiment, controller Q provides a new reference electrical value in analogy to error comparator 18 by a digital analog converter (DAC). The voltage at the terminal d tends to the new table voltage value VbVref*R2/(Rl+R2). According to the basic circuit principle, the following relationship can be obtained: V1 -VrePR2 / (R1+R2)=(R2 / (R1+R2)) *V〇ut or 201004472
Vout=(Vl-Vref*R2/(Rl+R2))*((Rl+R2)/R2)=Vout=(Vl-Vref*R2/(Rl+R2))*((Rl+R2)/R2)=
(Vl/R2)*(Rl+R2)-Vref=VF 藉此，LED D1的順向電壓VF即可維持於固定電壓 值VF。值得注意的是，電阻R3於定電壓模式中不再是作 為限流電阻，因此於此模式下電阻R3不會有功率消耗。 藉由增加定電壓（CV)模式的工作週期（第四圖）使其盡 可能大，則功率消耗的效能即可較傳統定電流驅動方法或 定電壓驅動方法來得高。 以上所述僅為本發明之較佳實施例而已，並非用以限 定本發明之申請專利範圍；凡其它未脫離發明所揭示之精 神下所完成之等效改變或修飾，均應包含在下述之申請專 利範圍内。 【圖式簡單說明】 第一圖顯示一 LED及其等效電路。 第二圖顯示本發明實施例之發光二極體驅動系統。 第三A圖顯示第二圖之LED驅動系統處於定電流模式時 的等效系統。 弟二B圖顯不弟-一圖之LED驅動糸統處於定電壓模式時 11 201004472 的等效系統。 第四圖顯示定電流模式（第三A圖）與定電壓模式（第三 B圖）的工作週期。 第五圖顯示第二至三B所示驅動系統的流程圖。 【主要元件符號說明】 10 發光二極體驅動系統 12 調節器 f k 13 控制器 14 分壓VI之取得 16 參考電壓 18 誤差比較器 51-55 驅動流程步驟 CC 定電流驅動 f CV 定電壓驅動(Vl/R2)*(Rl+R2)-Vref=VF Thereby, the forward voltage VF of the LED D1 can be maintained at a fixed voltage value VF. It is worth noting that resistor R3 is no longer used as a current limiting resistor in constant voltage mode, so resistor R3 will not have power consumption in this mode. By increasing the duty cycle of the constant voltage (CV) mode (figure 4) to make it as large as possible, the power consumption can be made higher than the conventional constant current driving method or the constant voltage driving method. The above description is only the preferred embodiment of the present invention, and is not intended to limit the scope of the present invention; all other equivalent changes or modifications which are not departing from the spirit of the invention should be included in the following Within the scope of the patent application. [Simple description of the diagram] The first figure shows an LED and its equivalent circuit. The second figure shows a light emitting diode driving system according to an embodiment of the present invention. Figure 3A shows the equivalent system for the LED drive system of Figure 2 in constant current mode. Brother II B shows the same system - the equivalent of the LED driver system in the constant voltage mode 11 201004472 equivalent system. The fourth graph shows the duty cycle of the constant current mode (third A picture) and the constant voltage mode (third B picture). The fifth figure shows a flow chart of the drive system shown in the second to third B. [Main component symbol description] 10 LED driver system 12 Regulator f k 13 Controller 14 Voltage divider VI acquisition 16 Reference voltage 18 Error comparator 51-55 Drive flow step CC constant current drive f CV constant voltage drive
V NTC 負溫度係數電阻 VF 順向電壓 D1 發光二極體 Q1 電晶體 Q2 電晶體V NTC Negative Temperature Coefficient Resistor VF Forward Voltage D1 Luminous Diode Q1 Transistor Q2 Transistor
Vin 供應電壓Vin supply voltage
Vout 輸出電壓 12 201004472 L1 電感 D2 整流二極體 R3 檢流電阻 R1-R2 電壓分壓器 C 端點 d 分壓端點 VI 分壓 r sw 開關Vout Output Voltage 12 201004472 L1 Inductor D2 Rectifier Diode R3 Current Sense Resistor R1-R2 Voltage Divider C End Point d Dividing End Point VI Dividing r sw Switch