201146081 六、發明說明： 【發明所屬之技術領域】 本發明係有關一種調光(dimming)電路及方法，特別是關 ' 於一種發光二極體(LED)的調光電路及方法。 【先前技術】 如圖1所示，習知的LED調光電路包括升壓積體電路 (IC)10將電池電壓vbat轉換為驅動電壓ν〇給LED及功能忙 12 ’功能1C 12提供調光信號Dpwm切換與LED串聯的開關 Μ以調節通過LED之電流lied的平均值，達到明亮㈣ght)、 微暗(dim)及閃爍(flashing)等調光控制。升壓ic 及功能ic 12 的電路及操作都是很成熟的技術，不再贅述。當功能1C η切 斷開關Μ而中斷電流iied時，由於沒有接地路徑供釋放電容 Cout的電荷，因此驅動電壓v〇將持續上升，一旦驅動電壓％ 大於臨界值，升壓Ic 10便進入過電壓保護模式。其後，在功 能1C 12打開(tum on)開關M時，儲存在電容c〇ut的電荷將湧 入LED，因此LED承受很大的電壓直到驅動電壓v〇降回原 來的準位，這可能導致LED的壽命縮短。軸此電路讓功能 1C 12在LED關閉時仍能繼續工作，但升壓汇1〇及功能汇12 都要承受«的電M，又魏IC 12易受其電源的影響，故此 電路在調光週期期間可能出錯。 圖2係另-習知的LED調光電路，其中功能ΐ(： 12的電 原係由獨立的電池伽2供應，且提供的調光鶴邱魏係 致能(enab攸禁能咖疏)升壓Ic 1〇以達到調光控制。在 [S]201146081 VI. Description of the Invention: [Technical Field] The present invention relates to a dimming circuit and method, and more particularly to a dimming circuit and method for a light emitting diode (LED). [Prior Art] As shown in FIG. 1, a conventional LED dimming circuit includes a boost integrated circuit (IC) 10 that converts a battery voltage vbat into a driving voltage ν 〇 to provide dimming to an LED and a function busy 12 'function 1C 12 The signal Dpwm switches the switch 串联 in series with the LED to adjust the average value of the current through the LED to achieve dimming control such as bright (four) ght), dim and flashing. The circuit and operation of the boost ic and the function ic 12 are very mature technologies and will not be described again. When the function 1C η cuts off the switch and interrupts the current iied, since there is no ground path for discharging the charge of the capacitor Cout, the driving voltage v〇 will continue to rise. Once the driving voltage % is greater than the critical value, the boost Ic 10 enters the overvoltage. Protection mode. Thereafter, when the function 1C 12 turns on the switch M, the charge stored in the capacitor c〇ut will flood into the LED, so the LED is subjected to a large voltage until the driving voltage v〇 falls back to the original level, which may Lead to shortened LED life. This circuit allows the function 1C 12 to continue to work when the LED is turned off, but the booster port 1 and the function sink 12 are subject to the «electric M, and the Wei IC 12 is susceptible to its power supply, so the circuit is dimming. There may be an error during the cycle. Figure 2 is another conventional LED dimming circuit, in which the function ΐ (: 12 of the electrogen source is supplied by an independent battery gamma 2, and the provided dimming crane Qiu Wei system enables (enab banned coffee) Boost Ic 1〇 to achieve dimming control. At [S]
LED為π的期間’功能ic 12致能升麗IC 10使其提供等於LED 正常順向偏壓的驅動電壓ν〇。在LED為暗的期間，功能IC 12 π月b升壓1C 10，因此驅動電壓v〇不會上升導致升壓I?進 入過電壓保護模式，整個系統比較安全，也不會造成LED的 壽命縮短。然而，對大部分的功能IC 12而言，當電池電壓 Vbat2低於0.9V時將無法工作，但電池電壓施12低於〇 9V 時’升壓IC 10也許仍能正常操作，故此電路無法有效利用電 池的此量。此外，假設在led被點亮時，驅動電墨v〇為led 的正常順向偏壓，例如3.6V，在LED變暗時，驅動電壓 Vo=Vbatl-VD，因此，當LED由亮變暗或由暗變亮時，其上 的電壓將劇烈變化，若Vbatl=1 5V，而vd=〇 7V，則LED上 的電壓變化量約2.8V。隨著電池電壓Vbatl的下降，此電壓 變化量會縣上升，綱的電觀化會使LED的壽命縮短。 因此’一種延長LED壽命的調光電路及方法，乃為所冀。 【發明内容】 本發明的目的之一，在於提出一種LED調光電路及方法。 本發明的目的之一，在於提出一種避免LED遭受劇烈的 電壓變化的調光電路及方法。 一種根據本發明的LED調光電路及方法，係根據功能Ic 提供的調光信號選擇第一電壓設定信號或第二電壓設定信 號，進而決定供應給LED的輸出電壓為第一驅動電壓或第二 驅動電壓。該輸出電壓亦供應給該功能1C，且不論是該第一 驅動電壓或第二驅動電壓，其大小皆足以驅動該功能IC。 201146081 因為控制該第一及第二驅動電壓的大小，所以避免led 在由亮變暗或由暗變亮時遭受劇烈的電壓變化，因而延長該 LED的壽命。 【實施方式】 本發明的調光方法係朝向控制致能及禁能LED的驅動電 壓，以避免LED在變亮及變暗時遭受劇烈的電壓變化，例如 從接地電壓至順向偏壓。「禁能」一詞係指在人眼中LED不 亮。以順向偏壓為3.6V、功率為3W的LED為例，當電壓為 2.5V時，該LED的電流Hed完全截止，故可設定2.5V為使 該LED變暗的驅動電壓，而3 6v為使該LED變亮的驅動電 壓。此外，供給LED的驅動電壓亦可供給功能IC及其他電路。 由於在LED變暗時，該驅動電壓仍有2 5V，因此功能汇及 其他電路在LED變暗時仍可正常工作。 如圖3所示’根據本發明的LED調光電路包括功能汇12 提供調光錢Dpwm，霞奴電路22提㈣設定信號 EA1及EA2 ’選擇器2〇根據調光信號邱评瓜從電壓設定信號 EA1及EA2選取其中之一給電源供應器％，電源供應器μ 根據選擇S 2G的輪出蚊其輸出電壓為驅動輕V。〗或似 供給LED及功成ic 12。不論是驅動電壓或灿其大小 皆足以驅動功能ic 12。t調光錢Dpwm為高準位時，選 器20送出電壓設定信號EA1，因此電源供應器％的輸出電壓 為致能LED _動職偏。#調絲號Dpwm為低準 選擇器2〇送出電塵設定信號EA2，因此電源供應器24的輸出 [S] 5 電壓為禁能LED的驅動電壓Vo2。驅動電聲v〇2可藉提供給 電壓設定電路22的設定信號Sset來設定，設定信號Sset可由 外部或内部提供。電源供應器24可以是任何可供應電源的電 路，例如降壓式電源供應器、升壓式電源供應器或線性電源供 應器，而且電源供應器24也不一定是連接在LED的陽極，也 可以連接在LED的陰極。 圖4係圖3中的選擇器20、電壓設定電路22及電源供應 器24的實施例。在此實施例中，電源供應器24為非同步升壓 式電源供應器’其包括脈寬調變(PWM)比較器28比較鑛齒波 Sramp及來自選擇器2〇的信號產生脈寬調變信號Spwm，正 反器26根據脈寬調變信號Spwm及時脈CLK切換電晶體μ 而產生驅動電壓Vol或Vo2。電壓設定電路22包括誤差放大 器30放大驅動電壓v〇l或Vo2與參考電壓Vref2之間的差值 產生電壓設定信號EA2，其中參考電壓Vref2可以因應設定信 號Sset而調整’感測電阻Rfb與LED串聯以感測通過LED的 電流lied而產生回授信號Vfb，誤差放大器32放大回授信號 Vfb及參考電壓Vrefl之間的差值產生電壓設定信號^卜選 擇器20包括開關SW1 ’當調光信號Dpwm為高準位時，開關 SW將電壓設定信號EA1傳送至PWM比較器28，使電源供 應器24的輸出電壓為驅動電壓Vol，進而讓電流lied穩定在 Vrefl/Rfb ;當調光信號Dpwm為低準位時，開關SW1將電壓 設定信號EA2傳送至PWM比較器28，使電源供應器24的輸 出電壓穩定在預設的低電壓Vo2=Vref2。 圖5係根據本發明的第二實施例，此LED調光電路與圖 201146081 3的電路同樣包括功能IC 12、選擇器20及電源供應器24，此 外還包括電流箝制電路40及自動電壓偵測器42。此LH)調 光電路在啟動時，電流箝制電路40先使其進入短暫的第一階 段，在第一階段期間，電流箝制電路4〇控制電源供應器24提 供小電流給LED，例如低於1〇〇μΑ的小電流，同時令自動電 壓偵測器42偵測及儲存此時LED的電壓以得到電壓設定信號 Vp。在第一階段結束後，電流箝制電路4〇使LED調光電路 進入正常操作的第二階段，在第二階段期間，自動電壓憤測器 • 42不再侧LED的電壓，而電源供應器24也停止供應該預 設的小電流’由選擇器20根據調光信號Dpwm從電壓設定信 號Vref及Vp之間選擇一個給電源供應器％，使電源供應器 24的輸出電縣驅動電壓v〇1或v〇2，供給㈣及功能忙 12。不論是驅動電壓Vol或v〇2，其大小皆足以驅動功能ic 12。 。圖6係圖5中的選擇器20、電源供應器24及自動電壓偵 測器42的實施例。在此實施例中，電源供應$ %為線性電源 供應器’其包括誤差放大H 44、電晶體Μ、電流源Is、開關 _ SW3及開關SW4。誤差放大器44根據其兩輸入之間的差值控 制電a日體]VI以調節通過電晶體M的電流1〇。開關SW3連接 在電阳體Μ及LED之間，受控於來自電流箝制電路4〇的信 號W ’開關SW4連接在電流源jaLED之間，受控於來自 電抓箝制電路40的信號w。自動電壓偵測器42包括由電容 \ CS及開闕SW2 ·组成的取樣及維持電路，開關SW2受控於信 號W。選擇器20包括開關SW1根據調光信號砰麵將電壓 «λ疋4號Vp或Vref傳送給誤差放大器体在第—階段期間， 201146081 is號妒1打開(turn on)開關SW2及SW4，信號妒2關閉(turn ofi) 開關SW3，由電流源Is供應約1〇μΑ的電流給LED，LED因 而產生電壓Vp儲存到電容Cs。在第二階段期間，信號0關 閉開關SW2及SW4，信號屮2打開開關SW3，因此停止電流 源Is供應電流給LED，自動電壓偵測器42也停止對LED的 電壓取樣，開關SW1根據調光信號Dpwm將電壓設定信號Vref 或Vp傳送給誤差放大器44，誤差放大器44根據LED的電壓 及電壓設定信號Vref或Vp之間的差值調節電流1〇，因此電源 # 供應器24的輸出電壓為驅動電壓Vol或Vo2，供給LED。 【圖式簡單說明】 圖1係習知的LED調光電路； 圖2係另一習知的LED調光電路； 圖3係本發明的第一實施例； 圖4係圖3中的選擇器、電壓設定電路及電源供應器的實 施例； 籲 圖5係本發明的第二實施例；以及 圖6係圖5中的選擇器、電源供應器及自動電壓偵測器的 實施例。 【主要元件符號說明】 10升壓積體電路 12功能積體電路 20選擇器 [S1 201146081 電壓設定電路 電源供應器 正反器 PWM比較器 誤差放大器 誤差放大器 電流箝制電路 自動電壓偵測器 誤差放大器The period during which the LED is π' functional ic 12 enables the IC 10 to provide a driving voltage ν 等于 equal to the normal forward bias of the LED. During the period when the LED is dark, the function IC 12 π month b boosts 1C 10, so the driving voltage v 〇 does not rise and causes the boost I to enter the over voltage protection mode. The whole system is safe and does not cause the LED life to be shortened. . However, for most of the functional ICs 12, when the battery voltage Vbat2 is lower than 0.9V, it will not work, but when the battery voltage is lower than 〇9V, the boost IC 10 may still operate normally, so the circuit cannot be effective. Take advantage of this amount of battery. In addition, it is assumed that when the LED is lit, the driving ink v is a normal forward bias of the LED, for example 3.6V, and when the LED is dimmed, the driving voltage Vo=Vbatl-VD, therefore, when the LED is dimmed from bright to dark Or when it is darkened, the voltage on it will change drastically. If Vbatl=1 5V, and vd=〇7V, the voltage change on the LED is about 2.8V. As the battery voltage Vbatl drops, this voltage change will rise in the county, and the electrical appearance of the class will shorten the life of the LED. Therefore, a dimming circuit and method for prolonging the life of an LED are used. SUMMARY OF THE INVENTION One object of the present invention is to provide an LED dimming circuit and method. One of the objects of the present invention is to provide a dimming circuit and method that avoids the LED being subjected to severe voltage changes. An LED dimming circuit and method according to the present invention, according to the dimming signal provided by the function Ic, selecting a first voltage setting signal or a second voltage setting signal, thereby determining whether the output voltage supplied to the LED is the first driving voltage or the second Drive voltage. The output voltage is also supplied to the function 1C, and the magnitude of the first driving voltage or the second driving voltage is sufficient to drive the functional IC. Since the size of the first and second driving voltages is controlled, the LED is prevented from being subjected to a drastic voltage change when it is dimmed from light or dark, thereby prolonging the life of the LED. [Embodiment] The dimming method of the present invention is directed toward controlling the driving voltage of the enabling and disabling LEDs to prevent the LED from being subjected to severe voltage changes when it is brightened and darkened, for example, from ground voltage to forward bias. The term "disabled" means that the LED is not bright in the human eye. Taking an LED with a forward bias of 3.6V and a power of 3W as an example, when the voltage is 2.5V, the current Hed of the LED is completely cut off, so 2.5V can be set as the driving voltage for dimming the LED, and 3 6v The driving voltage for making the LED brighter. In addition, the driving voltage supplied to the LED can also be supplied to the functional IC and other circuits. Since the driving voltage is still 2 5V when the LED is dimmed, the function sinks and other circuits can still work normally when the LED is dimmed. As shown in FIG. 3, the LED dimming circuit according to the present invention includes a function sink 12 to provide dimming money Dpwm, Xia Nu circuit 22 (4) setting signals EA1 and EA2 'selector 2 〇 according to the dimming signal The signals EA1 and EA2 select one of them to the power supply %, and the power supply μ drives the light V according to the output voltage of the selected mosquito of the S 2G. 〗 〖Or like to supply LED and work ic 12. Both the drive voltage and the size of the drive are sufficient to drive the function ic 12. When the dimming money Dpwm is at a high level, the selector 20 sends out the voltage setting signal EA1, so the output voltage of the power supply % is the enabling LED _ active bias. #调丝号Dpwm is the low level selector 2〇 sends the dust setting signal EA2, so the output [S] 5 voltage of the power supply 24 is the driving voltage Vo2 of the disabled LED. The drive electroacoustic v〇2 can be set by a setting signal Sset supplied to the voltage setting circuit 22, which can be supplied externally or internally. The power supply 24 can be any circuit that can supply power, such as a buck power supply, a boost power supply, or a linear power supply, and the power supply 24 is not necessarily connected to the anode of the LED. Connected to the cathode of the LED. 4 is an embodiment of the selector 20, the voltage setting circuit 22, and the power supply 24 of FIG. In this embodiment, the power supply 24 is a non-synchronous boost power supply that includes a pulse width modulation (PWM) comparator 28 to compare the mineral tooth wave Sramp and the signal from the selector 2 to generate pulse width modulation. The signal Spwm, the flip-flop 26 switches the transistor μ according to the pulse width modulation signal Spwm and the pulse CLK to generate the driving voltage Vol or Vo2. The voltage setting circuit 22 includes an error amplifier 30 that amplifies the difference between the driving voltage v〇1 or Vo2 and the reference voltage Vref2 to generate a voltage setting signal EA2, wherein the reference voltage Vref2 can be adjusted according to the setting signal Sset. The sensing resistor Rfb is connected in series with the LED. The feedback signal Vfb is generated by sensing the current led through the LED, and the error amplifier 32 amplifies the difference between the feedback signal Vfb and the reference voltage Vref1 to generate a voltage setting signal. The selector 20 includes the switch SW1 'When the dimming signal Dpwm When the level is high, the switch SW transmits the voltage setting signal EA1 to the PWM comparator 28, so that the output voltage of the power supply 24 is the driving voltage Vol, and the current lied is stabilized at Vrefl/Rfb; when the dimming signal Dpwm is low At the level, the switch SW1 transmits the voltage setting signal EA2 to the PWM comparator 28, so that the output voltage of the power supply 24 is stabilized at the preset low voltage Vo2 = Vref2. 5 is a second embodiment of the present invention, the LED dimming circuit and the circuit of FIG. 201146081 3 also include a function IC 12, a selector 20 and a power supply 24, and further includes a current clamping circuit 40 and automatic voltage detection. 42. When the LH) dimming circuit is activated, the current clamping circuit 40 first enters a brief first phase. During the first phase, the current clamping circuit 4〇 controls the power supply 24 to provide a small current to the LED, for example, less than 1 The small current of 〇〇μΑ causes the automatic voltage detector 42 to detect and store the voltage of the LED at this time to obtain the voltage setting signal Vp. After the end of the first phase, the current clamping circuit 4 causes the LED dimming circuit to enter the second phase of normal operation. During the second phase, the automatic voltage inversion sensor 42 no longer side LED voltage, while the power supply 24 The supply of the preset small current is also stopped. 'The selector 20 receives a power supply % from the voltage setting signals Vref and Vp according to the dimming signal Dpwm, so that the output of the power supply 24 is driven by the voltage v〇1. Or v〇2, supply (four) and function busy 12. Whether it is the drive voltage Vol or v〇2, it is large enough to drive the function ic 12. . 6 is an embodiment of selector 20, power supply 24, and automatic voltage detector 42 of FIG. In this embodiment, the power supply $% is a linear power supply unit' which includes error amplification H 44, transistor Μ, current source Is, switch _ SW3, and switch SW4. The error amplifier 44 controls the electrical a-body VI according to the difference between its two inputs to regulate the current through the transistor M. The switch SW3 is connected between the electric male body and the LED, and is controlled by a signal W from the current clamping circuit 4'. The switch SW4 is connected between the current source jaLED and is controlled by the signal w from the electric gripping circuit 40. The automatic voltage detector 42 includes a sampling and sustaining circuit composed of a capacitor \ CS and an opening SW2, and the switch SW2 is controlled by a signal W. The selector 20 includes a switch SW1 for transmitting a voltage «λ疋4 Vp or Vref to the error amplifier body according to the dimming signal. During the first phase, the 201146081 is 妒1 turns on the switches SW2 and SW4, the signal 妒2 Turn off the switch SW3, the current source Is supplies about 1 〇μΑ of current to the LED, and the LED thus generates a voltage Vp to be stored in the capacitor Cs. During the second phase, signal 0 turns off switches SW2 and SW4, and signal 屮2 turns on switch SW3, thus stopping current source Is to supply current to the LED, automatic voltage detector 42 also stops sampling the voltage of LED, switch SW1 is based on dimming The signal Dpwm transmits the voltage setting signal Vref or Vp to the error amplifier 44, and the error amplifier 44 adjusts the current 1〇 according to the difference between the voltage of the LED and the voltage setting signal Vref or Vp, so that the output voltage of the power supply #24 is driven. The voltage Vol or Vo2 is supplied to the LED. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a conventional LED dimming circuit; Fig. 2 is another conventional LED dimming circuit; Fig. 3 is a first embodiment of the present invention; Fig. 4 is a selector of Fig. 3. Embodiments of the voltage setting circuit and the power supply; FIG. 5 is a second embodiment of the present invention; and FIG. 6 is an embodiment of the selector, the power supply, and the automatic voltage detector of FIG. [Main component symbol description] 10 boost integrated circuit 12 function integrated circuit 20 selector [S1 201146081 Voltage setting circuit Power supply forward and reverse converter PWM comparator error amplifier error amplifier current clamp circuit automatic voltage detector error amplifier