1309104 九、發明說明 【發明所屬之技術領域】 本發明與風扇相關，特別涉及-種兼具溫控及脈寬糊速度控制的風 扇速度控制電路及速度控制方法。 【先前技術】 隨著電子產⑽快速發展，電子產品的發歸不斷料，散熱風扇被 廣泛應用於散熱裝置中。風扇轉速愈快，散熱效果愈佳，但相對噪音也愈 大。為了在献健絲的紐下降佩射音，乡賴扇速度控制方式 被提出。 如第三圖所示，為習知溫度控制轉速的特性曲線圖，橫軸代表風扇所 處的環境溫度’縱轴代表風扇轉速，該圖中假設風扇的最高轉速為5〇〇〇RpM (轉/分鐘）。當風扇所處得環境溫度在常溫或額定溫度時，如3〇至4〇攝氏 度時，風扇維持一定的低轉速，如1000RPM;當環境溫度逐漸上升，如從 40上升至50攝氏度時，風扇轉速亦呈比例地增加；當環境溫度達到非常高 的溫度，如50攝氏度時，風扇將維持最高轉速5〇〇〇11?]^。 如第四圖所示，為習知脈寬調節控制速度的特性曲線圖，橫軸代表脈 寬調制訊號的占空比（Duty Cycle)，縱軸代表風扇的轉速。根據晶片如中 央處理器的内部溫度，電腦主板將提供相應的占空比訊號，控制風扇在相 應的速度下工作。當晶片内部溫度較低時，在設定的占空比或以下，風扇 將在定速運行。第四圖中，在20%的占空比以下，該風扇皆以1〇〇〇RPM的 低速運行。而當晶片内部溫度升高時，主機板提供相應的占空比訊號，提 5 1309104 年月曰修(更)正替換頁 册什:纪i 〇 高風扇的轉速，當占空比為娜％時，風扇全速運行k s“ ▲可崎出，溫度控制方式是以風扇所處的位置，即晶片外部的 皿度變化來控觀摘轉速’因此其可以保證該環境溫度不會過高。 但是在-個系統中，熱量由發熱晶片散到環境中，尚需—定時間，因此— 個4的危險疋.晶片已經很熱，但由於還未來得及散到環境中使環境溫 度升命，風扇健會哺低的速度工作，因此晶片很可翻溫度過高而燒 毀反觀脈寬調制方式，其是以晶片内部溫度的變化來控制風扇的轉速， 因此其可以保證晶Μ部的溫度不會過高。但有時，晶片内部溫度確實已 經降低’㈣境溫度由於之辟義大量熱量^無法馬场溫，還需要風 扇以馬速坤’ ,_風祕受“ _溫度㈣，其概著降低轉速，導 致環境溫度無法快料下來，珊“顺的元件造成傷害。因此，現有 的速度控制方式财待改進，以兼顧晶片_溫度及環境溫度的需求。 【發明内容】 針對上述需求，發明人開發出一種可兼顧晶片内部溫度及晶片環境溫 度的風扇速度控制裝置及控制方法。 一種風扇速度控制電路包括脈寬調制訊號輸入電路、溫度檢測電路、 可編程控制器及風扇驅動電路。該脈寬調制訊號輸入電路用以提供一原始 脈寬調制訊號，該原始脈寬調制訊號與晶片内部溫度相對應。該溫度檢測 電路用以根據晶片周圍的環境溫度輸出對應的溫度訊號。該可編程控制器 用以接收上述原始脈寬調制訊號及溫度訊號，及根據上述原始脈寬調制訊 號及溫度訊號產生一新的脈寬調制訊號。該風扇驅動電路接收該新的脈寬 1309104 ί-------------------------------------------ι 丨表片qfh吏)正.替換頁; .調制訊號以控制風扇的速度^ 匕？ϋϋϋ__________________- j —韻扇速度控制方法，包括觀與U㈣溫度減相對應的原 始脈寬調制訊號及該晶片周圍的環境溫度訊號，然後根據該原始脈寬調制 訊號及％境溫度訊號產生-新的脈寬調制訊號，再將該新的脈寬調制訊號 輸入一風扇驅動電路，以控制該風扇工作於一對應的速度。 上述風扇速度控制電路及控制方法中，相較現有單一溫度控制或脈寬 調制控制的風扇速度控制方法’晶片内部的溫度及環境溫度同時作為風扇 ® 速度控制的考量因素，因此可以兼顧晶片内部及環境的散熱需求。 【實施方式】 以下以具體之實施例，對本發明揭示之各形態内容加以詳細說明。 請參照第一圖，為本發明一較佳實施例的控制電路框圖，主要包括有 PWM輸入電路100、PIC電路200 (Programmable 1C，可編程控制器）、 溫度檢測電路300、驅動電路400、速度回饋電路600，其中，該PWM輸 入電路100向PIC電路200輸入PWM訊號；溫度檢測電路3〇〇是為獲取 晶片環境溫度訊號並將該温度訊號輸入PIC電路200，本實施例中，該溫度 檢測電路可利用NTC熱敏元件將晶片環境溫度訊號轉換為電訊號輸入PIC 電路200 ;該PIC電路200綜合該PWM訊號及溫度訊號，選擇合適的風扇 速度，配合驅動電路400以驅動負載500 (驅動風扇轉動）。速度回饋電路 是藉由速度回饋方式精確調整風扇實際速度。 請參照第二圖，為上述PIC電路200的工作流程圖，本實施例是以型 號為PIC12F683的PIC為例。風扇啟動之後’ PIC首先進行初始化動作； 1309104 mJLz 3绦(更)正替換頁 接著，PIC讀取溫度檢測電路300輸入的溫度訊號’並將該溫度訊號存儲於 PIC的某一存儲空間’如記著dataO位置；然後PIC讀取PWM輸入電路1〇〇 輸入的PWM訊號’並將該溫度訊號存儲於PIC的另一存儲空間，如記著 datal位置·’然後根據存儲的PWM訊號及溫度訊號在一風扇速度列表中搜 尋對應的風扇速度，該風扇速度列表詳如後述；PIC根據該對應的風扇速度 向風扇驅動電路400輸出一調整之後的新PWM訊號，記著PWM(mix)訊 號’表示該PWM(mix)訊號是綜合原始PWM訊號與溫度訊號的結果，利用 該PWM(mix)訊號使風扇工作在該對應的速度。 接下來，為精確控制風扇實際速度，利用該速度回饋電路6〇〇向PIC 回饋的風扇速度對該風扇實際速度進行精確調整。此回饋方式為一般速度 控制所慣用之手段’本領域技術人員對此速度回饋方式原理及實現手段應 該了解，此不詳述。 以上介紹了 PIC電路200的工作流程，下面將重點介紹風扇速度列表。 該風扇速度列表是預先根據所要求達到的控制方式而設置。請先參閱 表1 ’是本發明第一實施例的風扇速度列表。相對於僅有PWM速度控制的 風扇速度列表，表1中的速度列表是綜合考慮PWM訊號及晶片環境溫度的 結果’其差異部分用灰色表示。其中，橫向向右代表晶片環境溫度的增加， 此溫度即為溫度控制電路3〇〇輸入PIC電路200的溫度訊號，縱向向下代 表原始PWM訊號的增加，此PWM訊號即為PWM輸入電路1〇〇輸入PIC 電路200的溫度訊號’因此根據橫向溫度訊號及縱向pwM訊號可以找到此 時風扇的轉速。表1中的速度是綜合PWM訊號及環境溫度訊號而設定的， 8 1309104 jf· 如前所述，當PIC根據PWM訊號及環境溫度訊號搜尋到一個對應的速度 時’PIC會根據該對應的速度向驅動電路400輸出與該速度對應的PWM(mix) ιίΐ说’控制風扇動作。 表1風扇速度列表一 ^溫度 占空 35 40 45 50 55 60 0% 1200 1 1390 : 、31580 、mo 1 1960 , 2150 10% 1580 1580 1580 r 1960 '' 2150v ;( 20% I960 1960 1960 I960 1960 ，2150 30% 2340 2340 2340 2340 2340 2340 40% 2720 2720 2720 2720 2720 2720 50% 3100 3100 3100 3100 3100 3100 60% 3480 3480 3480 3480 3480 3480 70% 3860 3860 3860 3860 3860 3860 80% 4240 4240 4240 4240 4240 4240 90% 4620 4620 4620 4620 4620 4620 100% 5000 5000 5000 5000 5000 50001309104 IX. Description of the Invention [Technical Field] The present invention relates to a fan, and more particularly to a fan speed control circuit and a speed control method that have both temperature control and pulse width paste speed control. [Prior Art] With the rapid development of electronic products (10), the return of electronic products continues to be expected, and cooling fans are widely used in heat sinks. The faster the fan speed, the better the heat dissipation, but the greater the relative noise. In order to reduce the sound of the shinning of the silk, the speed control method of the township fan was proposed. As shown in the third figure, the characteristic curve of the conventional temperature control speed, the horizontal axis represents the ambient temperature at which the fan is located, and the vertical axis represents the fan speed. In this figure, the maximum speed of the fan is assumed to be 5 〇〇〇 RpM. /minute). When the ambient temperature of the fan is at normal temperature or rated temperature, such as 3 〇 to 4 〇 Celsius, the fan maintains a certain low speed, such as 1000 RPM; when the ambient temperature rises gradually, such as from 40 to 50 ° C, the fan speed It also increases proportionally; when the ambient temperature reaches a very high temperature, such as 50 degrees Celsius, the fan will maintain a maximum speed of 5〇〇〇11?]^. As shown in the fourth figure, the characteristic curve of the conventional pulse width adjustment control speed, the horizontal axis represents the duty cycle of the pulse width modulation signal (Duty Cycle), and the vertical axis represents the rotation speed of the fan. Depending on the internal temperature of the chip, such as the central processor, the computer motherboard will provide a corresponding duty cycle signal to control the fan to operate at the appropriate speed. When the internal temperature of the wafer is low, the fan will run at a fixed speed at or below the set duty cycle. In the fourth figure, the fan operates at a low speed of 1 〇〇〇 RPM below 20% duty cycle. When the internal temperature of the chip rises, the motherboard provides the corresponding duty cycle signal, and the 5 1309104 曰 曰 repair (more) is replacing the page: ii 〇 high fan speed, when the duty cycle is N% When the fan runs at full speed, ks " ▲ can be taken out, the temperature control mode is based on the position of the fan, that is, the change of the degree of the outside of the wafer to control the picking speed" so it can ensure that the ambient temperature is not too high. In a system, heat is dissipated from the heat-generating wafer into the environment, and it takes a certain amount of time, so the danger of 4 is 疋. The wafer is already hot, but because it is still in the future, the ambient temperature rises and the fan is healthy. Will work at a low speed, so the wafer can be turned over too high and burned down to the pulse width modulation mode, which controls the fan speed by the change of the internal temperature of the wafer, so it can ensure that the temperature of the wafer is not too high. But sometimes, the internal temperature of the chip has indeed been reduced '(four) ambient temperature due to the large amount of heat ^ can not be the horse field temperature, also need the fan to Ma Su Kun ', _ wind secret by _ temperature (four), which is about to reduce the speed ,resulting in The temperature of the environment can not be expected, and the "shun components" cause damage. Therefore, the existing speed control method needs to be improved to meet the needs of the wafer temperature and the ambient temperature. [Inventive content] In response to the above demand, the inventors developed a A fan speed control device and a control method capable of balancing both the internal temperature of the wafer and the ambient temperature of the wafer. A fan speed control circuit includes a pulse width modulation signal input circuit, a temperature detecting circuit, a programmable controller, and a fan driving circuit. The pulse width modulation signal input The circuit is configured to provide a raw pulse width modulation signal corresponding to the internal temperature of the chip. The temperature detecting circuit is configured to output a corresponding temperature signal according to an ambient temperature around the wafer. The programmable controller is configured to receive the above The original pulse width modulation signal and the temperature signal, and generating a new pulse width modulation signal according to the original pulse width modulation signal and the temperature signal. The fan driving circuit receives the new pulse width 1309104 ί--------- ----------------------------------ι 丨表 qfh吏) 正. Replacement page; To control the speed of the fan ^ 匕 ϋϋϋ __________________- j - the fan speed control method, including observing the original pulse width modulation signal corresponding to the U (four) temperature minus and the ambient temperature signal around the wafer, and then modulating the signal according to the original pulse width and The % ambient temperature signal generates a new pulse width modulation signal, and then inputs the new pulse width modulation signal into a fan driving circuit to control the fan to operate at a corresponding speed. In the fan speed control circuit and the control method, the phase Compared with the conventional fan speed control method for single temperature control or pulse width modulation control, the temperature inside the wafer and the ambient temperature are considered as factors for the fan speed control. Therefore, the heat dissipation requirements inside the wafer and the environment can be balanced. The specific embodiments of the present invention will be described in detail with reference to specific embodiments. Referring to the first figure, a block diagram of a control circuit according to a preferred embodiment of the present invention includes a PWM input circuit 100, a PIC circuit 200 (Programmable 1C, a programmable controller), a temperature detecting circuit 300, and a driving circuit 400. The speed feedback circuit 600, wherein the PWM input circuit 100 inputs a PWM signal to the PIC circuit 200; the temperature detecting circuit 3 is configured to acquire a wafer ambient temperature signal and input the temperature signal into the PIC circuit 200. In this embodiment, the temperature The detecting circuit can convert the chip ambient temperature signal into the electrical signal input PIC circuit 200 by using the NTC thermal element; the PIC circuit 200 integrates the PWM signal and the temperature signal, selects a suitable fan speed, and cooperates with the driving circuit 400 to drive the load 500 (drive The fan turns). The speed feedback circuit accurately adjusts the actual fan speed by speed feedback. Please refer to the second figure for the working flow chart of the PIC circuit 200. This embodiment is based on the PIC of the PIC12F683. After the fan is started, the PIC first performs the initialization operation; 1309104 mJLz 3绦 (more) is replacing the page. Then, the PIC reads the temperature signal input by the temperature detecting circuit 300 and stores the temperature signal in a certain storage space of the PIC. The dataO position; then the PIC reads the PWM signal input from the PWM input circuit 1 ' and stores the temperature signal in another storage space of the PIC, such as the datal position · ' and then according to the stored PWM signal and temperature signal Searching for a corresponding fan speed in a fan speed list, the fan speed list is as described later; the PIC outputs an adjusted new PWM signal to the fan driving circuit 400 according to the corresponding fan speed, and the PWM (mix) signal indicates that the The PWM (mix) signal is the result of synthesizing the original PWM signal and the temperature signal, and the PWM (mix) signal is used to operate the fan at the corresponding speed. Next, in order to accurately control the actual fan speed, the actual speed of the fan is precisely adjusted by the fan speed fed back to the PIC by the speed feedback circuit 6〇〇. This feedback method is a method commonly used for general speed control. Those skilled in the art should understand the principle and implementation means of the speed feedback method, which is not detailed. The workflow of the PIC circuit 200 is described above, and the fan speed list will be highlighted below. The fan speed list is set in advance according to the required control mode. Please refer to Table 1 ' for the fan speed list of the first embodiment of the present invention. The speed list in Table 1 is a combination of the PWM signal and the ambient temperature of the wafer with respect to the fan speed list with only PWM speed control. The difference is indicated in gray. Wherein, the horizontal to the right represents an increase in the ambient temperature of the wafer, which is the temperature signal input to the PIC circuit 200 by the temperature control circuit 3, and the vertical downward direction represents the increase of the original PWM signal. The PWM signal is the PWM input circuit. 〇 Input the temperature signal of the PIC circuit 200. Therefore, the speed of the fan at this time can be found according to the lateral temperature signal and the vertical pwM signal. The speed in Table 1 is set by the integrated PWM signal and ambient temperature signal. 8 1309104 jf· As mentioned above, when the PIC searches for a corresponding speed based on the PWM signal and the ambient temperature signal, the PIC will be based on the corresponding speed. The PWM circuit (mix) corresponding to the speed is output to the drive circuit 400. Table 1 Fan speed list 1 ^ Temperature duty 35 40 45 50 55 60 0% 1200 1 1390 : , 31580 , mo 1 1960 , 2150 10% 1580 1580 1580 r 1960 '' 2150v ; ( 20% I960 1960 1960 I960 1960 , 2150 30% 2340 2340 2340 2340 2340 2340 40% 2720 2720 2720 2720 2720 2720 50% 3100 3100 3100 3100 3100 3100 60% 3480 3480 3480 3480 3480 3480 70% 3860 3860 3860 3860 3860 3860 80% 4240 4240 4240 4240 4240 4240 90 % 4620 4620 4620 4620 4620 4620 100% 5000 5000 5000 5000 5000 5000
從表1中可看出，在中高速狀態（設定以PWM占空比20%為分界點） 下’風扇速度仍然僅由PWM訊號控制，因此在同一 PWM占空比對應相同 的速度，如無論溫度多少，30%占空比皆對應2340rpm的轉速。而在低速 狀態下’同一 PWM占空比下的風扇速度是隨晶片環境溫度升高而升高的， 如在10%的占空比情況下，當環境溫度為45度時，風扇速度為I580rpm， 當環境溫度為50度時，風扇速度增加為1770rpm’而當環境溫度為55度時， 風扇速度增加為1960rpm。在本實施例中’風扇速度隨溫度升高而增加是呈 線性增加’例如’當環境溫度從45度上升至50度，風扇速度升高 1770-1580=190rpm ’當環境溫度從50度上升至55度，風扇速度升高 1960-1770=190rpm 〇 1309104 Γ~~~ --- • 年月日射更;正替換頁 II , 1-----!— . 由於本實施例所選用的PIC是16位元控制器，因此其最多可以設定255 .種PWM訊號變量及255種溫度變量。可以理解，PIC的位元數越高，風扇 速度變化越平滑，因此’本發明的風扇速度控制精度與pIC的選擇有關。 請再參閱表2，是本發明第二實施例的風扇速度列表。同樣，灰色部分As can be seen from Table 1, in the medium-high speed state (set to the PWM duty cycle of 20% as the cut-off point), the fan speed is still only controlled by the PWM signal, so the same PWM duty cycle corresponds to the same speed, such as The temperature is 30% duty cycle corresponding to 2340rpm. At low speeds, the fan speed at the same PWM duty cycle increases as the ambient temperature of the wafer increases. For example, at 10% duty cycle, when the ambient temperature is 45 degrees, the fan speed is I580rpm. When the ambient temperature is 50 degrees, the fan speed is increased to 1770 rpm' and when the ambient temperature is 55 degrees, the fan speed is increased to 1960 rpm. In the present embodiment, 'the fan speed increases linearly with increasing temperature', for example, when the ambient temperature rises from 45 degrees to 50 degrees, the fan speed increases by 1770-1580 = 190 rpm' when the ambient temperature rises from 50 degrees to 55 degrees, the fan speed increases 1960-1770=190rpm 〇1309104 Γ~~~ --- • Years and months are more daily; replace page II, 1-----!-. Since the PIC selected in this embodiment is 16-bit controller, so it can set up to 255 kinds of PWM signal variables and 255 temperature variables. It can be understood that the higher the number of bits of the PIC, the smoother the fan speed change, and therefore the fan speed control accuracy of the present invention is related to the selection of the pIC. Please refer to Table 2 again, which is a list of fan speeds according to the second embodiment of the present invention. Again, the gray part
表示岐綜合考慮PWM t峨及晶>;環賴度錢速制表與财慮pwM 訊號控制的速度列表的不同部分。表2相對於表i而言，其不僅低溫狀態 下的速度會隨著晶片環境溫度升高而升高，其高溫部分的速度亦會隨著晶 片環境溫度升高而升高，但僅當順訊號占空比達到腿時風扇速度才 達到全速運轉。 1309104 -紅41，2」一 表2風扇速度列表二It means that the PWM t峨 and crystals are comprehensively considered; the different parts of the speed list controlled by the pwM signal control. Table 2 relative to Table i, not only the speed in the low temperature state will increase with the increase of the ambient temperature of the wafer, but also the speed of the high temperature part will increase with the increase of the ambient temperature of the wafer, but only when When the signal duty cycle reaches the leg, the fan speed reaches full speed. 1309104 - Red 41, 2" one Table 2 fan speed list two
\^溫度 占空 35 40 45 50 55 60 0% 1200 1390 1580 1770 1960 2150 10% 1580 1580 1580 1770 1960 2150 20% 1960 I960 1960 1960 1960 十'名2150朵〆 30% 2340 2340 2340 2340 2340 f2506.3/ 40% 2720 2720 2720 2720 2720 ,；.2862；5 50% 3100 3100 3100 3100 3100 3218.8 60% 3480 3480 ' 3480 3480 3480 /3575 1 70% 3860 3860 3860 3860 3860 3931.3 80% 4240 4240 4240 4240 4240 90% 4620 4620 4620 4620 4620 '* 46418 * 100% 5000 5000 5000 5000 5000 5000 請再參閱表3 ’是本發明第三實施例中的風扇速度列表。同樣，灰色部 分表示的是综合考慮PW1V[訊號及晶片環境溫度之後速度列表與僅考慮 PWM訊號控制的速度列表的不同部分。表3中的速度無論在低溫狀態下、 - 高溫狀態下都有一定幅度的增加，而且風扇最高轉速是由PWM訊號及環境 溫度訊號綜合決定，比如當PWM訊號占空比為50%，環境溫度為60度時， • 按照習知技術，風扇速度僅由PWM控制，仍為3100rpm，但本發明考慮到 環境溫度已經很高，需要立即把環境溫度降下來，因此將風扇溫度設定為 全速運轉。 11 1309104 ki,lf(更)正替換頁 表3風扇速度列表三 溫度 占空 35 40 45 50 55 60 0% 1200 1580 1960 .„ . 2340 ^ 2720 3100 10% 1580 ；ί； 1960 .2340 , 2720,- 3100 ^ 3480 20% 1960 ^萍υ 2720；, 3100 . 3860 l , 30% 2340 ，丨:矻聊、 3100 令 3480 . 1 ,3860 々 4240 40% 2720 3100 ^:-,3480¾^ ' 3860 V· 1 ** * ? ,4240 4620 50% 3100 f}3480>：i： 3860 ' 4240 4620 • 5000 60% 3480 ·3860Γ；^ 4240 4620 •5000 5000 70% 3860 4240 4620 5000 5000 80% 4240 Μ620 5000 5000 5000 90% 4620 -5000 5000· 5000 5000 100% 5000 5000 5000 5000 5000 5000\^temperature duty 35 40 45 50 55 60 0% 1200 1390 1580 1770 1960 2150 10% 1580 1580 1580 1770 1960 2150 20% 1960 I960 1960 1960 1960 Ten 'name 2150 〆 30% 2340 2340 2340 2340 2340 f2506.3 / 40% 2720 2720 2720 2720 2720 ,;.2862;5 50% 3100 3100 3100 3100 3100 3218.8 60% 3480 3480 ' 3480 3480 3480 /3575 1 70% 3860 3860 3860 3860 3860 3931.3 80% 4240 4240 4240 4240 4240 90% 4620 4620 4620 4620 4620 '* 46418 * 100% 5000 5000 5000 5000 5000 5000 Please refer to Table 3 ' is a list of fan speeds in the third embodiment of the present invention. Similarly, the gray portion shows the different parts of the speed list after PW1V [signal and wafer ambient temperature and the speed list only considering PWM signal control. The speed in Table 3 has a certain increase in temperature at low temperature and high temperature, and the maximum fan speed is determined by the combination of PWM signal and ambient temperature signal, such as when the PWM signal duty cycle is 50%, ambient temperature. At 60 degrees, • According to the prior art, the fan speed is only controlled by PWM and is still 3100 rpm. However, the present invention considers that the ambient temperature is already high and needs to immediately lower the ambient temperature, so the fan temperature is set to run at full speed. 11 1309104 ki,lf (more) is replacing page table 3 fan speed list three temperature duty 35 40 45 50 55 60 0% 1200 1580 1960 .. . 2340 ^ 2720 3100 10% 1580 ; ί; 1960 .2340 , 2720, - 3100 ^ 3480 20% 1960 ^ υ 2720;, 3100 . 3860 l , 30% 2340 , 丨: 矻聊, 3100 令 3480 . 1 , 3860 々 4240 40% 2720 3100 ^:-,34803⁄4^ ' 3860 V· 1 ** * ? , 4240 4620 50% 3100 f}3480>:i: 3860 ' 4240 4620 • 5000 60% 3480 ·3860Γ;^ 4240 4620 •5000 5000 70% 3860 4240 4620 5000 5000 80% 4240 Μ620 5000 5000 5000 90% 4620 -5000 5000· 5000 5000 100% 5000 5000 5000 5000 5000 5000
表1至表3中的速度列表僅為本發明的舉例說明，也可以根據需要設 定其他的速度列表’但速度設定時應該保證速度的規律性變化，以避免速 度的急速變化帶來不悦的音質。 【圖式簡單說明】 第一圖為本發明實施例的電路框圖。 第二圖為本發明實施例的風扇速度控制流程圖。 第二圖為習知溫度控制風扇速度的特性曲線。 第四圖為習知脈寬調制控制風扇速度的特性曲線。 【主要元件符號說明】 100 PWM輸入電路 200 可編程控制器 300 溫度檢測電路 400 風扇驅動電路 500 負載 600 速度回饋電路 12The speed lists in Tables 1 to 3 are only examples of the present invention, and other speed lists may be set as needed. However, the speed setting should be guaranteed to ensure regular changes in speed to avoid unpleasant changes in speed. Sound quality. BRIEF DESCRIPTION OF THE DRAWINGS The first figure is a circuit block diagram of an embodiment of the present invention. The second figure is a flow chart of fan speed control according to an embodiment of the present invention. The second graph is a characteristic curve of a conventional temperature control fan speed. The fourth figure is a characteristic curve of the conventional pulse width modulation control fan speed. [Main component symbol description] 100 PWM input circuit 200 Programmable controller 300 Temperature detection circuit 400 Fan drive circuit 500 Load 600 Speed feedback circuit 12