关于Fuse相关的培训资料

1、Littelfuse OC Selection TrainingAnthony Chang2Confidential and Proprietary to Littelfuse, Inc. 2006 Littelfuse, Inc. All rights reserved.Who We Are. Littelfuse Inc.成立於成立於1927年，為專業製造保險絲公司。自年，為專業製造保險絲公司。自1999至至2005年投入了過電壓保護元件製造而成為一家線路年投入了過電壓保護元件製造而成為一家線路保護元件的保護元件的Circuit Protection Provider的跨國公司。的跨國公司

2、。 總總部設在美國伊利諾州部設在美國伊利諾州Des Plaines市，擁有十幾家工廠分市，擁有十幾家工廠分佈在美、歐、亞三大洲七個國家，在世界各地設有區域性佈在美、歐、亞三大洲七個國家，在世界各地設有區域性營銷中心。營銷中心。3Confidential and Proprietary to Littelfuse, Inc. 2006 Littelfuse, Inc. All rights reserved.1927 First instrument fuses1976 ATO blade fuse1992 Surface mount (D-Case)1994 Square Nano fuse1

3、994 A-Case (1206)1996 0603 surface mount1997 PTC Resettable Device 1999 ESD Protectors/Harris Suppression2002Lead Free 1206, 0603 & 0402 size Fuse2002Semitron Over Voltage Products (TVS Diodes & GDT)2003TECCOR (Power Thyristor & Sidactor)2004 Wickmann Integration 4Confidential and Propri

4、etary to Littelfuse, Inc. 2006 Littelfuse, Inc. All rights reserved.Fuse selectionFuse reviewBasics of fuseApplication of AspectsSelecting a fuse Fuse rating I2t ratingExample of in-rush currentDemonstration of trip timesDownsides and solutionsOverview:5Confidential and Proprietary to Littelfuse, In

5、c. 2006 Littelfuse, Inc. All rights reserved.Fuse functionality - Limited current vs Potential currentCircuit response without fuse protection current is eventually disrupted (in an unpredictable manner) due to the failure of a component or circuit board traceFused circuit - current is interrupted i

6、n a controlled manner (by the fuse) to avoid damage to circuit components - circuit is allowed to fail “gracefully”I (A)t FuseA Fuse is a Temperature Sensitive Device that serves as an intentional Weak Link in an electrical circuit. It interrupts overload and short-circuit conditions when its metall

7、ic element melts; thereby halting the overcurrent condition.6Confidential and Proprietary to Littelfuse, Inc. 2006 Littelfuse, Inc. All rights reserved.Fuse Review: Construction Traditional Cartridge Type Vs. Slimline Thin Film TypeCartridge fuseThin Film fuseThe metallic element (filament) melts an

8、d disconnects the power to the circuit.7Confidential and Proprietary to Littelfuse, Inc. 2006 Littelfuse, Inc. All rights reserved. SMD Fuse 1.- Ceramic Body. 2.- Fuse end caps Tin-Lead and RoHS (Silver or Gold) plated caps. 3.- Filament (Ag Alloy) for 451 & Ceramic Yarn and Tin plate wire for 4

9、52 451 series 452 series8Confidential and Proprietary to Littelfuse, Inc. 2006 Littelfuse, Inc. All rights reserved.FuseSolutions for: AC mains overcurrent protection Tip/Ring circuit protectionCartridge and leaded fuse Industry standard form factors (cartridge, axial leaded, radial leaded) Designed

10、 to IEC, UL, METI Fast-acting, medium-acting, and slo-blo versions available Low, enhanced and high-breaking capacity versions available Key feature is the wide array of form factors, amperage ratings, voltage ratings and breaking capacities that are available 9Confidential and Proprietary to Littel

11、fuse, Inc. 2006 Littelfuse, Inc. All rights reserved.Cartridge, leaded fusePower supplyPower adaptorTVSSLighting ballastConsumer electronicsDVD, television, set top boxHome appliancesWasher, dryer, refrigerator, air conditioner, humidifierTip/ring - Power Cross (2AG)Target applications:AC line prote

12、ction for power supplies AC lineCommon/groundPower modulePower plugPower systemUltraMOV, CIII, LA series radial leaded MOVCartridge or leaded fuseFusePower supplyTip/ring circuitPower supply10Confidential and Proprietary to Littelfuse, Inc. 2006 Littelfuse, Inc. All rights reserved.FuseSolutions for

13、: Battery pack and DC bus overcurrent protectionSurface Mount Chip Fuse Space-efficient form factors (0402, 0603, 1206) Amperage ratings from 0.062A to 7.0A Low profile for height-sensitive applications Constructed on an epoxy-based substrate similar to the circuit board on which it will be installe

14、d. Avoids temperature coefficient of expansion (TCE) mismatch that could cause reliability problems in the field. Key feature of FR-4 substrate is higher melting i2t value than ceramic chip fuse, which minimizes nuisance tripping during in-rush current events. Lower resistance values also minimize p

15、ower dissipation. 11Confidential and Proprietary to Littelfuse, Inc. 2006 Littelfuse, Inc. All rights reserved.Solutions for: AC mains/DC bus overcurrent protection Tip/Ring circuit protectionSurface Mount Fuse Includes Nano2, TeleLink and UMF series Rated for AC and DC circuits Amperage ratings fro

16、m 0.25A to 15.0A Constructed using ceramic tube bodies to increase breaking capacity and working voltage Key features are higher melting i2t value than chip fuse, which minimizes nuisance tripping during in-rush current events; wire-in-air design minimizes thermal de-rating factor and extends usable

17、 temperature range. FuseNano2 UMF fuseTeleLink fuseNano2 fuse12Confidential and Proprietary to Littelfuse, Inc. 2006 Littelfuse, Inc. All rights reserved.Chip fusesBattery packHard disk driveCell phoneDigital cameraLCD monitor inverter (small panels)MP3/PMP playerBluetooth headsetWire-in-Air SMD fus

18、esMotherboards (servers, notebooks)LCD monitor inverter (large panels)Telecom equipment (TeleLink)Automotive Electronics modulesTelematics, climate control, navigation, body controllersTarget applications:Protection of inverter circuit (LCD)DC inputCommon/groundInverter circuitDC inputPower systemML

19、V (MLA series)Diode (SMA series)Chip fuseNano2 fuseProtection of DC bus (HDD) Data busVBUSSignal GroundHDD unitRibbon cable/ connectorMotherboard0402, 0603 MLV SMAJ diodeShield Ground0467 Pb-free0434 Pb/Sn0435 Pb-freeD0DnInverterFuseInverter13Confidential and Proprietary to Littelfuse, Inc. 2006 Lit

20、telfuse, Inc. All rights reserved.What is a FUSE?1. A fuse is a thermally responding device.2.A fuse is designed and manufactured to protect by being the intentional weak link in an electrical circuit. Purpose of the fuse is to prevent FIRE!Fusing UltimateSystem End14Confidential and Proprietary to

21、Littelfuse, Inc. 2006 Littelfuse, Inc. All rights reserved.基基 本本 保保 險險 絲絲 學學 15Confidential and Proprietary to Littelfuse, Inc. 2006 Littelfuse, Inc. All rights reserved.保保 險險 絲絲 基基 本本 工工 作作 原原 理理:結構: 金屬熔絲及兩端極金屬熔絲及兩端極功能: 保險絲是串聯在電路中保險絲是串聯在電路中,當電路正常工作時當電路正常工作時,保險絲只相當予一根導保險絲只相當予一根導線能夠長時間穩定地使用線能夠長時間穩定地使

22、用. 只有只有當電路中發生較大的過載電流和或發生短路時保險絲才會熔斷開電流來保護電路的安全.原理: 保險絲通電時因電流轉換的熱量會使熔絲的溫度上升保險絲通電時因電流轉換的熱量會使熔絲的溫度上升. 當正常工作電流當正常工作電流或允許的過載電流通過時或允許的過載電流通過時, 電流產生的熱量通過熔絲電流產生的熱量通過熔絲,殼體向周圍環境輻射殼體向周圍環境輻射, 通通過對流和傳導等方式散發的熱量能與產生的熱量逐漸達到平衡過對流和傳導等方式散發的熱量能與產生的熱量逐漸達到平衡. 當散熱速跟不上發熱時這些熱量就會在熔絲上逐漸累積,使溫度上升,一旦溫度達到和超過熔絲材料的熔點時會使熔絲熔化而斷開電流,達到保

23、護的作用.16Confidential and Proprietary to Littelfuse, Inc. 2006 Littelfuse, Inc. All rights reserved.保險絲允許的過載能力保險絲允許的過載能力(Fuse Current Capacity)Max. Carrying current:UL STD保險絲的保險絲的最大不熔斷電流是是75% In；IEC STD保險絲的保險絲的最大不熔斷電流是是100%In。同時也要求保險絲在超過限量的過載電流時能及時燒斷，其中同時也要求保險絲在超過限量的過載電流時能及時燒斷，其中:Minimum Fusing Curren

24、t:UL STD保險絲的保險絲的最小熔斷電流在在 200%In左右左右；IEC STD保險絲的保險絲的最小熔斷電流在在 210%左右。左右。ColdHOT17Confidential and Proprietary to Littelfuse, Inc. 2006 Littelfuse, Inc. All rights reserved.選選 用用 保保 險險 絲絲 的的 重重 要要 參參 數數(Fuse selection factors)選擇的保險絲是主要或次要的保護元選擇的保險絲是主要或次要的保護元件件?(Fuse for Primary or Secondary Protection?

25、)1。額定電額定電流流 (Rated current) (Minimum fuse rating)=In2。額定電壓額定電壓 (Rated voltage) AC/DC3。應用環境應用環境温度温度 (Ambient temperature)4。電壓電壓降降 (Voltage drop)5。熔。熔斷斷特性特性 (Fusing characteristics) -時間時間/電電流特性流特性(TC curves) 6。遮斷遮斷/分分斷斷能力能力 (Breaking / Interrupting Capacity)7。熔化。熔化熱熱能值能值 ( Melting It ) 8。結構結構特特徵徵 (Str

26、ucture) -外形尺寸外形尺寸 -安安裝裝型式型式18Confidential and Proprietary to Littelfuse, Inc. 2006 Littelfuse, Inc. All rights reserved.额定额定電電流流 Rated Current ( In)額定電額定電流流 In= Irmax / (Frf * Tdf)最大最大/重載工作電重載工作電流流(max operating currentIrmax*)UL re-rating factor:Frf-0.75IEC re-rating factor: Frf-1Temperature de-rati

27、ng factor, Tdf refer to temperature curve A, B or CUL規格保險絲規格保險絲： In =Ir/(Frf*Tdf)IEC規格保險絲規格保險絲: In = Ir/Tdf計算的計算的 In是是Absolute最小的最小的In額定電額定電流值可選或流值可選或往上往上選選用最用最佳適用佳適用的的In额额定定電電流值。流值。19Confidential and Proprietary to Littelfuse, Inc. 2006 Littelfuse, Inc. All rights reserved.應用環應用環境温度境温度(Ambient Temp

28、erature)UL / IEC保險絲保險絲的各项要求都的各项要求都是指在室温是指在室温條條件下件下-250C時時應用環應用環境温度境温度對保險絲對保險絲的的特性特性是有是有很大的很大的影影響響!温度折减率温度折减率-TdfAmbient Temp: refers to the air temperature immediately to the vicinity of fuse. (Note: At the worst Condition such as Burn In, high temp test, etc.)20Confidential and Proprietary to Litte

29、lfuse, Inc. 2006 Littelfuse, Inc. All rights reserved.實例:應用電壓:12 V DC應用最大/重載電流: 1A max 環境溫度緊鄰保險絲: 80C 脈衝電流: 20A 30uSec.*短路電流短路電流: 35A max. at 12V保險絲種類: 1206 size TFF應用最大電流是應用最大電流是 1.0A 就將此值帶入下述公式就將此值帶入下述公式:Tdf:0.75*(0.70)Example:21Confidential and Proprietary to Littelfuse, Inc. 2006 Littelfuse, Inc

30、. All rights reserved.Example :Steady state current22Confidential and Proprietary to Littelfuse, Inc. 2006 Littelfuse, Inc. All rights reserved. 應用最大電流(Irmax) 1.0ACat. Fuse Rating = - = - 0.75 x 溫度折減率溫度折減率(Tdf)80C 0.75 x 0.70Cat. Fuse Rating =1.91A 計算值計算值-Absolute minimum fuse rating can be selected

31、. (可從可從 1206 size 的的466 or 468系列系列2A 以上安培數以上安培數, 請參考表請參考表(一一)。)表表 (一一)P/N Rating Voltage Melting I2t0466002 2.0A 63V 0.2326A2Sec046602.5 2.5A 32 V 0.3516A2Sec0466003 3.0A 32V 0.5760A2Sec0468002 2.0A 63V 0.506A2Sec0468003 3.0A 32V 1.270A2Sec Example: (Continue)23Confidential and Proprietary to Littel

32、fuse, Inc. 2006 Littelfuse, Inc. All rights reserved.额定额定電壓電壓 Rated Voltage( Vr） 保險絲的保險絲的额定额定電壓電壓應應大大於於或等或等於於應用電應用電路路電壓電壓 (Vr標標示在保險絲目錄上示在保險絲目錄上) 正常正常負載時負載時额定额定電壓對電壓對保險絲保險絲影影響響很小很小 過載過載熔熔斷時斷時额定额定電壓電壓對對保險絲保險絲有影有影響響24Confidential and Proprietary to Littelfuse, Inc. 2006 Littelfuse, Inc. All rights rese

33、rved.FUSING Basics: Hot spot 温度温度Temperature(C) 負載電流時的溫度負載電流時的溫度 PCB Sn 锡球锡球 PCBInI In Melting Point25Confidential and Proprietary to Littelfuse, Inc. 2006 Littelfuse, Inc. All rights reserved. t = 0 t =1 fusing to meltingfusing Basic Fusing Process (保險絲熔斷過程保險絲熔斷過程) 26Confidential and Proprietary to

34、 Littelfuse, Inc. 2006 Littelfuse, Inc. All rights reserved. t =1 t =3 arcing continue depended on the I and V， Arcing end t =2, arcing starting Basic Fusing Process(保險絲熔斷過程保險絲熔斷過程) 27Confidential and Proprietary to Littelfuse, Inc. 2006 Littelfuse, Inc. All rights reserved.28Confidential and Propri

35、etary to Littelfuse, Inc. 2006 Littelfuse, Inc. All rights reserved. 保險絲的電壓降說明保險絲的電壓降說明 保險絲的電壓降是的電壓降是保險絲在額定電流條件下，其兩在額定電流條件下，其兩端的電壓降。它反映了端的電壓降。它反映了保險絲的內阻，其值不應過的內阻，其值不應過大。若將內阻（電壓降）過大的大。若將內阻（電壓降）過大的保險絲安裝在電路安裝在電路中，它將影響電路的系統參數，使得電路不能正常中，它將影響電路的系統參數，使得電路不能正常工作。標準對電壓降不僅有其值的上限規定，而且工作。標準對電壓降不僅有其值的上限規定，而且對其一致

36、性也作了規定。對其一致性也作了規定。 29Confidential and Proprietary to Littelfuse, Inc. 2006 Littelfuse, Inc. All rights reserved.時間時間/電電流特性流特性 Time/Current Characteristic 承受承受過電過電流流時時, 電電流流與熔斷時間與熔斷時間的的關係關係 It is a characteristics determine how fast a fuse responds to over-currents. Over-current is divided into overl

37、oads and short circuits. UL和和IEC的的熔斷熔斷特性是特性是完完全不同的全不同的30Confidential and Proprietary to Littelfuse, Inc. 2006 Littelfuse, Inc. All rights reserved.UL/CSA248-14規格規格UL Vs IEC60127規格（）規格（）31Confidential and Proprietary to Littelfuse, Inc. 2006 Littelfuse, Inc. All rights reserved.AGENCY APPROVALS UL /

38、CSA 248-14 Listed Complied UL/CSA248-14 Recognized - Manufacturer IEC 60127 Certify agency: VDE, BSI, SEMKO, TUV, NemKo METI PSE Marking CCC China Safety per IEC K-mark Korean Safety32Confidential and Proprietary to Littelfuse, Inc. 2006 Littelfuse, Inc. All rights reserved.時間時間 vs. 電流曲線電流曲線:(Time v

39、s. Current curve)T/C Curve是一個供是一個供設計參考用設計參考用的工具而不是保險絲的規範的工具而不是保險絲的規範是保險絲一個的是保險絲一個的平均熔斷時間曲線圖平均熔斷時間曲線圖. 實際熔斷時間必須考量實際實際熔斷時間必須考量實際供應電壓供應電壓.33Confidential and Proprietary to Littelfuse, Inc. 2006 Littelfuse, Inc. All rights reserved.如何看讀時間如何看讀時間/電流曲線電流曲線(How to read the TC curve) 先選先選 3A 曲線曲線.找出找出3曲線與曲線與

40、 6A線交叉點線交叉點.後再往後再往Y軸讀取相應時間軸讀取相應時間 - 0.1 seconds.180 1 2 3 5 7.5 1534Confidential and Proprietary to Littelfuse, Inc. 2006 Littelfuse, Inc. All rights reserved. 遮斷遮斷/分分斷斷能力能力 (Breaking/Interrupting Capacity)在額定電壓條件下,保險絲能夠安全地分斷預期的電流且沒有對環境的損害. (Interrupting rating also known as Breaking Capacity or sho

41、rt circuit rating, the interrupting rating is the maximum approved current which the fuse can SAFELY interrupt at rated voltage. )保險絲最重要的安全指標 (The word “safely” here means that there should be no significant damage to the fuse housing nor to the surroundings as a result of arcing or molten metal eme

42、rging from the fuse.)短路短路時時保險絲保險絲能安全分能安全分斷斷的最大的最大短路電短路電流流IEC STD Fuse Type有分高分斷(High Breaking Capacity)，中分斷(Enhance Breaking Capacity)和低分斷(Low Breaking Capacity)保險絲 .35Confidential and Proprietary to Littelfuse, Inc. 2006 Littelfuse, Inc. All rights reserved.遮斷遮斷/分分斷斷能力能力 (Breaking/Interrupting Capa

43、city)UL 248-14規定的分斷能力規定的分斷能力: 125VAC條件下條件下UL Listed保險絲必須能切斷保險絲必須能切斷10,000A for Subminiature fuse(2AG)的電流的電流;250VAC條件下保險絲必須能切斷的電流如下條件下保險絲必須能切斷的電流如下: 保險絲的額定電流保險絲的額定電流 額定分斷能力額定分斷能力 0 1 A 35A 1.1 3.5A 100A 3.6 9A 200A 10.1 15A 750A 15.1 30A 1500A Remark: Recognized 認證的保險絲直接參考製造商的認證的保險絲直接參考製造商的Interrupti

44、ng Rating規格規格36Confidential and Proprietary to Littelfuse, Inc. 2006 Littelfuse, Inc. All rights reserved.遮斷遮斷/分分斷斷能力能力 (Breaking/ Interrupting Capacity) IEC 127規定的分斷能力規定的分斷能力: 250VAC條件下的分斷能力保險絲條件下的分斷能力保險絲- 低分斷(LBC)必須能安全切斷必須能安全切斷35A MINIMUM或或 它的它的10In中的最中的最大的電流大的電流; 中分斷(EBC)必須能安全切斷必須能安全切斷150A的電流的電流;

45、高分斷(HBC)必須能安全切斷必須能安全切斷1500A的電流的電流37Confidential and Proprietary to Littelfuse, Inc. 2006 Littelfuse, Inc. All rights reserved.EXAMPLE: (continue) 0466 series Interrupting rating 50A 63V AC/DC for 0.5 2.0A 0466 series Interrupting rating 50A 32V AC/DC for 2.5 3A 0466 series Interrupting rating 50A 24

46、V AC/DC for 4 5A 0468 series Interrupting rating 35A 63V AC/DC for 2A 0468 series Interrupting rating 50A 32V AC/DC for 3A38Confidential and Proprietary to Littelfuse, Inc. 2006 Littelfuse, Inc. All rights reserved.熔化熔化熱熱能值能值 (Melting I2t )切切斷保險絲斷保險絲所需的所需的熱熱能量值能量值* (is a direct measure for the energ

47、y required to blow the fuse-element.) often, the fuse nominal melting It Method of fuse selection is applied to those applications in which the fuse MUST sustain large current pulses of a short duration. 選選用用保險絲保險絲规格的重要参数规格的重要参数(most important fuse selection factor) 防疲勞防疲勞, 多次的擴散多次的擴散, 氧化氧化 ( preven

48、t de-grade, and oxidize, etc.)力特對每一種小型保險絲给出了Fuse Nominal熔化I2t值清除I2t = 熔化I2t + 飛弧I2t Clearing I2t =Melting I2t +Arcing I2t *Ratio 22% =Pulse I2t / Fuse Melting I2t *Select either F-fast-acting or T-time lagged fuse* These high-energy currents are common in many applications and are described by a var

49、iety of terms, such as “surge current”, “ start-up current”, “ Inrush current”, and other similar circuit “ transients” that can be classified in general category of “ PULSES.” Pulse current i.e. a flow of repetitive current pulses.39Confidential and Proprietary to Littelfuse, Inc. 2006 Littelfuse,

50、Inc. All rights reserved. Pulse It = ip(t)dt = ip(t) 0Safety factor is Less than 22% = Pulse It / Fuse Nominal Melting ItOR Fuse minimum Melting It = Pulse It / 22%40Confidential and Proprietary to Littelfuse, Inc. 2006 Littelfuse, Inc. All rights reserved.I2t of an Arbitrary Pulse - ConceptuallyI2t

51、 = area under i2(t) curvei(t)Time (t)Current (A)i2(t)Time (t)Current (A)i2(t)41Confidential and Proprietary to Littelfuse, Inc. 2006 Littelfuse, Inc. All rights reserved.Melting I2tMelting I2t is an index that characterizes the energy required to melt a fuse element.Melting I2t values are empiricall

52、y measured as shown:Current (A)Timemelting timearcing timeElement melted,Arcing beginsIntegrated to calculateMelting I2t42Confidential and Proprietary to Littelfuse, Inc. 2006 Littelfuse, Inc. All rights reserved.Example of Inrush CurrentIp2Ip1Ip3t1t2t3t4t5Ir=4.5A43Confidential and Proprietary to Li

53、ttelfuse, Inc. 2006 Littelfuse, Inc. All rights reserved.Example of InrushIp1= 25AIp2 = 20AIp3 = 25AT1= 3mSecT2 = 10SecT3 = 3mSecT4 = 1hourT5 = 5mSecPulse I2t1= Ip1 x Ip1 x t1 = 25 x 25 x 3mSec=1.875A2SecPulse I2t2 = Ip2 x Ip2 x (t3-t2) = 20 x 20 x 3mSec = 1.2A2Sec.Pulse I2t3 = Ip3 x Ip3 x ( t5 t4)

54、= 25A x 25A x 5mSec=3.125A2SecTotal Pulse I2t = 6.2A2Sec (3.1A2Sec)Fuse Melting I2t= Total Pulse I2t / 0.22 100,000 cycles=28.2A2Sec(14.1A2Sec)Fuse rating, In = Ir / (safety factor * Temperature factor)UL factor= 0.75, IEC factor= 1, Temperature=100CFuse rating, In = 4.5 / ( 0.75 x0.9) = 6.67A for U

55、L type fuse minimum.In= 4.5 / ( 1 x 0.9) = 5A for IEC type minimum.44Confidential and Proprietary to Littelfuse, Inc. 2006 Littelfuse, Inc. All rights reserved.Example (continue) : Pulse I2t calculationT：30sec Ip：Max 20APulse I2t=（Ip2T）（）（20 20 30sec）= 0.12A2Sec (Assume worst inrush condition of Squ

56、are waveform*)100000Pulses Factor：0.22 safety factor Fuse Melting I2t= Pulse I2t / 0.22 = 0.12 / 0.22= 0.5455A2Sec 45Confidential and Proprietary to Littelfuse, Inc. 2006 Littelfuse, Inc. All rights reserved.Calculated Pulse I2t(計算單脈衝I2t值) = (20A)2 x 30uSec=0.12A2Sec / 2 = 0.06A2Sec(請參照LFs Designers

57、 Guide waveform C, on page 6, chart I,如下Note: 最佳以方形波計算單脈衝Pulse I2t值) CCalculated Melting I2t(計算熱熔能量值計算熱熔能量值I2t) = 0.12 0.22 = 0.5455A2Sec* ( Per “A”)=0.06 / 0.22 = 0.273A2Sec* (Per “C”) % ratio = 0.06 / 0.2326 =0.258 = 25.8% -NG (52%) % ratio = 0.06 / 0.3516 = 0.171 = 17.1% -OK(34.2%) % ratio = 0.06

58、 / 5716 = 0.105 = 10.5% -OK(21%) % ratio = 0.06 / 506 = 0.119 = 11.9% -OK(23.8%) % ratio = 0.06 / 1.27 = 0.048 = 4.8% -OK(9.5%) Example (Continue): Pulse I2T & Melting I2t46Confidential and Proprietary to Littelfuse, Inc. 2006 Littelfuse, Inc. All rights reserved.( 設計能耐100,000 pulses per Chart I

59、I by 22% or less, on page 6如下) 22%Example (Continue)47Confidential and Proprietary to Littelfuse, Inc. 2006 Littelfuse, Inc. All rights reserved. Nuisance opening is most often caused by incomplete analysis of the circuit under consideration. Special attention must given to normal operating current,

60、 ambient temperature, and pulses. For trouble-free, long-life fuse protection, it is good design practice to select a fuse such that the It of the waveform is no more than 20% of the nominal melting It rating of the fuse.48Confidential and Proprietary to Littelfuse, Inc. 2006 Littelfuse, Inc. All rights reserved.Tran