基于AT89C51單片機的數(shù)字電壓表設(shè)計

1、基于單片機的led顯示屏的數(shù)字電壓表 引言這是一個很容易建立并且非常準(zhǔn)確和有用的數(shù)字電壓表。它被設(shè)計成一個面板儀表，可用于直流電源供應(yīng)器或其他需要有一個準(zhǔn)確電壓指示的地方。該電路采用的adc（模擬數(shù)字轉(zhuǎn)換器）集成電路cl7107由intersil公司生產(chǎn)。該ic采用40引腳的情況下整合了所有必要的電路模擬信號轉(zhuǎn)換為數(shù)字，可以直接驅(qū)動4個7段led顯示。在ic中內(nèi)置的電路是數(shù)字轉(zhuǎn)換器，比較器，一個時鐘，一個解碼器和一個7段led顯示驅(qū)動器模擬。在這里它描述了一個可以顯示在0-1999電壓范圍的直流電壓電路。前面led顯示屏數(shù)字電壓表技術(shù)規(guī)格 - 特征電源電壓：.+ / - 5v（對稱）。電源要求

2、：.200ma（最大）。測量范圍：.+ / - 0-1,999v在四個范圍。精度：.0.1。特征：- 小尺寸。- 簡易建筑。- 成本低。- 簡單的調(diào)整。- 易于讀取距離。- 很少的外部元件。數(shù)字電壓表的基本原則為了了解電路的運作的原則，說明adc的集成電路工程是必要的。該集成電路具有以下非常重要的特點：- 準(zhǔn)確性。- 抗干擾性。- 無需要一個采樣保持電路。- 它有一個內(nèi)置的時鐘。- 它不需要精度高的外部元件。一個模擬數(shù)字轉(zhuǎn)換器(adc)，從現(xiàn)在起更好的稱為雙斜率轉(zhuǎn)換器或集成轉(zhuǎn)換器。這種類型的轉(zhuǎn)換器通常優(yōu)于其他類型，因為它提供了準(zhǔn)確，簡潔的設(shè)計和它可以將相對不重要的噪音變得非?？煽?。如果將電路分

3、兩個階段描述，該電路的操作將更好的理解。在第一階段的輸入集成電壓和最后階段的輸出集成電壓中有一個電壓與輸入電壓成正比。在預(yù)設(shè)的時間結(jié)束時，積分將到達(dá)內(nèi)部基準(zhǔn)電壓以及輸出電路會逐漸降低直至達(dá)到零參考電壓水平。第二個階段就是所謂的負(fù)斜率時期，其持續(xù)時間由第一階段積分器輸出而定。作為第一個操作時間是固定的，第二個變量的長度就可以比較兩個這樣的輸入電壓，其實是相對于內(nèi)部參考電壓，其結(jié)果是編碼，然后發(fā)送到顯示。示意圖（固定16-11-09）7段顯示器引出線man6960這一切聽起來很容易，但實際上它是一系列非常復(fù)雜的操作，這些都是由adc集成電路作出了很少的外部元件，幫助它們用來配置工作的電路。詳細(xì)的電

4、路的工作原理如下。為了進(jìn)行測量，需要將電壓施加于電路的1和2點，最后通過電路的r3，r4和c4應(yīng)用到集成電路的引腳30和31。從下圖你可知這是該集成電路的輸入(分別為高與低)。r1電阻的c1一起用來設(shè)置內(nèi)部振蕩器(時鐘)，該設(shè)置約48hz。在這個時鐘速率大約有三個不同的每秒讀數(shù)。連接集成電路引腳33和34之間的電容已被選定，以彌補由內(nèi)部參考電壓帶來的誤差，并保持穩(wěn)定的顯示。電容c3和電阻r5在一起的電路是輸入電壓的集成電路，同時它可避免任何使電路更快的分裂輸入電壓，從而使錯誤的可能性大大減少進(jìn)而使電路更穩(wěn)定。在沒有輸入電壓時電容器c5強迫儀器顯示為零。當(dāng)輸入為零時電阻r2和p1一起用來調(diào)整儀器

5、在設(shè)置過程中顯示為零。電阻r6的控制電流允許流經(jīng)顯示，以便使電路在沒有損壞的前提下顯示充分的亮度。至于我們上面已經(jīng)提到的芯片它能夠驅(qū)動4個共陽極led顯示屏。這三個最右邊的顯示器相連，使他們可以顯示所有從0到9的數(shù)字，而從左邊第一個只能顯示數(shù)字1，當(dāng)電壓為負(fù)“-”的時候。整個電路工作，從對稱5伏直流電電源，這在引腳1(+5v)申請，21(0v)，26(-5v)集成電路。背面單片機自身的抗干擾措施為提高單片機自身的可靠性，近年來單片機的制造商在單片機設(shè)計上采取了一系列措施來提高可靠性。這些技術(shù)主要體現(xiàn)在以下幾方面：1.降低外部時鐘頻率外部時鐘是高頻的噪聲源，除了能對本應(yīng)用系統(tǒng)引起干擾之外，還可能

6、產(chǎn)生對外界的干擾，使電磁兼容檢測不能達(dá)標(biāo)。在對系統(tǒng)可靠性要求很高的應(yīng)用系統(tǒng)中，選用頻率低的單片機是降低系統(tǒng)噪聲的原則之一。以8051單片機為例，最短指令周期1s，這時外部時鐘是12mhz。而同樣速度的motorola單片機系統(tǒng)時鐘只需4mhz，更適合工業(yè)控制系統(tǒng)使用。近年來，一些生產(chǎn)8051兼容單片機的廠商也采用了一些新技術(shù)，在不犧牲運算速度的前提下將對外部時鐘的需求降至原來的1/3。而motorola單片機在新推出的68hc08系列以及其16/32位單片機中普遍采用了內(nèi)部鎖相環(huán)技術(shù)，使得外部時鐘頻率降至32khz，而內(nèi)部總線速度卻提高到8mhz甚至更高。2.低噪聲系列單片機傳統(tǒng)集成電路的設(shè)計

7、中，通常將電源、地的引出安排在對稱的兩邊。如左下角是地，右下角是電源，這使得電源噪聲穿過整個硅片。改進(jìn)的技術(shù)將電源、地安排在兩個相鄰的引腳上，這樣一方面降低了穿過整個硅片的電流，一方面更容易在pcb的設(shè)計上安排外部去耦電容，以降低系統(tǒng)噪聲。另一個在集成電路設(shè)計上降低噪聲的例子是驅(qū)動電路的設(shè)計。一些單片機提供若干個大電流的輸出引腳，從幾十毫安到數(shù)百毫安。這些大功率的驅(qū)動電路集成到單片機內(nèi)部無疑是增加了噪聲源。而跳變沿軟化技術(shù)可消除這方面的影響，辦法是將一個大功率管做成若干個小管子的并聯(lián)，再為每個管子的輸出端串聯(lián)不同等效阻值的電阻。這些是為了降低di/dt。3.時鐘監(jiān)測電路、看門狗技術(shù)與低電壓復(fù)位

8、當(dāng)發(fā)現(xiàn)系統(tǒng)時鐘停振時，通過監(jiān)測系統(tǒng)時鐘產(chǎn)生系統(tǒng)復(fù)位信號可以恢復(fù)系統(tǒng)時鐘，這是單片機提高系統(tǒng)可靠性的措施之一。而時鐘監(jiān)控有效與省電指令stop是一對矛盾，只能使用其中之一?？撮T狗技術(shù)是用來監(jiān)測應(yīng)用程序中一段定時中斷服務(wù)程序的運行狀況的，當(dāng)這段程序不工作時判斷為系統(tǒng)故障，從而產(chǎn)生系統(tǒng)復(fù)位。低電壓復(fù)位技術(shù)是用來監(jiān)測單片機電源電壓的，當(dāng)電壓低于某一值時產(chǎn)生復(fù)位信號。由于單片機技術(shù)的發(fā)展，單片機本身對電源電壓范圍的要求越來越寬。電源電壓從原來的5v下降至3.3v，并繼續(xù)下降到2.7v、2.2v、1.8v。是否使用低電壓復(fù)位功能應(yīng)根據(jù)具體應(yīng)用情況進(jìn)行權(quán)衡。用于單片機系統(tǒng)的干擾抑制元件1.去耦電容每個集成電

9、路的電源、地之間都應(yīng)該配置一個去耦電容，它可以濾掉來自電源的高頻噪聲。作為儲能元件，它吸收該集成電路內(nèi)部三極管導(dǎo)通、截止引起的電流變化(di/dt)或是提供三極管導(dǎo)通、截止所需的變化電流，從而降低系統(tǒng)噪聲。要選用高頻特性好的獨石電容或瓷片電容作去耦電容。每塊印制電路板上電源引入的地方要安放一只大容量的儲能電容。由于電解電容的纏繞式結(jié)構(gòu)，其分布電感較大，對濾除高頻干擾信號幾乎不起作用，使用時要與去耦電容成對使用。鉭電容的使用效果相對電解電容更好。2.抑制高頻電感用粗漆包線穿入軸向有幾個孔的鐵氧體芯，就構(gòu)成了高頻扼制器件。將其串入電源線或地線中可以阻止高頻信號從電源/地線引入。這種元件特別適用于隔

10、開一塊印制電路板上的模擬電路區(qū)、數(shù)字電路區(qū)、以及大功率驅(qū)動區(qū)的供電。必須注意的是它必須放在該區(qū)儲能電容與電源之間而不能放在儲能電容與用電器件之間。3.自恢復(fù)保險絲這是用一種新型高分子聚合材料制成的器件，當(dāng)電流低于其額定值時，它的直流電阻只有零點幾個歐姆。而隨著電流大到一定程度，它的阻值也迅速升高，引起發(fā)熱，而越熱電阻值就越大，從而阻斷電源電流。當(dāng)溫度降下來以后能自動恢復(fù)正常。這種器件可防止cmos器件在遇到強烈的沖擊干擾時引起的所謂“可控硅觸發(fā)”現(xiàn)象。這種現(xiàn)象是指集成電路硅片的基體變得導(dǎo)通，從而引起電流增大，導(dǎo)致cmos集成電路發(fā)熱乃至燒毀。4.靜電放電搶靜電放電槍是一個相對便宜的可以幫助發(fā)現(xiàn)

11、數(shù)字電路中的高頻感應(yīng)性的工具。使用這種槍最初是為了保證設(shè)計不會被高壓靜電損毀。高壓靜電由人體產(chǎn)生在接觸時產(chǎn)生放電。我們可以得到電池供電的便攜式靜電放電槍，且通過編程智能地設(shè)定不同的工作電壓數(shù)量級。因為便攜性，ems槍可以用在許多應(yīng)用的免疫性能測試中。esd槍通常為用戶提供了兩種類型的尖端：空氣放電尖端和接觸放電尖端?？諝夥烹娂舛耸乔蛐蔚?，然而接觸放電尖端是錐形的。使用接觸放電，尖端可以放在pcb導(dǎo)線或者器件的引腳上，然后可以按下esd槍觸發(fā)器。大多數(shù)的esd槍限制了接觸放電的電壓為8kv。在電源線和外部連接上使用接觸放電可以找到任何設(shè)計缺陷。一般的步驟是將尖端連接到導(dǎo)線上，當(dāng)應(yīng)用系統(tǒng)在運行的時

12、候，發(fā)射隨機噪聲尖峰，其初始值小于1kv，提高電壓直到故障發(fā)生?？諝夥烹娍梢詮?kv到小于25kv進(jìn)行設(shè)置，這只能應(yīng)用在外部連接。這種類型的esd測試通常用在遭受esd放電的區(qū)域，這種放電是由于充電的人靠近設(shè)備引起的。這種類型的esd測試可以引起重復(fù)性的問題，這種重復(fù)性的問題是由尖端采用的角度和尖端靠近放電部位的速度引起的。在內(nèi)部引腳和mcu引腳上應(yīng)用空氣esd會造成破壞，因此只推薦在pcb和遭受由人引起的esd的區(qū)域使用。5.防雷擊裝置室外使用的單片機系統(tǒng)或者電源線、信號線是從室外架空引入室內(nèi)的單片機系統(tǒng)，要考慮系統(tǒng)的防雷擊問題。常用的防雷擊器件有：氣體放電管，瞬態(tài)電壓抑制器tvs(tran

13、sient voltage supervention)等。氣體放電管在電源電壓大于某一值時，此值通常為數(shù)十伏或數(shù)百伏，放電擊穿氣體，將電源線上的強沖擊脈沖導(dǎo)入大地，tvs可以看成是兩個方向相反的齊納二極管的并聯(lián)，當(dāng)電兩端電壓高于某一額定值時導(dǎo)通。其特點是可以瞬態(tài)通過數(shù)百乃至上千安培的電流。這類元器件與抗共模和抗差模干擾的電感配合使用才可以提高抗干擾效果。數(shù)字電壓表印刷電路板的加工首先讓我們考慮建立一個印刷電路板上的電子電路的基礎(chǔ)知識。該印刷電路板是由薄絕緣銅的導(dǎo)電復(fù)合材料薄層形成，這樣以形成電路之間的各組成部分的必要的導(dǎo)體。一個設(shè)計完善的印刷電路板是非?？扇〉模驗樗蟠蠹涌炝思庸?，并大大減少

14、了決策失誤的可能性。為了保護(hù)印刷電路板在存儲過程中被氧化和保證它到達(dá)你所要求的完美的條件，在生產(chǎn)過程中將銅鍍錫的同時起表面還要覆蓋一層特殊的漆，這樣不僅防止了它被氧化，也使焊接更容易。焊接的部件，印刷電路板是建立你的電路的唯一的方式和你在做板時很大程度上取決了你的成功或失敗。這項工作也并不是很困難，如果你堅持有一些規(guī)則你應(yīng)該沒有問題。在你使用電烙鐵時，其功率不應(yīng)超過25瓦。它的尖應(yīng)該是好的，并且必須時刻保持清潔。為此我們特地準(zhǔn)備了一特制海綿并使其保持潮濕，這樣可以不時擦拭熱烙鐵尖，從而去除積累在它上面的殘渣。如果烙鐵尖不能清洗或更換，請勿用文件或砂紙弄臟或磨損其尖部。在市場上有許多不同類型的焊

15、接劑，你應(yīng)該選擇一個優(yōu)質(zhì)的一個在其核心包含必需的流量的焊接劑，以保證每次焊接時都能完美的接合。不使用助焊劑除了在你的焊接劑里已含有助焊劑。太多的流量可能會導(dǎo)致許多問題，也是電路故障的主要原因之一。但如果您必須使用額外的流量，因為它是在你不得不將銅線鍍錫的情況下，將起徹底清除干凈后你完成了你的工作。為了焊接組件正確，您應(yīng)該執(zhí)行下列操作：- 用一小塊砂紙清潔清潔組件。- 彎曲組件使它們之間有一合適的距離并插入在印刷電路板中的正確地位組成部分。- 你有時可能會發(fā)現(xiàn)比起平常還會有重計部分，它將過于厚而不能進(jìn)入個人電腦印刷電路板的孔。在這種情況下使用的小型鉆孔略有放大。不要使孔太大，因為這將會使焊接困難

16、。安置部分印刷電路板尺寸：77,6毫米 44,18毫米或35的范圍內(nèi)做拿著熱鐵將其尖端放在組件的一角上，同時將焊錫絲末梢放在尖端的一個點上。烙鐵頭必須觸及略高于印刷電路板的地方。當(dāng)焊錫絲開始融化和流動等待它均勻覆蓋孔周圍的區(qū)域和通量癤并且焊料從下面流出。整個過程不應(yīng)超過5秒。清除烙鐵，讓焊接劑自然冷卻不吹，或移動組件。如果一切處理得當(dāng)則表面聯(lián)合處有一個光明的金屬質(zhì)感，其邊緣應(yīng)該是平滑的并且有一軌道面。如果焊料看起來暗淡無光，有裂痕的，或有一個氣泡的形狀，那么你虛焊了和你應(yīng)該清除焊接劑(用泵，或焊芯)然后重做它。注意不要過熱的軌道，因為它是很容易從其電路板上解除從而損壞電路板。在你焊接一個敏感元

17、件時，很好的做法是用一個長鼻子鉗子夾著電路板組件的邊緣進(jìn)行熱轉(zhuǎn)移但是那樣容易損壞組件。確保你不使用過多的焊料是必需的，因為你正在冒著毗鄰軌道短路的風(fēng)險，特別是如果他們都非常接近時。當(dāng)你完成你的工作時，切斷組件的多余部分和用適當(dāng)?shù)娜軇﹣韽氐浊宄赡苓€留在電路板上的助焊劑殘留物。更換的電阻按照下表：0 - 2v. r3 = 0歐姆10 - 20v. r3 = 1.2千歐10 - 200v. r3 = 12千歐10 - 2000v. r3 = 120千歐1當(dāng)您完成所有的電路板上焊接和您確信一切正常，可以插入在其位芯片。該ic是cmos類型于是對靜電非常敏感。它有鋁箔包裹以防止靜電放電，并應(yīng)小心處理，

18、以免損壞它。盡量避免用你的手接觸引腳，并且保持地面電路和你的身體電位在你插入的位置。電路連接到一個合適的電源5伏直流電上，開啟電源。在光顯示區(qū)應(yīng)立即形成一個數(shù)字。短路輸入（0v）和調(diào)整微調(diào)小屏幕顯示，直到完全去掉0。零件清單r1=180kp1=2萬多轉(zhuǎn)微調(diào)r2=22ku1=icl7107r3=12kld1，2,3,4=man6960共陽極led顯示屏r4=1mr5=470kr6=560 ohmc1=100pfc2,c6,c7=100nfc3=47nfc4=10nfc5=220nf故障檢查簡介檢查您可能造成的虛焊，跨越鄰近軌道或助焊劑殘留物的橋梁工作，通常會造成問題。再次檢查所有的電路和外部連接

19、，看看是否有一個錯誤?？词欠裼腥魏谓M件丟失或錯誤的地方插入：- 確保所有的兩極分化組件已被焊接正確。- 確保供應(yīng)具有正確的電壓，以正確的方式連接到你的電路上。- 檢查您的故障或損壞的部件項目。樣品電源1樣品電源2led display digital voltmeter based on mcufront sidecopyright of this circuit belongs to smart kit electronics. in this page we will use this circuit to discuss for improvements and we will intr

20、oduce some changes based on original schematicgeneral description this is an easy to build, but nevertheless very accurate and useful digital voltmeter. it has been designed as a panel meter and can be used in dc power supplies or anywhere else it is necessary to have an accurate indication of the v

21、oltage present. the circuit employs the adc (analogue to digital converter) i.c. cl7107 made by intersil. this ic incorporates in a 40 pin case all the circuitry necessary to convert an analogue signal to digital and can drive a series of four seven segment led displays directly. the circuits built

22、into the ic are an analogue to digital converter, a comparator, a clock, a decoder and a seven segment led display driver. the circuit as it is described here can display any dc voltage in the range of 0-1999 volts. technical specifications - characteristicssupply voltage: . +/- 5 v (symmetrical)pow

23、er requirements: . 200 ma (maximum)measuring range: . +/- 0-1,999 vdc in four rangesaccuracy: . 0.1 %features- small size - easy construction - low cost.- simple adjustment.- easy to read from a distance.- few external components. how it works in order to understand the principle of operation of the

24、 circuit it is necessary to explain how the adc ic works. this ic has the following very important features: - great accuracy.- it is not affected by noise.- no need for a sample and hold circuit.- it has a built-in clock.- it has no need for high accuracy external components.schematic (fixed 16-11-

25、09)7-segment display pinout man6960an analogue to digital converter, (adc from now on) is better known as a dual slope converter or integrating converter. this type of converter is generally preferred over other types as it offers accuracy, simplicity in design and a relative indifference to noise w

26、hich makes it very reliable. the operation of the circuit is better understood if it is described in two stages. during the first stage and for a given period the input voltage is integrated, and in the output of the integrator at the end of this period, there is a voltage which is directly proporti

27、onal to the input voltage. at the end of the preset period the integrator is fed with an internal reference voltage and the output of the circuit is gradually reduced until it reaches the level of the zero reference voltage. this second phase is known as the negative slope period and its duration de

28、pends on the output of the integrator in the first period. as the duration of the first operation is fixed and the length of the second is variable it is possible to compare the two and this way the input voltage is in fact compared to the internal reference voltage and the result is coded and is se

29、nd to the display.back sidescms own anti-jamming measuresto improve the reliability of its own microcontroller. in recent years, in single-chip microcontroller manufacturers to take a series of measures designed to improve reliability. these techniques are mainly embodied in the following aspects. 1

30、. reduce the external clock frequency external clock is a high-frequency noise sources, in addition to this application systems can cause interference, the right may also be generated from outside interference and electromagnetic compatibility testing so that compliance can not be. system reliabilit

31、y in the demanding applications, the use of scm is to reduce low frequency noise of the principles of the system. in 8051, for example, the shortest 1s instruction cycle, the external clock is 12mhz. while at the same speed of the motorola mcu system clock only 4mhz, more suitable for industrial con

32、trol systems. in recent years, some of the production 8051-compatible microcontroller manufacturers have also adopted a number of new technologies, without sacrificing speed of operation under the premise of the external clock needs by up to 1/3. the motorolas 68hc08 microcontroller family in the ne

33、w release and its 16/32 bit microcontroller widely used in the internal phase-locked loop technology, the external clock frequency down to 32khz, while the internal bus speed is increased to even higher 8mhz .2. low noise series mcu traditional ic design, in the power, ground leads usually be arrang

34、ed symmetrically on both sides. if the bottom left corner is, the bottom right corner is the power supply. this makes the power supply noise across the entire wafer. improved technology will power, to arrange the two adjacent pins on the one hand, this reduces the current through the silicon, on the

35、 one hand an external decoupling capacitor in the pcb design is more easily arranged, in order to reduce system noise . another noise reduction in integrated circuit design example is the drive circuit design. some microcontroller provides a number of large current output pin, from the tens of ma to

36、 hundreds of milliamps. these high-power drive circuit integrated into the mcu will undoubtedly increase the internal noise source. the softening of hopping along the technology can eliminate the impact of this by way of a high-power tube made of a number of small tubes in parallel, and then pipe th

37、e output for each string of different equivalent resistance of the resistor. to reduce the di / dt. 3. clock monitor circuit, watchdog technology and low-voltage reset monitoring the system clock, it became apparent that the system clock to stop vibration generated when the system reset signal in or

38、der to restore the system clock is the scm one of the measures to improve system reliability. the clock monitoring of effective and energy-saving instruction stop is a contradiction. can only use one of them. watchdog technology is to monitor the application of a timer interrupt service routine of o

39、perating conditions, when this program is not working to determine the system failure, resulting in a system reset. low-voltage reset microcontroller technology is the monitoring of power supply voltage, when the voltage falls below a certain value generated reset signal. since the development of si

40、ngle chip microcomputer, microcontroller itself, the power have become increasingly demanding a wide voltage range. the original power supply voltage from 5v down to 3.3v and continue down to 2.7v, 2.2v, 1.8v. on whether the use of low-voltage reset function shall be based on the specific applicatio

41、n to weigh. 4. eft technology the newly launched motorola m68hc08 series mcu uses eft (electrical fast transient) technology to further improve anti-jamming capability of the microcontroller. when the oscillator circuit sine wave signal from outside interference, its waveform will be superimposed on

42、 a number of glitches. schmitt circuit to its shaping, this glitch will become a trigger signal interfered with the normal clock signal. alternate use of schmitt circuit and rc filter can make this glitch does not work, this is the eft technique. as vlsi technology continues to evolve, the circuits

43、internal anti-jamming technology has been developing. 5. software measures mcu instruction itself also has some anti-jamming design considerations. illegal instruction illegal instruction reset or interrupt is encountered while running the program when an illegal instruction or an illegal address sp

44、ace can generate reset or interrupt. microcomputer application system program is written in advance, there can be no illegal instruction or address. the system must be subject to interference, cpu read instruction wrong. mentioned above, is currently widely used microcontroller should have an intern

45、al anti-interference measures. in the selection of scm, it is necessary to check whether the performance of all of these in order to design a highly reliable system.in the application of software design, designers have their own experience. here we must remind the rom is the final right not to do tr

46、eatment. principle is the case here since the resumption of proceedings fall. scm systems for interference suppression components1. decoupling capacitor each ic power, ground should be configured between a decoupling capacitor, which can filter out high frequency noise from the power supply. as the

47、energy storage components, which absorb or provide the ic transistor conduction cut-off due to current changes (di / dt), thus reducing system noise. to select high-frequency characteristics of a good monolithic capacitor or porcelain capacitors for decoupling capacitors. each printed circuit board

48、power supplies should be placed where the introduction of a large-capacity storage capacitor. as the electrolytic capacitors winding structure, the distribution of a larger inductance, for filtering high-frequency interference signal is almost does not work. when used with the decoupling capacitor p

49、airs. tantalum capacitors are better than electrolytic capacitors. 2. suppress high-frequency inductance enameled wire with thick axial penetration of the ferrite core has several holes, they constitute a high-frequency devices to deter. its power cord or string into the ground can be prevented high

50、-frequency signal from the power / ground to introduce. this device particularly suitable for separating a printed circuit board area of analog circuit, digital circuit areas, and high-power-driven power supply area. it should be noted is that it must be placed in the area between the energy storage

51、 capacitor and the power can not be placed between the energy storage capacitor and the electrical device. 3. pptc this is a new type of polymer material of the device, when the current is below its rated value, its dc resistance is only a few european 12:00. the current is large to a certain extent

52、, its resistance increased rapidly, causing fever, and the more the greater the thermal resistance, thus choking off the supply current. when the temperature down to be able to automatically return to normal. this device prevents the cmos devices in the face of strong impact-type interference caused

53、 by so-called scr triggering phenomenon. this phenomenon refers to the matrix of silicon integrated circuits has become conduction, causing current increases, leading to fever and even the burning of cmos integrated circuits. 4. esd gunan electrostatic discharge (esd) gun is a relatively inexpensive

54、 tool that will help find any high-frequency susceptibility in any digital circuit. use of this gun is designed primarily to ensure that designs are not damaged with the high static voltages humans generate and discharge onto applications by contact. the esd gun is available in battery-powered porta

55、ble form and can be intelligently programmed to different voltage magnitudes. because of its portability, the esd gun can be used in many applications to test immunity performance. the esd gun normally provides the user with two types of tips: air-discharge and contact-discharge. the air-discharge t

56、ip usually is spherical, whereas the contact-discharge tip is conical to a point.using contact discharge, the tip can be placed on a pcb track or device pin, and then the gun trigger can be pressed. most esd guns will limit the contact discharge to 25 kv, which should be applied only to external connections. this type of esd testing is applied usually to areas where the application will be subject to esd discharges caused by charged humans approaching the equipment. this type of esd testing can cause repeatability problems due to the angle of