PCB 被動(dòng)組件的隱藏特性解析 傳統(tǒng)上，EMC一直被視為「黑色魔術(shù)（black magic）」。其實(shí)，EMC是可以藉由數(shù)學(xué)公式來(lái)理解的。不過(guò)，縱使有數(shù)學(xué)分析方法可以利用，但那些數(shù)學(xué)方程式對(duì)實(shí)際的EMC電路設(shè)計(jì)而言，仍然太過(guò)復(fù)雜了。幸運(yùn)的是，在大多數(shù)的實(shí)務(wù)工作中，工程師并不需要完全理解那些復(fù)雜的數(shù)學(xué)公式和存在于EMC規(guī)范中的學(xué)理依據(jù)，只要藉由簡(jiǎn)單的數(shù)學(xué)模型，就能夠明白要如何達(dá)到EMC的要求。本文藉由簡(jiǎn)單的數(shù)學(xué)公式和電磁理論，來(lái)說(shuō)明在印刷電路板（PCB）上被動(dòng)組件（passivecomponent）的隱藏行為和特性，這些都是工程師想讓所設(shè)計(jì)的電子產(chǎn)品通過(guò)EMC標(biāo)準(zhǔn)時(shí)，事先所必須具備的基本知識(shí)。導(dǎo)線和PCB走線導(dǎo)線（wire）、走線（trace）、固定架……等看似不起眼的組件，卻經(jīng)常成為射頻能量的最佳發(fā)射器（亦即，EMI的來(lái)源）。每一種組件都具有電感，這包含硅芯片的焊線（bond wire）、以及電阻、電容、電感的接腳。每根導(dǎo)線或走線都包含有隱藏的寄生電容和電感。這些寄生性組件會(huì)影響導(dǎo)線的阻抗大小，而且對(duì)頻率很敏感。依據(jù)LC 的值（決定自共振頻率）和PCB走線的長(zhǎng)度，在某組件和PCB走線之間，可以產(chǎn)生自共振（self-resonance），因此，形成一根有效率的輻射天線。在低頻時(shí)，導(dǎo)線大致上只具有電阻的特性。但在高頻時(shí)，導(dǎo)線就具有電感的特性。因?yàn)樽兂筛哳l后，會(huì)造成阻抗大小的變化，進(jìn)而改變導(dǎo)線或PCB 走線與接地之間的EMC 設(shè)計(jì)，這時(shí)必需使用接地面（ground plane）和接地網(wǎng)格（ground grid）。導(dǎo)線和PCB 走線的最主要差別只在于，導(dǎo)線是圓形的，走線是長(zhǎng)方形的。導(dǎo)線或走線的阻抗包含電阻R和感抗XL = 2πfL，在高頻時(shí)，此阻抗定義為Z = R + j XL j2πfL，沒有容抗Xc = 1/2πfC存在。頻率高于100 kHz以上時(shí)，感抗大于電阻，此時(shí)導(dǎo)線或走線不再是低電阻的連接線，而是電感。一般而言，在音頻以上工作的導(dǎo)線或走線應(yīng)該視為電感，不能再看成電阻，而且可以是射頻天線。
標(biāo)簽： PCB 被動(dòng)組件
上傳時(shí)間： 2013-10-09
上傳用戶：時(shí)代將軍
Abstract: There are differences between the operation of low-frequency AC transformers and electronic transformersthat supply current to MR16 lamps, and there are also differences in the current draw for MR16 halogen lamps andMR16 LED lamps. These contrasts typically prevent an MR16 LED lamp from operating with most electronictransformers. This article explains how a high-brightness (HB) LED driver optimized for MR16 lamps will allow LEDlamps to be compatible with most electronic transformers.A similar version of this article appeared on Display Plus, July 7, 2012 and in German in Elektronikpraxis, October 1,2012.
標(biāo)簽： LED MR 16 驅(qū)動(dòng)
上傳時(shí)間： 2013-10-14
上傳用戶：playboys0
Abstract: We don't expect manufacturers to produce clothes that in one size that fits everyone. In thesame way, one ESD component can't solve all issues—each application has different ESD requirements.Knowing that "one size fits all" cannot apply to power design, the power designer, or the engineering"super hero," must consider all the potential disruptions to a steady flow of power and thenvarious waysto mitigate them. This tutorial describes voltage- and current-limiting devices and risetime reducers tomanage the power. It also points to free and low-cost software tools to help design lowpass filters, checkcapacitor self-resonance, and simulate circuits.
標(biāo)簽： 電源工程師 電路設(shè)計(jì)
上傳時(shí)間： 2013-11-18
上傳用戶：zhouxuepeng1
Automobile electronic systems place high demands ontoday’s DC/DC converters. They must be able to preciselyregulate an output voltage in the face of wide temperatureand input voltage ranges—including load dump transientsin excess of 60V and cold crank voltage drops to 4V. Theconverter must also be able to minimize battery drain inalways-on systems by maintaining high effi ciency over abroad load current range. Similar demands are made bymany 48V nonisolated telecom applications, 40V FireWireperipherals and battery-powered applications with autoplug adaptors. The LT3437’s best in classperformancemeets all of these requirements in a small thermallyenhanced 3mm × 3mm DFN package.
標(biāo)簽： 378 DN 低靜態(tài)電流 單片式
上傳時(shí)間： 2013-10-15
上傳用戶：stampede
Avalanche photo diode (APD) receiver modules arewidely used in fi ber optic communication systems. AnAPD module contains the APD and a signal conditioningamplifi er, but is not completely self contained. It stillrequires signifi cant support circuitry including a highvoltage, low noise power supply and a precision currentmonitor to indicate the signal strength. The challenge issqueezing this support circuitry into applications withlimited board space. The LT®3482 addresses this challengeby integrating a monolithic DC/DC step-up converter andan accurate current monitor. The LT3482 can supportup to a 90V APD bias voltage, and the current monitorprovides better than 10% accuracy over four decades ofdynamic range (250nA to 2.5mA).
上傳時(shí)間： 2014-01-18
上傳用戶：wenyuoo
Photomultipliers (PMT), avalanche photodiodes (APD),ultrasonic transducers, capacitance microphones, radiationdetectors and similar devices require high voltage,low current bias. Additionally, the high voltage must bepristinely free of noise; well under a millivolt is a commonrequirement with a few hundred microvolts sometimesnecessary. Normally, switching regulator confi gurationscannot achieve this performance level without employingspecial techniques. One aid to achieving low noise is thatload currents rarely exceed 5mA. This freedom permitsoutput fi ltering methods that are usually impractical
標(biāo)簽： DCDC 高電壓 低噪音 轉(zhuǎn)換器
上傳時(shí)間： 2013-10-28
上傳用戶：lhw888
基于CC1110單片機(jī)公交報(bào)站系統(tǒng)主要由CC1110單片機(jī)最小系統(tǒng)和WT588D語(yǔ)音模塊組成，提出了如何實(shí)現(xiàn)語(yǔ)音報(bào)站，通過(guò)無(wú)線通信SimpliciTI網(wǎng)絡(luò)協(xié)議實(shí)現(xiàn)公交站臺(tái)的自動(dòng)播報(bào)和OLCD液晶顯示公交運(yùn)行的各類信息。結(jié)果表明，該公交報(bào)站系統(tǒng)報(bào)站準(zhǔn)確率99%，價(jià)格比同類產(chǎn)品下降了300%以上，系統(tǒng)組成結(jié)構(gòu)簡(jiǎn)單，提高了系統(tǒng)的抗干擾性和穩(wěn)定性，也便于攜帶。 Abstract: The bus stop announcement system based on CC1110 MCU is composed of CC1110 MCU minimum system and WT588D voice module. How to achieve the voice announcing is put forward.The bus-stop will announce automatically and display on the OLCD by means of wireless communication SimpliciTI network protocol. As a result， the bus station stop announcement systems reported 99% accuracy rate， price of similar products declined by 300% or more， system of simple structure， improve the anti-jamming and stability of the power system， it is also portable.
標(biāo)簽： 1110 CC 單片機(jī) 公交報(bào)站
上傳時(shí)間： 2013-10-21
上傳用戶：baby25825
The CAT93C46 is a 1 kb Serial EEPROM memory device which isconfigured as either 64 registers of 16 bits (ORG pin at VCC) or 128registers of 8 bits (ORG pin at GND). Each register can be written (orread) serially by using the DI (or DO) pin. The CAT93C46 features aself−timed internal write with auto−clear. On−chip Power−On Resetcircuit protects the internal logic against powering up in the wrongstate.
上傳時(shí)間： 2013-11-20
上傳用戶：ynzfm
Bootloader是微處理器上電時(shí)運(yùn)行的第一段代碼，它可以通過(guò)通信接口實(shí)現(xiàn)對(duì)微處理器內(nèi)部應(yīng)用程序的更新升級(jí)，為網(wǎng)絡(luò)化嵌入式產(chǎn)品的應(yīng)用程序升級(jí)帶來(lái)極大的便利。由于目前沒有統(tǒng)一嵌入式系統(tǒng)的Bootloader。基于NEC 78K0系列單片機(jī)自編程原理，設(shè)計(jì)出一個(gè)適用于78K0/Fx2系列單片機(jī)的Bootloader，并能夠通過(guò)單片機(jī)串口在線升級(jí)應(yīng)用程序。 Abstract: Bootloader is the first piece of code executed after microprocessor startup. It makes the embedded product’s firmware update conveniently through communication interface. However， no unified bootloader is available for all kinds of microprocessor products. Based on the principle of self-programming NEC 78K0s’ series， a useful Bootloader which is suitable for 78K0/Fx2s’ series MCU is designed，the design can update the application through serial ports.
標(biāo)簽： Bootloader MCU 自編程
上傳時(shí)間： 2013-10-26
上傳用戶：fang2010
The CAT28LV64 is a low voltage, low power, CMOS Parallel EEPROM organized as 8K x 8−bits. It requires a simple interface for in−system programming. On−chip address and data latches, self−timed write cycle with auto−clear and VCC power up/down write protection eliminate additional timing and protection hardware. DATA Polling and Toggle status bit signal the start and end of the self−timed write cycle. Additionally, the CAT28LV64 features hardware and software write protection.
上傳時(shí)間： 2013-11-16
上傳用戶：浩子GG
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