It has been said that the move from narrowband to broadband access is the second revolution for the Internet — ‘broadband is more bandwidth than you can use’. Once users have experienced broadband access there is no turning back. A whole new world of applications and services becomes possible. No longer is it the ‘world- wide wait’. The speed of response and visual quality enabled by broadband finally allows the Internet to reach its true potential.
上传时间： 2020-06-06
上传用户：shancjb
December 2007, San Jose, California: It seems a long time ago. I walked into a big networking company to head their small Power over Ethernet (PoE) applications team. Surprisingly, I hardly knew anything about PoE prior to that day, having been a switching-power conversion engineer almost all my life. But it seemed a great opportunity to widen my horizons. As you can see, one notable outcome of that seemingly illogical career choice five years ago is the book you hold in your hands today. I hope this small body of work goes on to prove worthy of your expectations and also of all the effort that went into it. Because, behind the scenes, there is a rather interesting story to relate—about its backdrop, intertwined with a small slice of modern PoE history, punctuated by a rather res- tive search for our roots and our true heroes, one that takes us back almost two centuries
上传时间： 2020-06-07
上传用户：shancjb
RFID (radio-frequency identification) is the use of a wireless non-contact system that uses radio-frequencyelectromagnetic fields to transfer datafrom a tag attached to an object, for the purposes of automatic identification and tracking [38]. The basic technologies for RFID have been around for a long time. Its root can be traced back to an espionage device designed in 1945 by Leon Theremin of the Soviet Union,whichretransmittedincidentradiowaves modulatedwith audioinformation. After decades of development, RFID systems have gain more and more attention from both the research community and the industry.
标签： Infrastructure RFID as an
上传时间： 2020-06-08
上传用户：shancjb
We are in the era of ubiquitous computing in which the use and development of Radio Frequency Iden- tification (RFID) is becoming more widespread. RFID systems have three main components: readers, tags, and database. An RFID tag is composed of a small microchip, limited logical functionality, and an antenna. Most common tags are passive and harvest energy from a nearby RFID reader. This energy is used both to energize the chip and send the answer back to the reader request. The tag provides a unique identifier (or an anonymized version of that), which allows the unequivocal identification of the tag holder (i.e. person, animal, or items).
上传时间： 2020-06-08
上传用户：shancjb
I can remember buying my first electronic calculator. I was teaching a graduate level statistics course and I had to have a calculator with a square root function. Back in the late 1960s, that was a pretty high-end requirement for a calculator. I managed to purchase one at the “educational discount price” of $149.95! Now, I look down at my desk at an ATmega2560 that is half the size for less than a quarter of the cost and think of all the possibilities built into that piece of hardware. I am amazed by what has happened to everything from toasters to car engines. Who-da-thunk-it 40 years ago?
上传时间： 2020-06-09
上传用户：shancjb
Inventors have long dreamed of creating machines that think. This desire dates back to at least the time of ancient Greece. The mythical figures Pygmalion, Daedalus, and Hephaestus may all be interpreted as legendary inventors, and Galatea, Talos, and Pandora may all be regarded as artificial life ( , Ovid and Martin 2004 Sparkes 1996 Tandy 1997 ; , ; , ).
上传时间： 2020-06-10
上传用户：shancjb
本设计介绍了一种基于STM32单片机控制的智能水杯,可利用插口式电源或无线充电底座为加热器提供能量,并在达到某种饮品所需温度时进行保温。水杯内置充电电池,可选用USB接口或无线充电。在水杯内部设置无线模块,用户利用手机App与水杯进行匹配进行加热操作,加热完后水杯会通过手机App和液晶显示屏实时反馈液体温度,通过指示灯显示电量情况等,给用户进行提醒。该智能水杯设计创新,实用价值较高。This paper introduces an intelligent water cup based by STM32 microcontroller,it can provide energy for the heater by socket type power supply or wireless charging base,and hold temperature needed for some kind of drink.Builtedin rechargeable battery,water cup can use USB or wireless charging.The wireless module is set up inside it,and customers can use mobile App to match and heat.After heating,water cup feeds back liquid temperature through the mobile App,and then displays on LCD,reminds users through the indicator light.The intelligent water cup is designed innovatively and has high practical value.
上传时间： 2022-03-28
上传用户：
主要內容介紹 Allegro 如何載入 Netlist，進而認識新式轉法和舊式轉法有何不同及優缺點的分析，透過本章學習可以對 Allegro 和 Capture 之間的互動關係，同時也能體驗出 Allegro 和 Capture 同步變更屬性等強大功能。Netlist 是連接線路圖和 Allegro Layout 圖檔的橋樑。在這裏所介紹的 Netlist 資料的轉入動作只是針對由 Capture（線路圖部分）產生的 Netlist 轉入 Allegro（Layout部分）1． 在 OrCAD Capture 中設計好線路圖。2． 然後由 OrCAD Capture 產生 Netlist（annotate 是在進行線路圖根據第五步產生的資料進行編改）。 3． 把產生的 Netlist 轉入 Allegro（layout 工作系統）。 4． 在 Allegro 中進行 PCB 的 layout。 5． 把在 Allegro 中產生的 back annotate（Logic）轉出（在實際 layout 時可能對原有的 Netlist 有改動過），並轉入 OrCAD Capture 裏進行回編。
上传时间： 2022-04-28
上传用户：kingwide
基于TMS320F28035芯片为控制核心的空间矢量异步电机变频器 我们设计的异步电机变频调速器以TMS320F28035芯片为控制核心，通过输出三相PWM波控制智能功率模块IPM驱动三相异步电机。我们使用空间矢量SVPWM算法，并对其进行了优化。采用检测反电势的方法省去了昂贵的光电编码器，大大节省了成本。同时开创性的研发了自动根据运行环境调节的自适应变频算法，使我们的变频调速器可以在电网条件恶劣的乡村山区工作，由此该变频器已被一家民用水泵生产企业预订。关键字 变频器 TMS320f28035 IPM SVPWM In our design, the asynchronous machine inverter based on the chip of TMS320F28035 drives the three-Phase asynchronous machine by sending three-phase PWM waves to the IPM, which is short for the Intelligent-Power-Module. The SVPWM (space vector pulse width modulation) strategy is applied to our control algorithm and we optimize it mainly in two aspects. Firstly the inverter detects the speed by measuring the Back EMF instead of installing an expensive photoelectric encoder for costs reduction.
标签： tms320f28035 芯片
上传时间： 2022-05-08
上传用户：zhanglei193
PFC基础知识-PF的定义1功率因数（Power Factor）的定义是指输入有功功率（p）和视在功率（S）的比值；线性电路功率因数可用Cos表示，为正弦电流与正弦电压的相位差；但是由于整流电路中二极管的非线性，导致输入电流为严重的非正弦波形，用cosp已不能表示整流电路的功率因数；常规直接整流电路的滤波电容使输出电压平滑，但却使输入电流变为尖脉冲，并产生高次谐波分量。输入电流波形变，导致功率因数下降，污染电网，甚至造成电子设备损坏。引入功率因数校正是必要的利用功率因数校正技术可A/全跟踪交流输入电压波形，流输入电流波形完使输入电流波形皇纯正弦波，并且与输入电压波形相位，，此时整流器的货载可等效为纯电阻。根据常用功率因数校正方法可分为有源功率因数校正（APFC）技术与无源功率因数校正（PPFC）技术。它置于桥式整流器与滤波用电解电容器之间，实际上是一种DC-DC变换器。无源功率因数校正是利用电感和电容组成滤波器，对输入电容进行移相和整形。有源功率因数校正（APFC：Active Power Factor Correction），在负载即电力电子装置本身的整流器和滤波电容之间增加一个功率变换电路，将整流器的输入电流校正成为与电网电压同相位的正弦波，消除了谐波和无功电流，因而将电网功率因数提高到近似为1.APFC电路常用拓扑：升压式（Boost）降压式（Buck）升/降压式（Buck/Boost）反激式（Fly back）APFC电路形式：单极式 双极式单相PFC 三相PFCBoost变换电路是有源功率因数校正器主回路拓扑的极好选择。优点：输入电流连续，因而产生低的传导噪声和最好的输入电流波形；缺点：需要比输入峰值电压还要高的输出电压。
标签： pfc
上传时间： 2022-05-28
上传用户：
