Power-Supplies.ppt

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1、2 Read the following passage, paying attention to the question. 1) What is the function of an electronic power supply? 2) What does an electronic power supply include ?3 There are many types of electrical and electronic power supplies, providing various alternating current (AC) and direct current (D

2、C) voltages for equipment operation. 电气的电气的电子的电子的设备设备电压电压45 DC voltages are needed for most electronic circuits, and generally an electronic power supply is considered as a device that converts AC into DC.电路电路be considered as1. 被看作 2. 被认为是 装置、设备装置、设备转换转换6 The AC voltage from the power lines can be r

3、ectified directly or passed through an isolation transformer ( a turns ratio of 1:1). Rectify rektifai改正，校正;电整流隔离变压器78 Depending on the value of DC voltage needed, the transformer may be of either a step-up or step-down type. 根据根据升压升压降压降压9 After the transformer, the AC is rectified into pulsating DC

4、 by diodes in the form of a half-wave rectifier, a full-wave rectifier, or a bridge (full-wave) rectifier. plseitvi.搏动;悸动;有规律地跳动 二极管二极管10half-wave rectifierfull-wave rectifierbridge (full-wave) rectifier11 The pulsating DC is then filtered or smoothed out by capacitors, inductors, and resistors so a

5、s to produce a constant DC output. 滤波滤波smooth out弄平;缓和，调解12 The bridge rectifier produces a full-wave DC output with the use of four diodes (Fig 5.1). 13 When the positive half-cycle appears, the anode of diode 1 is positive and it conducts, and the cathode of diode 2 is negative and it conducts. an

6、ode，阳极，正极，阳极，正极cathode ，阴极，负极，阴极，负极14 Current flows from the AC source through diode 1, through RL, through diode 2, and back to the source. Diodes 3 and 4 are reversed biased and no current flows through them. They appear as open circuits. 反向偏置反向偏置15 On the negative half-cycle the anode of diode 4

7、is positive and it conducts, and the cathode of diode 3 is negative and it conducts. 16 Current flows from the AC source through diode 4, through RL, through diode 3, and back to the source. Diodes 1 and 2 are reverse. 17 Voltage output Uo is the peak voltage less two times the UF across the diodes

8、( two diodes are conducting at a time): FpeakoUUU2 最高的最高的;最大值的最大值的18输出电压平均值：输出电压平均值：UL=0.9u2输出电流平均值输出电流平均值:IL= UL/RL =0.9 u2 / RL 流过二极管的平均电流：流过二极管的平均电流：ID=IL/2u2ttuL主要参数：主要参数：二极管承受的最大反向电压：二极管承受的最大反向电压：URM=22u+41232+43DuuDDL21LDR-19 Full-wave bridge rectifier modules containing four diodes in a singl

9、e unit are commercially available. 商业上的模块;组件 20 Capacitors are used in power supplies to smooth out pulsating DC and to produce steady DC voltage. A simple capacitor filter is connected across the output. 21 电容滤波电路电容滤波电路工作原理工作原理滤波电容滤波电容D1D2D3D4RLTuiu2uOCu2tuot无滤波电容无滤波电容时的波形时的波形加入滤波电容加入滤波电容时的波形时的波形22

10、 u2上升，上升， u2大于电容大于电容上的电压上的电压uc，u2对电容充对电容充电，电，uo= uc u2 u2下降，下降， u2小于电容上小于电容上的电压。二极管承受反向的电压。二极管承受反向电压而截止。电容电压而截止。电容C通过通过RL放电，放电， uc按指数规律下降，按指数规律下降，时间常数时间常数 = RL Cuot工作原理工作原理23 When this peak voltage begins to decrease, the stored electrons in the negative side of the capacitor will discharge and flow

11、 through the load in an attempt to keep the voltage constant across the capacitor. 24 Another pulsating DC comes soon after the discharge and charges the capacitor to peak voltage again. The slight charging and discharging of the capacitor produces a ripple voltage (AC component) that is superimpose

12、d on the top of the steady DC (Fig 5.2). 25 A zener diode is a specially doped diode that operates the same as a regular diode in the forward-biased condition (it allows large current to flow). 26 However, in the reverse-biased condition (Fig 5.3), it will not conduct until it reaches the zener volt

13、age (Uz) at which it is designed. 27 At this point the zener diode conducts current in the reverse direction, while maintaining the zener voltage across its terminals (Fig 5.4). 28 The amount of current that flows through it is determined by two factors, a series (current-limiting) resistor (RS) and

14、 the parallel load resistance (RL). 293031 Resistor RS is found by the formula where . With no load, a specific amount of current (Iz=IRs) flows through the zener diode and RS. zRSsIURzsourceRSUUU32 Voltage drop URs plus Uz will equal Usource (Usource should be at least 1 V greater than Uz). 33 When

15、 a load is connected across the zener diode, the diode current decreases by the amount drawn by the load so that the current through RS remains constant (Iz=IRs - IRL). 34 The zener diode maintains the voltage across its terminals by varying the current that flows through it. 35 The 78xx (also somet

16、imes known as LM78xx) series of devices is a family of self-contained fixed linear voltage regulator integrated circuits（Fig 5.5）. 36 The 78xx family is a very popular choice for many electronic circuits which require a regulated power supply, due to their ease of use and relative cheapness. 3738 Wh

17、en specifying individual ICs within this family, the xx is replaced with a two-digit number, which indicates the output voltage the particular device is designed to provide (for example, the 7805 has a 5 volt output, while the 7812 produces 12 volts). 39 The 78xx are positive voltage regulators, mea

18、ning that they are designed to produce a voltage that is positive relative to a common ground. 40 There is a related line of 79xx devices which are complementary negative voltage regulators. 78xx and 79xx ICs can be used in combination to provide both positive and negative supply voltages in the sam

19、e circuit, if necessary. 41 1. Put the Phrases into English 2. Put the Phrases into Chinese 42 1）稳压电源 2）桥式整流器 3）脉冲直流电 4）二极管的正极 5）峰值电压1) electronic power supply 或 steady DC Voltage source2) bridge rectifier3) pulsating DC 4) anode of diode5) peak voltage单击鼠标显示答案43 6）电容滤波器 7）充电和放电 8）稳压管 9）电气电子工程师学会 10

20、）专业技术组织6) capacitor filter7) charge and discharge8) zener diode9) IEEE (Institute of Electrical and Electronics Engineers)10) technical professional association单击鼠标显示答案441) equipment operation2) device that converts AC into DC3) the power lines4) depending on the value of DC voltage needed5) a half-

21、wave rectifier1) 设备的运行2) 把交流电转换成直流电的器件（设备）3) 电源线4) 根据（取决于）所需要的直流电压值5) 半波整流器单击鼠标显示答案45 6) so as to produce a constant DC output 7) in the negative side of the capacitor 8) flow through the load 9) in the forward-biased condition 10) a series ( current-limiting) resistor6) 从而产生一个稳定的直流输出7) 在电容的负极8) 流过负

22、载9) 在加正向偏置（电压）的条件下10) 一个串联（限制电流）电阻单击鼠标显示答案461) However, in the reverse-biased condition, it will not conduct until it reaches the zener voltage (Uz).1) 然而在反向偏置时，除非外加电压达到稳压电压(Uz)（设计时确定的），否则它不导通。单击鼠标显示答案472) After the transformer, the AC is rectified into pulsating DC by diodes in the form of a bridge

23、 rectifier. 2) 从变压器副边流出的交流电流通过二极管构成的桥式整流器整流成为脉冲直流电。单击鼠标显示答案483) Before the capacitor discharges too far, another DC pulse arrives to recharge the capacitor back to the peak voltage. 电容放电不久，另一个直流脉冲又到了，再次对电容充电使它达到峰值电压。单击鼠标显示答案498) You generally talk about household electrical service as single-phase, 220-volt AC service. 8) 通常提到的民用电就是单相，220V交流电源。单击鼠标显示答案