Power-Supplies

1、1電源電源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 curre

2、nt (DC) voltages for equipment operation. 電氣的電氣的電子的電子的設備設備電壓電壓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.電路電路be considered as1. 被看作 2. 被認為是 裝置、設備裝置、設備轉(zhuǎn)換轉(zhuǎn)換6 The AC voltage from the power lines can

3、 be rectified directly or passed through an isolation transformer ( a turns ratio of 1:1). Rectify rektifai改正，校正;電整流隔離變壓器78 Depending on the value of DC voltage needed, the transformer may be of either a step-up or step-down type. 根據(jù)根據(jù)升壓升壓降壓降壓9 After the transformer, the AC is rectified into pulsati

4、ng DC by diodes in the form of a half-wave rectifier, a full-wave rectifier, or a bridge (full-wave) rectifier. plseitvi.搏動;悸動;有規(guī)律地跳動 二極管二極管10half-wave rectifierfull-wave rectifierbridge (full-wave) rectifier11 The pulsating DC is then filtered or smoothed out by capacitors, inductors, and resistors

5、 so as to produce a constant DC output. 濾波濾波smooth out弄平;緩和，調(diào)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 conduct

6、s. anode，陽極，正極，陽極，正極cathode ，陰極，負極，陰極，負極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 dio

7、de 4 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 di

8、odes ( two diodes are conducting at a time): FpeakoUUU2 最高的最高的;最大值的最大值的18輸出電壓平均值：輸出電壓平均值：UL=0.9u2輸出電流平均值輸出電流平均值:IL= UL/RL =0.9 u2 / RL 流過二極管的平均電流：流過二極管的平均電流：ID=IL/2u2ttuL主要參數(shù)：主要參數(shù)：二極管承受的最大反向電壓：二極管承受的最大反向電壓：URM=22u+41232+43DuuDDL21LDR-19 Full-wave bridge rectifier modules containing four diodes in a

9、single unit are commercially available. 商業(yè)上的模塊;組件 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 電容濾波電路電容濾波電路工作原理工作原理濾波電容濾波電容D1D2D3D4RLTuiu2uOCu2tuot無濾波電容無濾波電容時的波形時的波形加入濾波電容加入濾波電容時的波形時

10、的波形22 u2上升，上升， u2大于電容大于電容上的電壓上的電壓uc，u2對電容充對電容充電，電，uo= uc u2 u2下降，下降， u2小于電容上小于電容上的電壓。二極管承受反向的電壓。二極管承受反向電壓而截止。電容電壓而截止。電容C通過通過RL放電，放電， uc按指數(shù)規(guī)律下降，按指數(shù)規(guī)律下降，時間常數(shù)時間常數(shù) = 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

11、 flow 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 superi

12、mposed 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

13、 voltage (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

14、) and 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

15、 When 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

16、sometimes 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. 37

17、38 When 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

18、, meaning 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 th

19、e same circuit, if necessary. 41 1. Put the Phrases into English 2. Put the Phrases into Chinese 42 1）穩(wěn)壓電源 2）橋式整流器 3）脈沖直流電 4）二極管的正極 5）峰值電壓1) electronic power supply 或 steady DC Voltage source2) bridge rectifier3) pulsating DC 4) anode of diode5) peak voltage單擊鼠標顯示答案43 6）電容濾波器 7）充電和放電 8）穩(wěn)壓管 9）電氣電子工程師

20、學會 10）專業(yè)技術組織6) capacitor filter7) charge and discharge8) zener diode9) IEEE (Institute of Electrical and Electronics Engineers)10) technical professional association單擊鼠標顯示答案441) equipment operation2) device that converts AC into DC3) the power lines4) depending on the value of DC voltage needed5) a half-wave rectifier1) 設備的運行2) 把交流電轉(zhuǎn)換成直流電的器件（設備）3) 電源線4) 根據(jù)（取決于）所需要的直流電壓值5) 半波整流器單擊鼠標顯示答案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)