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
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