毕设翻译英文.docx

1、毕设翻译英文轨道交通学院毕业设计（论文）外文翻译题目： 列车车载的直流恒流源的设计 专 业 电子信息工程 班 级 10115111 学 号 1011511137 姓 名 赵士伟 指 导 教 师 陈文 2014 年 3 月 3 日本文摘自：IEEE TRANSACTIONS ON INDUSTRY AND GENERAL APPLICATIONS VOL. IGA-2, NO.5 SEPT/OCT 1966Highly Regulated DC Power SuppliesAbstract-The design and application of highly regulated dc pow

2、er supplies present many subtle, diverse, and interesting problems. This paper discusses some of these problems (especially inconnection with medium power units) but emphasis has been placed more on circuit economics rather than on ultimate performance.Sophisticated methods and problems encountered

3、in connection with precision reference supplies are therefore excluded. The problems discussed include the subjects of temperature coefficient,short-term drift, thermal drift, transient response degeneration caused by remote sensing, and switching preregualtor-type units and some of their performanc

4、e characteristics.INTRODUCTIONANY SURVEY of the commercial de power supply field will uncover the fact that 0.01 percent regulated power supplies are standard types and can be obtained at relatively low costs. While most users of these power supplies do not require such high regulation, they never-t

5、heless get this at little extra cost for the simple reason that it costs the manufacturer very little to give him 0.01 percent instead of 0.1 percent. The performance of a power supply, however, includes other factors besides line and load regulation. This paper will discuss a few of these-namely, t

6、emperature coefficient, short-term drift, thermal drift, and transient response. Present medium power dc supplies commonly employ preregulation as a means of improving power/volume ratios and costs, but some characteristics of the power supply suffer by this approach. Some of the short-comings as we

7、ll as advantages of this technology will be examined.TEMPERATURE COEFFICIENT A decade ago, most commercial power supplies were made to regulation specifications of 0.25 to 1 percent. The reference elements were gas diodes having temperature coefficients of the order of 0.01 percent 1. Consequently,

8、the TC (temperature coefficient) of the supply was small compared to the regulation specifications and often ignored. Today, the reference element often carries aTC specification greater than the regulation specification.While the latter may be improved considerably at little cost increase, this is

9、not necessarily true of TC. Therefore,the use of very low TC zener diodes, matched differential amplifier stages, and low TC wire wound resistors must be analyzed carefully, if costs are to be kept low.A typical first amplifier stage is shown in Fig. 1. CRI is the reference zener diode and R, is the

10、 output adjustment potentiometer. Fig. 1. Input stage of power supply.Fig. 2. Equivalent circuit of zener reference.Let it be assumed that e3, the output of the stage, feedsadditional differential amplifiers, and under steady-state conditions e3 = 0. A variation of any of the parameters could cause

11、the output to drift; while this is also true of the other stages, the effects are reduced by the gain of all previous stages. Consequently, the effects of other stages will be neglected. The following disculssion covers the effects of all elements having primary and secondary influences on the overa

12、ll TC.Effect of R3 The equivalent circuit of CRI -R3 branch is shown in Fig. 2. The zener has been replaced with its equivalent voltage source E/ and internal impedance R,. For high gain regulators, the input of the differential amplifier will have negligible change with variations of R3 so thatbefo

13、re and after a variation of R3 is made.If it is further assumed that IB Iz; then from (1)Also,Eliminating I, from (2b),andNow, assuming thatthen,Equation (2b) can also be writtenThe Zener Diode The zener diode itself has a temperature coefficient andusually is the component that dominates the overal

14、l TCof the unit. For the circuit of Fig. 1, the TC of the circuit describes, in essence, the portion of the regulator TC contributed by the zener. If the bridge circuit shown in Fig. 1 were used in conjunction with a dropping resistor so that only a portion of the output voltage appeared across the

15、bridge circuit shown, the TC of the unit and the zener would be different. Since the characteristic of zeners is so well known and so well described in the literature, a discussion will not be given here 2.Variation of Base-Emitter VoltagesNot only do the values of V, of the differential am-plifier

16、fail to match, but their differentials with tem perature also fail to match. This should not, however,suggest that matched pairs are required. The true reference voltage of Fig. 1 is not the value E, but E, + (Vie, -Vbe2)-Since, for most practical applicatioinsthe TC of the reference will be the TC

17、of the zener plusConsidering that it is difficult to obtain matched pairs that have differentials as poor as 50 V/C, it becomes rather apparent that, in most cases, a matched pair bought specifically for TC may be overdesigning.Example 2: A standard available low-cost matched pair laims 30AV/C. In c

18、onjunction with a 1N752, the ontribution to the overall TC would beTests, performed by the author on thirteen standard germanium signal transistors in the vicinity of room temperature and at a collector current level of 3 mA,indicated that it is reasonable to expect that 90 to 95 percent of the unit

19、s would have a base-emitter voltage variation of -2.1 to -2.4 mV/C. Spreads of this magnitude have also been verified by others (e.g., Steiger3). The worst matching of transistors led to less than 400 ,V/C differential. In conjunction with a 1N752,even this would give a TC of better than 0.007%/0C.V

20、ariation of Base CurrentsThe base current of the transistors is given by A variation of this current causes a variation in signal voltage at the input to the differential amplifier due to finite source impedances. Matching source impedances is not particularly desirable, since it reduces the gain of

21、 the system and requires that transistors matched for I,o and A be used. Hunter 4 states that the TC of a is in the range of +0.2%/0C to -0.2%7/C and that 1, may be approximated by where Ao is the value at To. is also temperature dependent and Steiger 3 experimentally determined the variation to be

22、from about 0.5%/C to 0.9%/0C.And，Fig. 3. Input circuit of Q2.The current AIB flows through the source impedance per Fig. 3. The drops in the resistance string, however, are subject to the constraint that EB (and AEB) are determined by the zener voltage and the base-emitter drops of Q1 and Q2. Conseq

23、uently, if in going from temperature T1to T2 a change AEB occurs,The change in output voltage isAndExample 3: For Q2 (at 25C)(see Example 1)Variation of R,The effects of a variation of the TC between RIA and RIB is sufficiently self-evident so that a discussion of the contribution is not included.SH

24、ORT-TERM DRIFTThe short-term drift of a supply is defined by the National Electrical Manufacturers Association (NEMA) as a change in output over a period of time, which change is unrelated to input, environment, or load 5.Much of the material described in the section on temperature coefficient is ap

25、plicable here as well. It has been determined experimentally, however, that thermal air drafts in and near the vicinity of the power supply contributes enormously to the short-term characteristics. The cooling effects of moving air are quite well known, but it is not often recognized that even extre

26、mely slow air movements over such devices as zeners and transistors cause the junction temperature of these devices to change rapidly. If the TC of the supply is large compared to the regulation, then large variations in the output will be observed. Units having low TCs achieved by compensation-that

27、 is, by canceling out the effects of some omponents by equal and opposite effects of others may still be plagued by these drafts due to the difference in thermal time constants of the elements.Oftentimes, a matched transistor differential amplifier in a common envelope is used for the first amplifie

28、r just to equalize and eliminate the difference in cooling effects between the junctions. Approximations to this method include cementing or holding the transistors together, imbedding the transistors in a common metal block, etc. Excellent results were achieved by the author by placing the input st

29、age and zener reference in a separate enclosure. This construction is shown in Fig. 4. The improvement in drift obtained by means of the addition of the metal cover is demonstrated dramatically in Fig. 5.Fig. 5. Short-term drift of a power supply similar to the one shown in Fig. 4 with and without p

30、rotective covers. The unit was operated without the cover until time tl, when the cover was attached. The initial voltage change following t, is due to a temperature rise inside the box.Fig. 5. Short-term drift of a power supply similar to the one shown n Fig. 4 with and without protective covers. T

31、he unit was operated without the cover until time tl, when the cover was attached. The initial voltage change following t, is due to a temperature rise inside the box.If potentiometers are used in the supply for output adjustment (e.g., RI), care should be used in choosing the value and design. Vari

32、ations of the contact resistance can cause drift. It is not always necessary, however, to resort to the expense of high-resolution multiturn precision units to obtain low drift. A reduction in range of adjustment, use of low-resistance alloys and low-resolution units which permit the contact arm to rest firmly between turns, may be just as satisfactory. Of course, other considerations should include the ability of both the arms and the wire to resist corrosion. Sil