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1、高精度稳压直流电源文摘:目前对于可调式直流电源的设计和应用现在有很多微妙的,多种多样的,有趣的问题。探讨这些问题(特别是和中发电机组有关),重点是在电路的经济适用性上,而不是要达到最好的性能。当然，对那些精密程度要求很高的除外。讨论的问题包括温度系数，短期漂移，热漂移，瞬态响应变性遥感和开关preregualtor型机组及和它的性能特点有关的的一些科目。介绍 从商业的角度来看供电领域可以得到这样一个事实，在相对较低的成本下就可以可以获得标准类型的0.01%供电调节。大部分的供电用户并不需要这么高的规格，但是供应商不会为了减少客户这么一点的费用而把0.1%改成0.01%。并且电力供应的性能还包括
2、其他一些因素，比如说线路和负载调解率。本文将讨论关于温度系数、短期漂移、热漂移,和瞬态的一些内容。 目前中等功率直流电源通常采用预稳压来提高功率/体积比和成本，但是只有某些电力供应采用这样的做法。这种技术的优缺点还有待观察。温度系数十年以前，大多数的商业电力供应为规定的0.25%到1%。这里将气体二极管的温度系数定位百分之0.011。因此，人们往往会忽视TC（温度系数）是比规定的要小的。现在参考的TC往往比规定的要大的多。为了费用的减少，后者会有很大的提高，但是这并不是真正的TC。因此，如果成本要保持在一个低的水平，可以采用TC非常低的齐纳二极管，安装上差动放大电路，还要仔细的分析低TC绕线电
3、阻器。如图1所示，一个典型的放大器的第一阶段，其中CR1是参考齐纳二极管，R是输出电位调节器。图1 电源输入级 图2 等效的齐纳参考电路假设该阶段的输出是e3，提供额外的差分放大器，在稳定状态下e3为零，任何参数的变化都会引起输出的漂移；对于其他阶段来说也是一样的，其影响是减少了以前所有阶段的增益。因此，其他阶段的影响将被忽略。以下讨论的内容涵盖了对于TC整体的无论是主要的还是次要的影响。R3的影响 CR1-R3分支的等效的电路如图2所示，将齐纳替换成了它的等效电压源E和内部阻抗R2。对于高增益调节器，其中R3的变化对差分放大器的输入来说可以忽略不计，所以前后的变化由R3决定。如果进一步假定I
4、B Iz;从（1）可以得到同时，消除Iz，由（2b）可得并且现在，假设那么，方程式（2b）也可以写成例1：齐纳二极管齐纳二极管拥有自己的温度系数，通常，它在TC的整体中占有很重要的位置。对于电路图1，TC电路的介绍，从本质上讲，稳压器的TC部分由齐纳贡献。如果桥接如电路图1显示.被用于并联一个下降电阻,只有部分输出电压出现过了桥显示电流,TC的单位和齐纳会有所不同。由于齐纳二极管的特点是众所周知的，各文献对于它的描述非常好，这里将不予讨论2。基级与放射级电压的变化 不只是差分放大器Vbe的值不匹配，温度的差距也不匹配。不应该这样，无论怎样，互相协调是有必要的。图1真实的参考电压不是E1而是E2
5、+(Vbe1-Vbe2)。 因为，对于大多数的实际应用TC的参考价值将比齐纳的TC优先考虑到很难获得高达50 V/C的差，这就会变得相当明显，在大多数情况下,TC可能会超出额定值。例2:一个30AV/C下安全的，低成本的设计。与一个1N752并联，整体的TC将会是 实验，笔者计算出在室温情况下13个标准的锗晶体管的信号，集电极的电流水平为3mA，说明了它的合理值是90%到95%，基极和集电极之间将有一个-2.1至-2.4毫伏的变化。人们已经验证出了如此庞大的利差（例如，施泰格3）。最糟糕的情况是电晶体导致不到400V /C微分。与一个1N752并联甚至可能会给出一个0.007%/C更好的TC。
6、基极电流的变化 该基级晶体管的电流由下式给出由于有限源阻抗变化，一个电流变化造成了差分放大器的信号电压输入的变化。所用的电源的阻抗不是特别的理想，因为对于所使用的晶体管的I和来说它减少了系统的增益和需求。亨特4指出的值域范围是在+0.2/至-0.2之间，还有I可能近似于其中A0的值由T0决定。还取决于温度，施泰格3还通过实验证明了它的变化范围是在0.5/ C到0.9/ C之间。并且图3 Q2的输入电路当前情况下IB流经图3上的每一个电源阻抗，在电阻串中变小，是由齐纳电压值和基极与发射极之间Q1和Q2之间的落差所造成的EB (and EB)所束缚着。因此，如果要看温度从T1变到T2时EB的变化输
7、出电压的变化并且，例3:假设有Q3(在25摄氏度)（同例1）R1的变化R1A和R1B的TC的变化的影响是很明显的，这里不做讨论。短期漂移短期漂移是由国家电气制造商协会（NEMA）提供，可以这样说“这段时间的输出与输入，环境和负载无关”5。在上一节中对温度系数的描述在这里也适用。据试验测定，在电源里面和它附近的热空气极大地提高了短期特性。流动空气的冷却效果是众所周知的，然而人们通常不会意识到就算空气在齐纳二极管和晶体管中移动的很缓慢，它对温度的影响也是很显著地。如果提供比较大的TC，那么输出会有很大的变化。会有低TC实现补偿，也就是说，如果消除了了一些元器件相同或相反的影响，这些元器件的热时间常
8、数仍会受到干扰。一个常用的方法是使用第一个放大器来消除和平衡掉交界处冷却效果上的差异。可以通过晶体管的固定或保持来近似模拟这个方案，将晶体管嵌入在一个共同的金属块中，等等。笔者通过把输入级和参考齐纳放置到一个单独的机箱中取得了很好的效果。如图4所示。在图5中通过金属的覆盖，漂移得到了很好的改善。图4 12V的电源晶体管具有百分之0.01的调节精度。注意，保护盒是用来给第一放大器和参考组件进行隔热保护。图5 和图4类似，电源提供了短期漂移，并且没有保护措施。该元件是没有覆盖的，直到t1。盒子里面的温度上升，电压随着时间 t1而变化。如果电位器用于输出地调节（例如R1），应该谨慎的选择价位和设计。
9、接触电阻的变化可引起漂移。用有高精密线圈的元件来获得低漂移是没有必要的。用低电阻的合金和低分辨率的元件可以轮流休息，来缩小范围可以达到同样令人满意的效果。当然，还要考虑到线路的抗腐蚀性等问题。有机硅润滑脂可以得到很好的效果。接触臂的周期的运用对元件的腐蚀有很好的“疗效”。热漂移符合NEMA定义的热漂移就是“由于不正常的环境的变化引起有关的内部环境温度的变化而照成在一定时间内输出的变化。温漂通常与线路电压和负载有关”5。温漂与TC的供应以及整体散热的设计有关。通过对关键部件妥善安置是有可能大大减少甚至完全消除影响。百分之0.01（规定）的耗材有满负载的百分之0.05到0.15之间的漂移，这非常的
10、罕见。事实上，一个制造商曾经说过百分之0.15会更好。减少热漂移除了提高TC以外还可以通过减少内部的消耗来解决。比如说在关键的放大器和散热元件之间放置热障。外表面最好位于通风良好处。应该注意到，只能在百分之0.01和0.05之间索取。瞬态响应大多数该类型的电源有一个还很受争议的负载端电容器。这是出于稳定的目的，通常会决定主要的电源时间常数。这个电容器会导致在遥感模式下短暂的电力供应不良的现象。通常情况下，晶体管电源会在很短的时间内作出反应，但是笔者曾经指出6，在遥感时，反应会变得很小。其等效电源如图6所示。引线从电源到负载电阻R处引入，设备的感应电流Is是相对稳定的。在平衡条件下，图7表明，一
11、个突然的负荷变化会导致Ldi/dt的瞬间激增，我们称之为“尖峰”；以及线性放电时间越长时电容充放电的情况。放电时间是，其中并且，对于Is来说，通常它不会在放大器的最后阶段提供驱动，但是会出现限流现象。遥感是指电源电压电感的直接负荷。图6 远程输出传感的等效电路图7 瞬态响应，遥感。图8 框图。使用预稳压电源可以减少监测和控制的A型阶段电压的使用和损耗。由于主要的调节器往往比预调节器响应更快，应该建立足够的储备来使这个阶段下降。如果不这样可能会导致负载的饱和，那是前置稳压器在响应时间内产生的。开关前置稳压器型机组 传统类- A型晶体管电源供应变得相当笨重，昂贵，与传递阶段拥挤，作为供给增加电流和
12、功率的水平。要求输出调节范围更大,再加上电力的供应是远程可编程的,会极大地提高条件的要求。正是由于这些原因,高效利用的开关调节器作为一种压力调节阀在商业和军事用品应用了许多年。绝大多数的供应整流器可控硅使用与控制元件。从60-cycle操作的系统压力调节阀响应来源,在20至50ms之间。最近对高压、大功率开关晶体管的开关晶体管的方法更具有吸引力。该系统提供了一种低成本,发行量较小的方法,再加上一个submillisecond响应时间。通常是独立的电源频率导致了高开关率。开关频率就可能被固定的,一个被控制的变量或一个独立的自生自储（LC滤波器电路）参数7,8。更快的反应时间是非常可取的,因为它减
13、少了在预备役电压值必须通过阶段或仓库(的数量)的电力需求在压力调节阀过滤器。一个晶体管作为电源开关操作适合具有大电流，高电压等级低漏电流耦合。不幸的是，这些特点是实现了热容量牺牲，同时使电压和电流的条件导致很高的峰值功率可能是灾难性的。因此，它成为强制性的设计负荷高峰期间有足够的条件，也包含开关驱动电流限制或快速过载保护系统。商业发展电力供应总是有输出电流限制,但这并不限制压力调节阀电流负载条件下,除了在稳态(包括短路)。考虑一下,例如,一个电源工作在短路、短被删除突然叫起来。指图8、9月的产量将会快速上涨,减少通过阶段电压,关闭开关晶体管。由此产生的瞬态传达很多周期的交换率),这样电感的压力
14、调节阀过滤变得完全不够的限制流量。因此,当前将会上升直至稳态已恢复、电路电阻引起限制,或不足开车使开关出来的饱和度。上述第二种情况导致开关失败。其他营业状况会产生相似的瞬变包括输出电压编程和初始刺激的用度。输入功率瞬间的中断也应首先要考虑的事。一个解决这个问题的办法就是限制的电压变化的速率在可出现一值,通过舞台了压力调节阀可以遵循。这能被做方便加上足够的输出电容。这电容会同限流特性会产生一种最大的改变的比率其中C0 = output capacity.假设这个压力调节阀遵循这种变化和有滤波电容器冠军杯,然后开关电流在电源在上,压力调节阀的参考电压上升也必须是有限的。采取这一考虑,其中ER =
15、passing stage voltageTl = time constant of reference supply.策略合作关系SCR的使用来代替电晶体的将是一个明显改善由于较高的增兵电流的收视率,却转身他们去了,需要大量的能源。而门策略合作关系SCR讨厌似乎将为员工提供良好的折衷,全部的问题,严峻的限制,在当前的收视率现限制使用它们。参考文献1 j.G.Truxal，控制工程师手册。纽约：McGraw Hill出版社，1958年，11到19页。2摩托罗拉齐纳二极管/整流器手册，第二版。 1961。3瓦特施泰格，“一个晶体管的温度分析及其应用差分放大器，“爱尔兰跨。在仪器仪表，第一卷。 1
16、-8，页82-9，1959年12月。4唱片猎人，半导体电子手册。纽约：McGraw Hill出版社，1956年，第13-3。5“标准出版物的监管电子直流电源，“（未发表稿）电子电源集团，半导体电源转换器部分，NEMA等。6Muchnick，“远程传感晶体管电源”电子产品，1962年9月。7路劳克斯，“在开关型稳压器的设计考虑”固态设计，1963年4月。8四汉考克和B Kurger，“高效率稳压电源采用高速交换”在AIEE冬季干事提交会议，纽约，纽约，1月27号至2月1日，1963年。9河四米德尔，差分放大器。纽约：Wiley，1963。10索伦森控制功率目录和手册。索伦森，雷神公司，南诺沃克，
17、美国康涅狄格州单位。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 power supplies present many subtle, diverse, and interesting problems. This paper discusses some of these p
18、roblems (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 in connection with precision reference supplies are therefore excluded. The problems discussed include t
19、he 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 performance characteristics.INTRODUCTIONANY SURVEY of the commercial de power supply field will uncover the fact t
20、hat 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-theless get this at little extra cost for the simple reason that it costs the manufacturer very little to
21、 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, temperature coefficient, short-term drift, thermal drift, and transient response. Present medium power dc
22、 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 well as advantages of this technology will be examined.TEMPERATURE COEFFICIENT A decade ago, most commerci
23、al 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, the TC (temperature coefficient) of the supply was small compared to the regulation specifications and o
24、ften 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 not necessarily true of TC. Therefore,the use of very low TC zener diodes, matched differential amplifie
25、r 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 output adjustment potentiometer. Fig. 1. Input stage of power supply.Fig. 2. Equivalent circuit of zene
26、r 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 the output to drift; while this is also true of the other stages, the effects are reduced by the gain of
27、 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 overall TC.Effect of R3 The equivalent circuit of CRI -R3 branch is shown in Fig. 2. The zener has been repla
28、ced 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 thatbefore and after a variation of R3 is made.If it is further assumed that IB Iz; then from (1)Also,Eliminatin
29、g 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 overall TCof the unit. For the circuit of Fig. 1, the TC of the circuit describes, in essence, the portion of
30、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 bridge circuit shown, the TC of the unit and the zener would be different. Since the characteristic of z
31、eners 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 fail to match, but their differentials with tem perature also fail to match. This should not, however,su
32、ggest 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 of the zener plusConsidering that it is difficult to obtain matched pairs that have differentials as poo
33、r 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 conjunction with a 1N752, the ontribution to the overall TC would beTests, performed by the author on thi
34、rteen 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 units would have a base-emitter voltage variation of -2.1 to -2.4 mV/C. Spreads of this magnitude have also
35、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.Variation of Base CurrentsThe base current of the transistors is given by A variation of this current cau
36、ses 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 the system and requires that transistors matched for I,o and A be used. Hunter 4 states that the TC of
37、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 from about 0.5%/C to 0.9%/0C.And，Fig. 3. Input circuit of Q2.The current AIB flows through the source im
38、pedance 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. Consequently, if in going from temperature T1to T2 a change AEB occurs,The change in output voltage isAndExamp
39、le 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.SHORT-TERM DRIFTThe short-term drift of a supply is defined by the National Electrical Manufacturers Assoc
40、iation (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 applicable here as well. It has been determined experimentally, however, that thermal air drafts in and ne
41、ar 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 extremely slow air movements over such devices as zeners and transistors cause the junction temperature of th
42、ese 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 is, by canceling out the effects of some omponents by equal and opposite effects of others may still be
43、 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 amplifier just to equalize and eliminate the difference in cooling effects between the junctions. Approximations
44、 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 stage and zener reference in a separate enclosure. This construction is shown in Fig. 4. The improvement i
45、n 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 protective covers. The unit was operated without the cover until time tl, when the cover was attached. Th
46、e 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. The unit was operated without the cover until time tl, when the cover was attached. The initial voltage c
47、hange 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. Variations of the contact resistance can cause drift. It is not always necessary, however, to resort to the
48、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 corro
