通信电源为什么是-48V

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<p class="cm4" align="center" style="MARGIN: 0cm 0cm 21.5pt 17pt; TEXT-ALIGN: center; mso-line-height-alt: 15.75pt;"><font face="宋体"><b style="mso-bidi-font-weight: normal;"><span style="FONT-SIZE: 16pt; COLOR: black; mso-ascii-font-family: ˎ̥; mso-hansi-font-family: ˎ̥;">通信电源为什么是</span></b><b style="mso-bidi-font-weight: normal;"><span lang="EN-US" style="FONT-SIZE: 16pt; COLOR: black; FONT-FAMILY: ˎ̥;">-48V</span></b><b><span lang="EN-US" style="FONT-SIZE: 16pt; COLOR: black;"><p></p></span></b></font></p><p class="cm4" style="MARGIN: 0cm 0cm 21.5pt 17pt; WORD-BREAK: break-all; TEXT-INDENT: 11pt; LINE-HEIGHT: 15.75pt; mso-para-margin-top: 0cm; mso-para-margin-right: 0cm; mso-para-margin-bottom: 21.5pt; mso-para-margin-left: 1.62gd; mso-char-indent-count: 1.0;"><span style="FONT-SIZE: 11pt; COLOR: black;"><font face="宋体">这里面包含<span lang="EN-US">2 </span>个意思：<span lang="EN-US">
                                        <p></p></span></font></span></p><p class="default" style="MARGIN: 0cm 0cm 0pt; WORD-BREAK: break-all; LINE-HEIGHT: 15.75pt;"><font face="宋体"><span lang="EN-US" style="FONT-SIZE: 7pt; COLOR: black; FONT-FAMILY: Algerian;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="FONT-SIZE: 11pt; COLOR: black;">（</span></font><span lang="EN-US" style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: Arial;">1</span><span style="FONT-SIZE: 11pt; COLOR: black;"><font face="宋体">） 极性为何是负电源（也就是正接地）？<span lang="EN-US">
                                        <p></p></span></font></span></p><p class="default" style="MARGIN: 0cm 0cm 0pt; WORD-BREAK: break-all; LINE-HEIGHT: 15.75pt;"><font face="宋体"><span lang="EN-US" style="FONT-SIZE: 7pt; COLOR: black; FONT-FAMILY: Algerian;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="FONT-SIZE: 11pt; COLOR: black;">（</span></font><span lang="EN-US" style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: Arial;">2</span><span style="FONT-SIZE: 11pt; COLOR: black;"><font face="宋体">） 电压为何为</font></span><span lang="EN-US" style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: Arial;">-48V</span><span style="FONT-SIZE: 11pt; COLOR: black;"><font face="宋体">（</font></span><span lang="EN-US" style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: Arial;">-36~ -72V</span><span style="FONT-SIZE: 11pt; COLOR: black;"><font face="宋体">）？<span lang="EN-US">
                                        <p></p></span></font></span></p><p class="default" align="center" style="MARGIN: 0cm 0cm 0pt; WORD-BREAK: break-all; LINE-HEIGHT: 15.75pt; TEXT-ALIGN: center;"><span lang="EN-US" style="FONT-SIZE: 11pt; COLOR: black;"><font face="宋体">&nbsp; <p></p></font></span></p><p class="cm5" style="TEXT-JUSTIFY: inter-ideograph; MARGIN: 0cm 0cm 13.25pt 19.9pt; TEXT-INDENT: 19.65pt; LINE-HEIGHT: 22pt; TEXT-ALIGN: justify;"><span style="FONT-SIZE: 11pt; COLOR: black;"><font face="宋体">先说一下第</font></span><span lang="EN-US" style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: Arial;">2 </span><span style="FONT-SIZE: 11pt; COLOR: black;"><font face="宋体">个问题。使用</font></span><span lang="EN-US" style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: Arial;">-48V </span><span style="FONT-SIZE: 11pt; COLOR: black;"><font face="宋体">电源是历史原因造成的。使用最早的通讯网是电话网，话机是由电讯局供电的，选</font></span><span lang="EN-US" style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: Arial;">48V </span><span style="FONT-SIZE: 11pt; COLOR: black;"><font face="宋体">是在当时的条件下尽可能提高用户到端局的距离（</font></span><span lang="EN-US" style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: Arial;">36V </span><span style="FONT-SIZE: 11pt; COLOR: black;"><font face="宋体">是安全电压，超过太多不安全）。后来为了兼容早期设备、降低成本考虑，局端通讯设备还是用</font></span><span lang="EN-US" style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: Arial;">-48V </span><span style="FONT-SIZE: 11pt; COLOR: black;"><font face="宋体">电源。<span lang="EN-US">
                                        <p></p></span></font></span></p><p class="cm5" style="TEXT-JUSTIFY: inter-ideograph; MARGIN: 0cm 0cm 13.25pt 19.9pt; TEXT-INDENT: 19.65pt; LINE-HEIGHT: 22pt; TEXT-ALIGN: justify;"><span style="FONT-SIZE: 11pt; COLOR: black;"><font face="宋体">同样，采用负电源系统，正极接地只是约定俗成。原来有个说法是空气中有大量的负电荷，根据电化学常识，正极接地可以吸附空气中的负离子，从而保护电信设备的外壳不被锈蚀。其实这种说法不是很对。原电池反应和电解反应是会导致设备生锈，但是因为它们在设备上是以微观形式存在的，几乎没有影响。例如非通讯系统的网络都是负极接地（例如您正在使用的计算机），但是并没有生锈。并且</font></span><span lang="EN-US" style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: Arial;">-48V </span><span style="FONT-SIZE: 11pt; COLOR: black;"><font face="宋体">内部都通过</font></span><span lang="EN-US" style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: Arial;">DC/DC </span><span style="FONT-SIZE: 11pt; COLOR: black;"><font face="宋体">隔离，</font></span><span lang="EN-US" style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: Arial;">DC/DC </span><span style="FONT-SIZE: 11pt; COLOR: black;"><font face="宋体">输出的就是负极接地，也没有看到单板腐蚀生锈。所以不论哪个极接地，都是一样的。<span lang="EN-US">
                                        <p></p></span></font></span></p><p class="cm1" style="TEXT-JUSTIFY: inter-ideograph; MARGIN: 0cm 0cm 0pt 19.9pt; TEXT-INDENT: 19.65pt; LINE-HEIGHT: 15.75pt; TEXT-ALIGN: justify;"><span style="FONT-SIZE: 11pt; COLOR: black;"><font face="宋体">至于设备的外壳接地（接</font></span><span lang="EN-US" style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: Arial;">GND </span><span style="FONT-SIZE: 11pt; COLOR: black;"><font face="宋体">），这是出于保护性的目的，将设备上累积的电荷快速泻放到大地，从而不会损伤设备和工作人员。<span lang="EN-US">
                                        <p></p></span></font></span></p><p class="cm5" style="TEXT-JUSTIFY: inter-ideograph; MARGIN: 0cm 5.65pt 13.25pt 19.65pt; TEXT-INDENT: 22pt; LINE-HEIGHT: 22pt; TEXT-ALIGN: justify; mso-para-margin-top: 0cm; mso-para-margin-right: 5.65pt; mso-para-margin-bottom: 13.25pt; mso-para-margin-left: 1.87gd; mso-char-indent-count: 2.0;"><font face="宋体"><span style="FONT-SIZE: 11pt; COLOR: black;">大家的产品基本上都是使用</span><span lang="EN-US" style="FONT-SIZE: 11pt; COLOR: black; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">-48V </span><span style="FONT-SIZE: 11pt; COLOR: black;">电源系统，一般测到的实际电压是</span></font><span lang="EN-US" style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: Arial; mso-fareast-font-family: &quot;mso-ascii-font-family:&quot;;">–</span><font face="宋体"><span lang="EN-US" style="FONT-SIZE: 11pt; COLOR: black; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">53.5V </span><span style="FONT-SIZE: 11pt; COLOR: black;">。这是因为出于可靠考虑，通讯设备都带有备用电池（</span></font><span lang="EN-US" style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: Arial;">-48v</span><span style="FONT-SIZE: 11pt; COLOR: black;"><font face="宋体">） ，为了保证电池的可靠充电，供电电压需要略高于电池电压。<span lang="EN-US">
                                        <p></p></span></font></span></p><p class="cm5" style="TEXT-JUSTIFY: inter-ideograph; MARGIN: 0cm 5.65pt 13.25pt 19.65pt; TEXT-INDENT: 22pt; LINE-HEIGHT: 22pt; TEXT-ALIGN: justify; mso-para-margin-top: 0cm; mso-para-margin-right: 5.65pt; mso-para-margin-bottom: 13.25pt; mso-para-margin-left: 1.87gd; mso-char-indent-count: 2.0;"><span style="FONT-SIZE: 11pt; COLOR: black;"><font face="宋体">通过媒介可能还会了解到有使用</font></span><span lang="EN-US" style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: Arial;">-24V </span><span style="FONT-SIZE: 11pt; COLOR: black;"><font face="宋体">电源系统的设备，这是现代一些内部设备为设计方便而使用的。一般测量到电源的输出电压</font></span><span lang="EN-US" style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: Arial;">26.8V </span><span style="FONT-SIZE: 11pt; COLOR: black;"><font face="宋体">。<span lang="EN-US">
                                        <p></p></span></font></span></p><p class="cm3" style="TEXT-JUSTIFY: inter-ideograph; MARGIN: 0cm 9.65pt 48.9pt 19.65pt; TEXT-INDENT: 22pt; LINE-HEIGHT: 22.15pt; TEXT-ALIGN: justify; mso-para-margin-top: 0cm; mso-para-margin-right: 9.65pt; mso-para-margin-bottom: 48.9pt; mso-para-margin-left: 1.87gd; mso-char-indent-count: 2.0;"><font face="宋体"><span style="FONT-SIZE: 11pt; COLOR: black;">一般要求设备在电压波动范围<span lang="EN-US">±</span></span><span lang="EN-US" style="FONT-SIZE: 11pt; COLOR: black; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">20% </span><span style="FONT-SIZE: 11pt; COLOR: black;">内工作正常。对</span><span lang="EN-US" style="FONT-SIZE: 11pt; COLOR: black; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">-48V </span><span style="FONT-SIZE: 11pt; COLOR: black;">系统设备就是要求工作电压范围</span><span lang="EN-US" style="FONT-SIZE: 11pt; COLOR: black; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">-38.4V ~ 57.6V</span><span style="FONT-SIZE: 11pt; COLOR: black;">，但是大家实际上一般要求工作范围</span></font><span lang="EN-US" style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: Arial; mso-fareast-font-family: &quot;mso-ascii-font-family:&quot;;">–</span><font face="宋体"><span lang="EN-US" style="FONT-SIZE: 11pt; COLOR: black; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">36V ~ -72V </span><span style="FONT-SIZE: 11pt; COLOR: black;">。主要是考虑</span><span lang="EN-US" style="FONT-SIZE: 11pt; COLOR: black; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">-48V </span><span style="FONT-SIZE: 11pt; COLOR: black;">系统设备要兼容</span></font><span lang="EN-US" style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: Arial; mso-fareast-font-family: &quot;mso-ascii-font-family:&quot;;">–</span><font face="宋体"><span lang="EN-US" style="FONT-SIZE: 11pt; COLOR: black; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">60V </span><span style="FONT-SIZE: 11pt; COLOR: black;">电源系统，它要求</span></font><span lang="EN-US" style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: Arial; mso-fareast-font-family: &quot;mso-ascii-font-family:&quot;;">–</span><font face="宋体"><span lang="EN-US" style="FONT-SIZE: 11pt; COLOR: black; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">48~ -72V </span><span style="FONT-SIZE: 11pt; COLOR: black;">。这样取合集就是就是要求工作电压范围约</span><span lang="EN-US" style="FONT-SIZE: 11pt; COLOR: black; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">-36V ~ -72V </span><span style="FONT-SIZE: 11pt; COLOR: black;">。<span lang="EN-US">
                                        <p></p></span></span></font></p><p class="cm5" style="TEXT-JUSTIFY: inter-ideograph; MARGIN: 0cm 0cm 13.25pt; TEXT-INDENT: 19.65pt; LINE-HEIGHT: 22pt; TEXT-ALIGN: justify;"><font face="宋体"><span style="FONT-SIZE: 11pt; COLOR: black;">顺便提一下，</span><span lang="EN-US" style="FONT-SIZE: 11pt; COLOR: black; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">-48V </span><span style="FONT-SIZE: 11pt; COLOR: black;">电源系统只是我国和大部分国家采用的通信电源标准，并非所有国家都使用这个标准，例如俄罗斯会使用</span><span lang="EN-US" style="FONT-SIZE: 11pt; COLOR: black; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">-60V </span><span style="FONT-SIZE: 11pt; COLOR: black;">的电源系统，还有某些国家使用</span><span lang="EN-US" style="FONT-SIZE: 11pt; COLOR: black; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">-24V </span><span style="FONT-SIZE: 11pt; COLOR: black;">的电源系统。如果产品要在这些地区销售，就要兼顾这些不同的标准。<span lang="EN-US">
                                        <p></p></span></span></font></p><p class="cm2" style="TEXT-JUSTIFY: inter-ideograph; MARGIN: 0cm 5.65pt 0pt 0cm; TEXT-INDENT: 19.65pt; LINE-HEIGHT: 15.75pt; TEXT-ALIGN: justify;"><font face="宋体"><span style="FONT-SIZE: 11pt; COLOR: black;">市电的标准在世界范围内也是不同的，例如我国和欧洲等采用</span><span lang="EN-US" style="FONT-SIZE: 11pt; COLOR: black; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">220V </span><span style="FONT-SIZE: 11pt; COLOR: black;">的市电系统，美国、日本等是</span><span lang="EN-US" style="FONT-SIZE: 11pt; COLOR: black; mso-hansi-font-family: Arial; mso-bidi-font-family: Arial;">110V </span><span style="FONT-SIZE: 11pt; COLOR: black;">的市电。<span lang="EN-US">
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