原创「硬见小百科」几种镜像恒流源电路分析

 2020-9-11 09:56  2070 20 20 分类: PCB 文集: 硬见小百科

<div class="pgc-img" style="margin-top: 0px; margin-bottom: 0px; padding: 0px; border: 0px; font-size: 16px; line- color: rgb(34, 34, 34); overflow-wrap: break-word;  "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "WenQuanYi Micro Hei", "Helvetica Neue", Arial, sans-serif; background-color: rgb(255, 255, 255);"><span style="color: rgb(34, 34, 34);">在改进型差动放大器中，用恒流源取代射极电阻RE，既为差动放大电路设置了合适的静态工作电流，又大大增强了共模负反馈作用，使电路具有了更强的抑制共模信号的能力，且不需要很高的电源电压，所以，恒流源和差动放大电路简直是一对绝配！</span></div><p style="margin: 16px 0px; padding: 0px; border: 0px; color: rgb(34, 34, 34);  "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "WenQuanYi Micro Hei", "Helvetica Neue", Arial, sans-serif; font-size: 16px; background-color: rgb(255, 255, 255); text-align: justify;">恒流源既可以为放大电路提供合适的静态电流，也可以作为有源负载取代高阻值的电阻，从而增大放大电路的电压放大倍数。这种用法在集成运放电路中有非常广泛的应用。本节将介绍常见的恒流源电路以及作为有源负载的应用，为后续内容的学习进行知识储备。</p><p style="margin: 16px 0px; padding: 0px; border: 0px; color: rgb(34, 34, 34);  "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "WenQuanYi Micro Hei", "Helvetica Neue", Arial, sans-serif; font-size: 16px; background-color: rgb(255, 255, 255); text-align: justify;"><span style="margin: 0px; padding: 0px; border: 0px; font-weight: 700;">一、镜像恒流源电路</span></p><p style="margin: 16px 0px; padding: 0px; border: 0px; color: rgb(34, 34, 34);  "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "WenQuanYi Micro Hei", "Helvetica Neue", Arial, sans-serif; font-size: 16px; background-color: rgb(255, 255, 255); text-align: justify;">如图1所示为镜像恒流源电路，它由两只特性完全相同的管子VT0和VT1构成，由于VT0管的c、b极连接，因此UCE0=UBE0，即VT0处于放大状态，集电极电流IC0=β0*IB0。另外，管子VT0和VT1的b-e分别连接，所以它们的基极电流IB0=IB1=IB。设电流放大系数β0=β1=β，则两管集电极电流IC0=IC1=IC=β*IB。可见，由于电路的这种特殊接法，使两管集电极IC1和IC0呈镜像关系，故称此电路为镜像恒流源（IR为基准电流，IC1为输出电流）。</p><div class="pgc-img" style="margin-top: 0px; margin-bottom: 0px; padding: 0px; border: 0px; font-size: 16px; line- color: rgb(34, 34, 34); overflow-wrap: break-word;  "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "WenQuanYi Micro Hei", "Helvetica Neue", Arial, sans-serif; background-color: rgb(255, 255, 255);"><img src="http://p6-tt-ipv6.byteimg.com/large/pgc-image/37c9f4bd659348deb09fef441577e123" img_width="388" img_height="378" style="margin-top: 10px; margin-bottom: 10px; padding: 0px; border: 0px; max-width: 100%; display: block;"><p class="pgc-img-caption" style="margin: 16px 0px; padding: 0px; border: 0px;"></p></div><p style="margin: 16px 0px; padding: 0px; border: 0px; color: rgb(34, 34, 34);  "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "WenQuanYi Micro Hei", "Helvetica Neue", Arial, sans-serif; font-size: 16px; background-color: rgb(255, 255, 255); text-align: center;">图1  镜像恒流源电路</p><p style="margin: 16px 0px; padding: 0px; border: 0px; color: rgb(34, 34, 34);  "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "WenQuanYi Micro Hei", "Helvetica Neue", Arial, sans-serif; font-size: 16px; background-color: rgb(255, 255, 255); text-align: justify;">镜像恒流源电路简单，应用广泛。但是在电源电压一定时，若要求IC1较大，则IR势必增大，电阻R的功耗就增大，这是集成电路中应当避免的；若要求IC1较小，则IR势必也小，电阻R的数值就很大，这在集成电路中很难做到，为此，人们就想到用其他方法解决，这样就衍生出其他电流源电路。</p><p style="margin: 16px 0px; padding: 0px; border: 0px; color: rgb(34, 34, 34);  "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "WenQuanYi Micro Hei", "Helvetica Neue", Arial, sans-serif; font-size: 16px; background-color: rgb(255, 255, 255); text-align: justify;"><span style="margin: 0px; padding: 0px; border: 0px; font-weight: 700;">二、比例恒流源电路</span></p><p style="margin: 16px 0px; padding: 0px; border: 0px; color: rgb(34, 34, 34);  "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "WenQuanYi Micro Hei", "Helvetica Neue", Arial, sans-serif; font-size: 16px; background-color: rgb(255, 255, 255); text-align: justify;">如图2所示为比例恒流源电路，它由两只特性完全相同的管子VT0和VT1构成，两管的发射极分别串入电阻Re0和Re1。比例恒流电路源改变了IC1≈IR的关系，使IC1与IR呈比例关系，从而克服了镜像恒流源电路的缺点。</p><p style="margin: 16px 0px; padding: 0px; border: 0px; color: rgb(34, 34, 34);  "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "WenQuanYi Micro Hei", "Helvetica Neue", Arial, sans-serif; font-size: 16px; background-color: rgb(255, 255, 255); text-align: justify;">与典型的静态工作点稳定电路一样，Re0和Re1是电流负反馈电阻，因此与镜像恒流源电路相比，比例恒流源的输出电流IC1具有更高的稳定性。</p><p style="margin: 16px 0px; padding: 0px; border: 0px; color: rgb(34, 34, 34);  "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "WenQuanYi Micro Hei", "Helvetica Neue", Arial, sans-serif; font-size: 16px; background-color: rgb(255, 255, 255); text-align: justify;">当Re0＝Re1时，IC1仍然等于IR，但此电路的IR由式（2-4）约定，比式（2-2）的IR小，一般用于前置放大器的输入级。</p><div class="pgc-img" style="margin-top: 0px; margin-bottom: 0px; padding: 0px; border: 0px; font-size: 16px; line- color: rgb(34, 34, 34); overflow-wrap: break-word;  "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "WenQuanYi Micro Hei", "Helvetica Neue", Arial, sans-serif; background-color: rgb(255, 255, 255);"><img src="http://p9-tt-ipv6.byteimg.com/large/pgc-image/ba88376d6a764182a29e2b30a6d81576" img_width="362" img_height="378" style="margin-top: 10px; margin-bottom: 10px; padding: 0px; border: 0px; max-width: 100%; display: block;"><p class="pgc-img-caption" style="margin: 16px 0px; padding: 0px; border: 0px;"></p></div><p style="margin: 16px 0px; padding: 0px; border: 0px; color: rgb(34, 34, 34);  "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "WenQuanYi Micro Hei", "Helvetica Neue", Arial, sans-serif; font-size: 16px; background-color: rgb(255, 255, 255); text-align: center;">图2  比例恒流源电路</p><p style="margin: 16px 0px; padding: 0px; border: 0px; color: rgb(34, 34, 34);  "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "WenQuanYi Micro Hei", "Helvetica Neue", Arial, sans-serif; font-size: 16px; background-color: rgb(255, 255, 255); text-align: justify;"><span style="margin: 0px; padding: 0px; border: 0px; font-weight: 700;">三、微变恒流源电路</span></p><p style="margin: 16px 0px; padding: 0px; border: 0px; color: rgb(34, 34, 34);  "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "WenQuanYi Micro Hei", "Helvetica Neue", Arial, sans-serif; font-size: 16px; background-color: rgb(255, 255, 255); text-align: justify;">由式（2-3）可知，若Re0很小甚至于为零，则Re1只采用较小的电阻就能获得较小的输出电流，这种电路称为微变恒流源，如图3所示。集成运放输入级静态电流很小，往往只有几十微安，甚至更小，因此微变电流源主要应用于集成运放输入级的有源负载。</p><div class="pgc-img" style="margin-top: 0px; margin-bottom: 0px; padding: 0px; border: 0px; font-size: 16px; line- color: rgb(34, 34, 34); overflow-wrap: break-word;  "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "WenQuanYi Micro Hei", "Helvetica Neue", Arial, sans-serif; background-color: rgb(255, 255, 255);"><img src="http://p9-tt-ipv6.byteimg.com/large/pgc-image/cc3427cb09304c74a28fc91943d37627" img_width="298" img_height="302" style="margin-top: 10px; margin-bottom: 10px; padding: 0px; border: 0px; max-width: 100%; display: block;"><p class="pgc-img-caption" style="margin: 16px 0px; padding: 0px; border: 0px;"></p></div><p style="margin: 16px 0px; padding: 0px; border: 0px; color: rgb(34, 34, 34);  "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "WenQuanYi Micro Hei", "Helvetica Neue", Arial, sans-serif; font-size: 16px; background-color: rgb(255, 255, 255); text-align: center;">图3  微变恒流源电路</p><p style="margin: 16px 0px; padding: 0px; border: 0px; color: rgb(34, 34, 34);  "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "WenQuanYi Micro Hei", "Helvetica Neue", Arial, sans-serif; font-size: 16px; background-color: rgb(255, 255, 255); text-align: justify;"><span style="margin: 0px; padding: 0px; border: 0px; font-weight: 700;">四、多路恒流源电路</span></p><p style="margin: 16px 0px; padding: 0px; border: 0px; color: rgb(34, 34, 34);  "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "WenQuanYi Micro Hei", "Helvetica Neue", Arial, sans-serif; font-size: 16px; background-color: rgb(255, 255, 255); text-align: justify;">集成运放是一个多级放大电路，因而需要多路恒流源电路分别给各级提供合适的静态电流。可以利用一个基准电流去获得多个不同的输出电流，以适应各级的需要。</p><p style="margin: 16px 0px; padding: 0px; border: 0px; color: rgb(34, 34, 34);  "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "WenQuanYi Micro Hei", "Helvetica Neue", Arial, sans-serif; font-size: 16px; background-color: rgb(255, 255, 255); text-align: justify;">图4所示电路是在比例恒流源基础上得到的多路恒流源电路，IR为基准电流，IC1、IC2和IC3为三路输出电流。由于各管的b-e间电压UBE数值大致相等，因此可得近似关系</p><p style="margin: 16px 0px; padding: 0px; border: 0px; color: rgb(34, 34, 34);  "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "WenQuanYi Micro Hei", "Helvetica Neue", Arial, sans-serif; font-size: 16px; background-color: rgb(255, 255, 255); text-align: justify;">IE0Re0≈IE1Re1≈IE2Re2≈IE3Re3（2-6）</p><p style="margin: 16px 0px; padding: 0px; border: 0px; color: rgb(34, 34, 34);  "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "WenQuanYi Micro Hei", "Helvetica Neue", Arial, sans-serif; font-size: 16px; background-color: rgb(255, 255, 255); text-align: justify;">当IE0确定后，各级只要选择合适的电阻，就可以得到所需的电流。</p><div class="pgc-img" style="margin-top: 0px; margin-bottom: 0px; padding: 0px; border: 0px; font-size: 16px; line- color: rgb(34, 34, 34); overflow-wrap: break-word;  "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "WenQuanYi Micro Hei", "Helvetica Neue", Arial, sans-serif; background-color: rgb(255, 255, 255);"><img src="http://p1-tt-ipv6.byteimg.com/large/pgc-image/0d1b2283c7554b6cb788a86c858c35fc" img_width="427" img_height="302" style="margin-top: 10px; margin-bottom: 10px; padding: 0px; border: 0px; max-width: 100%; display: block;"><p class="pgc-img-caption" style="margin: 16px 0px; padding: 0px; border: 0px;"></p></div><p style="margin: 16px 0px; padding: 0px; border: 0px; color: rgb(34, 34, 34);  "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "WenQuanYi Micro Hei", "Helvetica Neue", Arial, sans-serif; font-size: 16px; background-color: rgb(255, 255, 255); text-align: center;">图4  多路恒流源电路</p><p style="margin: 16px 0px; padding: 0px; border: 0px; color: rgb(34, 34, 34);  "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "WenQuanYi Micro Hei", "Helvetica Neue", Arial, sans-serif; font-size: 16px; background-color: rgb(255, 255, 255); text-align: center;"><span style="margin: 0px; padding: 0px; border: 0px; font-weight: 700;">‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧</span>‧ END <span style="margin: 0px; padding: 0px; border: 0px; font-weight: 700;">‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧</span>‧</p><p style="margin: 16px 0px; padding: 0px; border: 0px; color: rgb(34, 34, 34);  "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "WenQuanYi Micro Hei", "Helvetica Neue", Arial, sans-serif; font-size: 16px; background-color: rgb(255, 255, 255); text-align: center;"><em style="margin: 0px; padding: 0px; border: 0px; font-weight: 700;">免责声明：本文转自网络，版权归原作者所有，如涉及作品版权问题，请及时与我们联系，谢谢！</em></p><p style="margin: 16px 0px; padding: 0px; border: 0px; color: rgb(34, 34, 34);  "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "WenQuanYi Micro Hei", "Helvetica Neue", Arial, sans-serif; font-size: 16px; background-color: rgb(255, 255, 255);"><span style="margin: 0px; padding: 0px; border: 0px; font-weight: 700;">关于硬见科技</span></p><p style="margin: 16px 0px; padding: 0px; border: 0px; color: rgb(34, 34, 34);  "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "WenQuanYi Micro Hei", "Helvetica Neue", Arial, sans-serif; font-size: 16px; background-color: rgb(255, 255, 255); text-align: justify;">硬见科技是国内最具特色的电子工程师社区，融合了行业资讯、社群互动、培训学习、活动交流、设计与制造分包等服务，以开放式硬件创新技术交流和培训服务为核心，连接了超过30万工程师和产业链上下游企业，聚焦电子行业的科技创新，聚合最值得关注的产业链资源， 致力于为百万工程师和创新创业型企业打造一站式公共设计与制造服务平台。</p>

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