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单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,1.10,戴维宁定理,1.11,电路中电位的计算,例,有源二端网络,R,L,b,a,R,L,I,1.10,戴维宁定理,求：,I,任意线性有源二端网络,N,，可以用一个恒压源与电阻串联,的支路等效代替。其中恒压源的电动势等于有源二端网络,的开路电压，串联电阻等于有源二端网络所有独立源都不,作用时由端钮看进去的等效电阻。,戴维宁定理,除去独立源：,恒压源短路,恒流源开路,R,0,N,0,a,b,E,=,U,O,N,a,b,+,b,R,L,I,+,E,R,0,U,a,N,+,R,L,U,I,线性,有源,二端,网络,N,a,b,+,电路如图，已知,E,1,=40V,，,E,2,=20V,，,R,1,=,R,2,=4,，,R,3,=13,，试用戴维宁定理求电流,I,3,。,E,1,E,2,R,2,I,3,R,3,+,R,1,+,E,R,0,+,_,R,3,a,b,I,3,a,b,注意：“等效”是指对端口外等效,有源二端网络,等效电源,例,1,解：,(1),断开待求支路求等效电源的电动势,E,电路如图，已知,E,1,=40V,，,E,2,=20V,，,R,1,=,R,2,=4,，,R,3,=13,，试用戴维宁定理求电流,I,3,。,E,1,E,2,R,2,I,3,R,3,+,R,1,+,a,b,R,2,E,1,E,2,+,R,1,+,a,b,+,U,0,I,E,=,U,0,=,E,2,+I,R,2,=20V+2.5,4,V=30V,例,1,解：,(2),求等效电源的内阻,R,0,除去所有电源,（理想电压源短路，理想电流源开路）,电路如图，已知,E,1,=40V,，,E,2,=20V,，,R,1,=,R,2,=4,，,R,3,=13,，试用戴维宁定理求电流,I,3,。,E,1,E,2,R,2,I,3,R,3,+,R,1,a,b,R,2,R,1,a,b,R,0,例,1,解：,(3),画出等效电路求电流,I,3,电路如图，已知,E,1,=40V,，,E,2,=20V,，,R,1,=,R,2,=4,，,R,3,=13,，试用戴维宁定理求电流,I,3,。,E,1,I,1,E,2,I,2,R,2,I,3,R,3,+,R,1,+,a,b,E,R,0,+,_,R,3,a,b,I,3,例,1,已知：,R,1,=5,、,R,2,=5,R,3,=10,、,R,4,=5,E,=12V,、,R,G,=10,试用戴维宁定理求检流计中的电流,I,G,。,有源二端网络,E,+,G,R,3,R,4,R,1,R,2,I,G,R,G,a,b,E,+,G,R,3,R,4,R,1,R,2,I,G,R,G,例,2,解,:(1),求开路电压,U,0,E,U,0,+,a,b,+,R,3,R,4,R,1,R,2,I,1,I,2,E,=,U,o,=,I,1,R,2,I,2,R,4,=1.2,5V0.8,5 V,=2V,解,:,E,U,0,+,a,b,+,R,3,R,4,R,1,R,2,(2),求等效电源的内阻,R,0,R,0,a,b,R,3,R,4,R,1,R,2,解：,(3),求检流计中的电流,I,G,E,R,0,+,_,R,G,a,b,I,G,a,b,E,+,G,R,3,R,4,R,1,R,2,I,G,R,G,E,1,R,3,R,4,R,1,+,R,2,E,2,I,S,I,R,5,求图示电路,中的电流,I,。,已知,R,1,=,R,3,=2,，,R,2,=5,，,R,4,=8,，,R,5,=14,，,E,1,=8V,，,E,2,=5,V,，,I,S,=3,A,。,+,E,1,+,U,0,A,B,R,3,R,1,+,R,2,E,2,I,S,+,R,5,I,3,=14V,U,0,=,I,3,R,3,E,2,+,I,S,R,2,(1),求,U,0,解：,I,3,=,R,1,+,R,3,E,1,=2A,例,3,E,1,R,3,R,4,R,1,+,R,2,E,2,I,S,I,R,5,+,A,B,R,3,R,1,R,2,I,S,E,1,+,E,2,+,解：,(2),求,R,0,R,0,=,(,R,1,/,R,3,)+,R,5,+,R,2,=20,(3),求,I,R,0,+,R,4,E,=,0.5A,I=,R,0,R,5,U,0,=E,R,4,R,0,+,I,B,A,例外情况,：求某些二端网络的等效内阻时，用串、并联的方法则不行。如下图：,A,R,0,C,R,1,R,3,R,2,R,4,B,D,R,6,R,5,I,5,R,1,R,3,+,_,R,2,R,4,U,R,6,如何求,R,0,？,推荐,:,加压求流法,加压求流法,无源,网络,I,U,有源,网络,则,：,求电流,I,步骤：,有源网络,无源网络,外加电压,U,A,R,0,C,R,1,R,3,R,2,R,4,B,D,R,6,U,I,R,1,a,b,c,d,R,2,E,1,E,2,R,3,电路中某一点的电位是指,由这一点到,参考点,的电压,记为“,V,X,”,。,电路的参考点,可以任意选取,通常认为参考点的电位为零,V,a,=,E,1,V,c,=,E,2,V,b,=,I,3,R,3,I,3,若以,d,为参考点，则,:,+,+,1.11,电路中电位的计算,R,1,a,b,c,d,R,2,E,1,E,2,R,3,I,3,+E,1,E,2,简化电路,+,+,d,a,b,c,R,1,R,2,R,3,1.11,电路中电位的计算,图示电路，计算开关,S,断开和,闭合时,A,点的电位,V,A,解,:(1),当开关,S,断开时,(2),当开关闭合时,电路,如图（,b,）,电流,I,2,=0,，,电位,V,A,=0V,。,电流,I,1,=,I,2,=0,，,电位,V,A,=6V,。,2K,A,+,I,1,2k,I,2,6V,(b),2k,+6V,A,2k,S,I,2,I,1,(a),例,4,电路如下图所示，,(1),零电位参考点在哪里？画电路图表示出来。,(2),当电位器,R,P,的滑动触点向下滑动时，,A,、,B,两点的电位增高了还是降低了？,A,+,12V,12V,B,R,P,R,1,R,2,I,解：（,1,）电路如左图，零电位参考点为,+12V,电源的“,”,端与,12V,电源的“,+”,端的联接处。,因为电流,I,减小，所以,A,电位增高、,B,点电位降低。,12V,12V,B,A,R,P,R,2,R,1,（,2,）,V,A,=,IR,1,+12,V,B,=,IR,2,12,例,5,第,P42-48,页习题：,A,：,B,：,
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