[电路教桉1.ppt

三、功率 + — uS i ① uS 和 i 的实际方向相反，p = – uS ·i﹤0 电压源提供功率，起“电源”作用。 + — uS i ② uS 和 i 的实际方向相同，p = uS ·i﹥0 电压源吸收功率，起“负载”作用。 Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 特点：1）i 为定值或保持一定的时间函数而不变； 2）u 的大小取决于恒流源本身及与之相联 的外电路； 3）与恒流源串联的元件不影响其电流。 一、理想电流源（恒流源） （Rs = ∞ “开路”） R变，u 变，i 不变的电源 ( i = iS ) i u 0 iS R iS i + – u 二、实际电流源（Rs ≠ ∞） i = u = R·i R↑→ u↑→ i↓ RS愈小，i 愈小，带负载能力愈差（外特性差） 对负载言，RS 愈大愈好（RS 大，带负载能力强） 一般，若 RS ﹥﹥R ，则近似为 恒流源。 0 i is u R iS i + _ u RS ● ● §1—6 电流源 Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 三、功率 ① is u + – iS 和u 的实际方向相反，p = – iS ·u﹤0 电流源提供功率，起“电源”作用。 is u + – ② iS 和u 的实际方向相同，p = iS ·u﹥0 电流源吸收功率，起“负载”作用。 附注：电压源、电流源作为电源或信号输入时，在电路中起 “激励”作用；在电路中产生的电压和电流，这些电压和电流便 是“响应”。 Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 推广—— n 个电阻串联： + + – – u uK R1 R2 RK Rn Rn–1 uk = = §1—7 分压电路和分流电路 一、分压电路 1、串联电阻的分压 如图：u = u1 + u2 = R1·i +R2·i = (R1+R2)·i – R1 R2 i + + + – – u1 u2 u u1 = R1·i = ·u u2 = R2 ·i = ·u ∴ i = Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 2、应用举例 1）作分压器 ● ● ● ● + + + + – – – – 10K 10K 10K 150V 150V 50V 100V ● + + – – R U ｝ RX UX= · U