| |
| 四、 二极管的等效电路及应用 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
（一）理想二极管等效电路 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
当外加正向电压时，二极管导通，正向压降uD=0,相当于开关闭合；
当外加反向电压时，二极管截止，反向电流IR=0，相当于开关断开。
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
(二）考虑正向压降的等效电路 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
 |
|
|
|
|
|
二极管在充分导通且工作电流不是很大时，可以近似认为UD为常数，用一个直流电压源UD来等效正向导通的二极管。
当外加正向电压大于UD时，二极管导通，开关闭合，二极管两端压降为UD；当外加电压小于UD时，二极管截止，开关断开。
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
（三）二极管电路的应用 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
1.
整流电路
二极管具有单向导电性，利用它可以进行交流电到直流电的转换。
u>0时,
u0=u
二极管D1、D3导通，D2、D4截止；
u<0时, u0=
-u 二极管D2、D4导通，D1、D3截止。 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
桥式全波整流输出电压uO的平均值UO为: |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
 |
|
|
|
|
|
其中U为交流电源u的有效值 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
 |
|
|
|
|
|
负载电阻RL中流过的电流io的平均值Io为流过 |
|
|
|
|
|
|
|
|
每个二极管的平均电流ID为IO的一半。即 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
每个二极管在截止时，它的两端承受的最大反向电压就是交流电源电压u的峰值。记为： |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
 |
|
|
|
|
|
|
|
 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
设计选择二极管时必须满足下列条件: |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
