脉冲电路的产生和整形剖析.ppt

4. 用555定时器组成多谐振荡器 一.定义、特点 1.多谐振荡器：在接通电源后,不需外加输入信号,能自动产生矩形波的自激振荡器。因矩形波中含有多种谐波成分，故称多谐振荡器。 2.特点： 振荡后,电路没有稳态,只有两个暂稳态在作交替变化，是无稳态电路。 属于脉冲产生电路。 二.电路组成、工作原理 1、方法 ①先构成施密特触发器; ②加R2在VI和VO之间，VI和地之间接C; 2.电路组成、工作原理 接通VCC后，VCC经R1和R2对C充电。当uc上升到2VCC/3时，uo=0，T导通，C通过R2和T放电，uc下降。当uc下降到VCC/3时，uo又由0变为1，T截止，VCC又经R1和R2对C充电。如此重复上述过程，在输出端uo产生了连续的矩形脉冲。 C R 1 u c 8 4 7 3 6 555 2 5 1 0.01 μ F u o V CC R 2 u c u o t t t wH t wL 0 V CC / 3 2 V CC / 3 0 电路 工作波形 2.电路组成、工作原理 输出高电平脉宽tWH=0.7（R1+R2)C 输出低电平脉宽tWL=0.7R2C 振荡频率f=1/0.7(R1+2R2) C充电时间 C放电时间 C R 1 u c 8 4 7 3 6 555 2 5 1 0.01 μ F u o V CC R 2 u c u o t t t wH t wL 0 V CC / 3 2 V CC / 3 0 电路 工作波形 总结： 分类 图形符号 稳态 参数 特点 应用 施密特触发器 2个 VT+、VT- ①VT+,VT-②正反馈 脉冲整形、波形变换、 脉冲鉴幅 单稳态触发器 1个 脉宽tW ① VI ②tW与VI无关 脉冲整形、延时、 定时 多谐振荡器 0个 周期T 占空比D 无输入信号 产生矩形脉冲 1 1 1—不可重触发单稳态 * 集成定时器的其他应用 1．路灯自动控制器 （1）白天因光线亮，光电三极管3DU的C—E间电阻下降，高触发端⑥脚将 2VCC/3 ，定时器的输出端③脚为低电平，所以灯L不亮。 （2）天黑时，光电管C—E间电阻增大，使低触发端②脚电压小于 ，于是③脚为高电平，灯发光。 * 2．60 s定时电路 当按下定时按钮SB时，低触发端②脚就输入了一个小于 的负脉冲，输出端③脚输出高电平，发光二极管LED亮。而定时器中的放电管V则截止，电源对电容C充电。当电容上电压升高到 时，定时器翻转，③脚输出低电平，LED灭，表示定时结束。 * Once there were two mice. They were friends. One mouse lived in the country; the other mouse lived in the city. After many years the Country mouse saw the City mouse; he said, Do come and see me at my house in the country. So the City mouse went. The City mouse said, This food is not good, and your house is not good. Why do you live in a hole in the field? You should come and live in the city. You would live in a nice house made of stone. You would have nice food to eat. You must come and see me at my house in the city. The Country mouse went to the house of the City mouse. It was a very good house. Nice food was set ready for them to eat. But just as they began to eat they heard a great noise. The City mouse cried, Run! Run! The cat is coming! They ran away quickly and hid. After some time they came out. When they came o