"One week to finish the model electricity" - 55 timer

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Preface

555 Timer is a kind of medium scale integrated circuit with convenient application , It is widely used in signal generation 、 Transformation 、 Control and detection , There are three inside 5k resistance , So called 555 Timer ：

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One 、555 How the timer works

Two 、555 Built multivibrator

At the beginning of capacitor power supply charging ,
1、 In limine VTR The terminal voltage is at [0,1/3VCC], Then the output port outputs high level
2、 The capacitor continuously supplies power VTR The terminal voltage is at [1/3VCC,2/3VCC], The output end remains
3、VTR The terminal voltage is at [1/3VCC,2/3VCC], Now the triode is on , Discipline 7 Start discharging at this time ,VTR The voltage value decreases , Back to the State 2 The output end remains ;
It goes round and round , It can output oscillation signal .
The first transient state is tp1=0.7（R1+R2)C; The second transient state is tp2=0.7R2C
The first transient state is 1/3VCC Boost to 2/3VCC Time for ; The second transient state is 2/3VCC Depressurize to 1/3VCC Time for .
The oscillation period is 0.7(R1+2R2)C.
It can be seen that the duty cycle of the generated pulse signal is always greater than 0.5;
How can the duty cycle be adjusted ？

The simulation diagram is as follows ：

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3、 ... and 、 from 555 A monostable circuit composed of timers

The reference circuit given by the data manual ：

circuit analysis ：