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Digital oscillator realized with ne555 timer circuit is given in figure bellow.
This kind of digital oscillator is just modification of ne555 astabile multivibrator. The advantage of this modification is that diode provides different charging and discharging path. Since R1 is over bridged with diode, charging path is just R2 and the diode, producing charging time constant to be Ï„=R2Â·C1.
During discharging interval, path is through R1 so discharging time constant is Ï„=R1Â·C1.
Since R1 and R2 can be chosen independently, duty cycle can be arbitrary and it is:
Overall time for charging and discharging is
Frequency of oscillation is:
So only one diode added to ne555 oscillator make possible to have duty cycle lower then 50%.
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