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# Adjustable Duty cycle 555 Square wave Generator

2015-02-02 06:17
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As shown in the figure 3-4, as soon as the voltage VDD is connected, the oscillator starts up. At the beginning of being powered, as the voltage can not be changed suddenly, that is, the starting level of pin 2 is the earth potential, in order to position 555 and leave pin 3 in a state of high level. C charges itself through Ra and D1, the charge time tc=0.693RaC. When the voltage on C reaches threshold level, that is 2/3 VDD, pin 3 is in a low level. At that time, C discharges through the discharge tube in D1,Rb and 555. The discharge time Td=0.693RbC. Suppose the duty cycle is D, then D=tc/Td=Ra/Ra+Rb Adjust RP1, when the center part slide to top, 　　　　　　　　　　Dmin=tc/T=1k/1k+11K≈8.3% When center part of RP1 slide to bottom, Dmax=11K/11K+1K≈91.7% Figure3-4 Adjustable Duty cycle Square wave Generator Figure3-5 Large-scalechangeable Duty cycle Square wave Generator

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