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I need some help please

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hadjaki

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I have an LM555 in 12Vdc and i want to make it have 65duty cycle when i put voltage in pin 5 through a resistor of 10k.and i have to found the voltage to make that duty cycle.And the second one question is:when i change the duty cycle the frequency changes and why?i cant do it please help me
 

audioguru

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Most Helpful Member
I have an LM555 in 12Vdc and i want to make it have 65duty cycle when i put voltage in pin 5 through a resistor of 10k.and i have to found the voltage to make that duty cycle.And the second one question is:when i change the duty cycle the frequency changes and why?i cant do it please help me
The datasheet for the LM555 shows a "PWM Circuit" that is a monostable that has modulation on its pin5 and its frequency does not change. The datasheet also has a "Pulse Position Modulator circuit" that you are using that is an astable oscillator and the modulation on its pin5 changes the duty-cycle and changes the frequency.
 

hadjaki

New Member
re

yeah i know but how can i find the voltage to take 65%duty cycle?in my circuit R1=47K,R2=20K,C1=2.7n and C2=1n(capacitor on pin 5 and ground).
 
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