555 Timer Duty Cycle
in [Basics]
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From: Michael on 16 Feb 2007 06:22 "Phil Allison" <philallison(a)tpg.com.au> wrote in message news:53k9s7F1tfe9iU1(a)mid.individual.net... > > "Michael" >>>> >>>> I'm trying to use a 555 timer to produce a PWM waveform however can't >>>> find any reference as to how the value of the resistor* can be used to >>>> calcuate the duty cycle. Is there a formula that says something like >>>> when you use Xohms it gives 2X% duty cycle? >>>> >> >> Thanks, I've put the formula into Excel and everytime I change of the >> values (R1,R2,C1) it changes both the frequency and duty cycle. Is there >> a way to change only the duty cycle once you have the frequency you want? >> > > > ** Not possible by varying only one resistor. > > A pot will do it: > > http://www.cpemma.co.uk/555pwm.html > > > > > ......... Phil > Thanks guys, Michael |