555 Timer Duty Cycle
in [Basics]
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From: Michael on 15 Feb 2007 14:59 Hi, 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? Cheers, Michael *http://www.scienceprog.com/control-motor-pwm-schematic/
From: Tom Biasi on 15 Feb 2007 16:02 "Michael" <QmQiQcQhQaQeQlQhQiQmQsQ(a)QbQlQuQeQyQoQnQdQeQrQ.QcQoQ.QuQkQ> wrote in message news:UY2Bh.331518$MO2.233503(a)fe3.news.blueyonder.co.uk... > Hi, > > I'm trying to use a 555 timer to produce a PWM waveform however can't find > any reference as to how the value of the resistor* can be used to calcuate > the duty cycle. Is there a formula that says something like when you use > Xohms it gives 2X% duty cycle? > > Cheers, > > Michael > > *http://www.scienceprog.com/control-motor-pwm-schematic/ > Bill has a calculator. http://ourworld.compuserve.com/homepages/Bill_Bowden/555.htm
From: Michael on 15 Feb 2007 17:21 "Tom Biasi" <tombiasi@********optonline.net> wrote in message news:GT3Bh.20$Ao5.4(a)newsfe09.lga... > > "Michael" <QmQiQcQhQaQeQlQhQiQmQsQ(a)QbQlQuQeQyQoQnQdQeQrQ.QcQoQ.QuQkQ> > wrote in message news:UY2Bh.331518$MO2.233503(a)fe3.news.blueyonder.co.uk... >> Hi, >> >> I'm trying to use a 555 timer to produce a PWM waveform however can't >> find any reference as to how the value of the resistor* can be used to >> calcuate the duty cycle. Is there a formula that says something like when >> you use Xohms it gives 2X% duty cycle? >> >> Cheers, >> >> Michael >> >> *http://www.scienceprog.com/control-motor-pwm-schematic/ >> > > Bill has a calculator. > > http://ourworld.compuserve.com/homepages/Bill_Bowden/555.htm > > Hi, Thanks, I've put the formula into Excel and everytime I change of the values (R1,R2,C1) it changes both the frequency and duty cycle. Is there a way to change only the duty cycle once you have the frequency you want? Cheers, Michael
From: Lord Garth on 15 Feb 2007 17:46 "Michael" <QmQiQcQhQaQeQlQhQiQmQsQ(a)QbQlQuQeQyQoQnQdQeQrQ.QcQoQ.QuQkQ> wrote in message news:H15Bh.332045$MO2.127057(a)fe3.news.blueyonder.co.uk... > > "Tom Biasi" <tombiasi@********optonline.net> wrote in message > news:GT3Bh.20$Ao5.4(a)newsfe09.lga... > > > > "Michael" <QmQiQcQhQaQeQlQhQiQmQsQ(a)QbQlQuQeQyQoQnQdQeQrQ.QcQoQ.QuQkQ> > > wrote in message news:UY2Bh.331518$MO2.233503(a)fe3.news.blueyonder.co.uk... > >> Hi, > >> > >> 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? > >> > >> Cheers, > >> > >> Michael > >> > >> *http://www.scienceprog.com/control-motor-pwm-schematic/ > >> > > > > Bill has a calculator. > > > > http://ourworld.compuserve.com/homepages/Bill_Bowden/555.htm Look to alt.binaries,schematics.electronic for an attached file... > > > > > Hi, > > 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? > > Cheers, > > Michael > >
From: Phil Allison on 15 Feb 2007 18:49
"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 |