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Variable Frequency And Duty Cycle

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BrownOut

Banned
A recent discussion on a circuit with which frequency and duty cycle can be varied independent of each other was the inspiration for the attached circuit. R10 and R15 are intended to model a variable resistor with the input connected to the wiper. This controls the duty cycle. Frequency is controlled independently via R9. In the simulation, two discreet frequencies are chosen by R9, and duty cycle is set to approximately 66%. The duty cycle is visably unaffected by the frequency.

The advantage of this curcuit is the output is taken from the timer, and exploits the excellent characteristics of the timer's output stage. Another point is an application might requre the variable duty cycle period start coincedent with the timer's period. That can not be achieved by using a comparator connected to the timer's capacitor, as in other designs.
 

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  • VarFreq&Duty.JPG
    VarFreq&Duty.JPG
    178.4 KB · Views: 466

Roff

Well-Known Member
Here's a similar idea that I was working on last week.
I have included the .ASC file, so anyone with LTspice can simulate it.
 

Attachments

  • independent Freq & D.C. with cap mult.PNG
    independent Freq & D.C. with cap mult.PNG
    32.4 KB · Views: 559
  • 555 astable with cap multiplier.asc
    3.3 KB · Views: 190

BrownOut

Banned
I've never seen the capacitance multiplier before.
 
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