Pulse Generator With Variable Duty Cycle Circuit

Using only one IC and six passive components, this pulse generator has a frequency range of 400 to 4000 Hz and an adjustable duty cycle of 1 to 99%. A threshold detector (ICA) and an integrator (ICB) generate a triangular waveform. A positive voltage at the output of ICA causes the output of ICB to become a negative-going ramp. When the output of this ramp reaches a certain value, ICA, by virtue of its positive-feedback network, changes state; its output becomes negative, and the integrator generates positive ramp. This process continually repeats. A voltage follower (ICC) and a 100-kn potentiometer provide a variable 0.18-V reference voltage.
Pulse Generator With Variable Duty Cycle Circuit - schematic

This reference voltage, along with the triangular waveform, feeds into the positive and negative inputs, respectively, of comparator ICD. You can set the comparator`s trip voltage at any point on the triangular waveform; IOD`s output changes at that point. Varying the reference voltage alters the duty cycle of the comparator`s output by adjusting the potentiometer at the negative input of the integrator, thereby varying the integration time without altering the duty cycle.

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