PULSE_GENERATOR_WITH_VARIABLE_DUTY_CYCLE

Published:2009/6/17 21:59:00 Author:May | From:SeekIC

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 in-tegrator (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 net-work, changes state; its output becomes nega-tive, and the integrator generates positive ramp.This process continually repeats. A voltage fol-lower (ICC) and a 100-kO potentiometer provide a variable ±18-V reference voltage. 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; ICD'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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