Rectangular Pulse Generator with Independent Frequency and Duty Cycle Control

Texas Instruments CD4070B CD4077B CD40106B

Michael Shustov, Tomsk

A diagram of a rectangular pulse generator with independent frequency control from 1 to 10 kHz and duty cycle from 0 to 100% is given.

The problem of designing impulsers with independent pulse frequency adjustment and their pulse ratio (or duty cycle), despite its applicability, has been difficult to solve up to the present time.

China PCB Prototype and Fabrication Manufacturer

Figure 1 depicts an option of the independent frequency adjustment and duty cycle impulser, operating at the frequency from 1 to 10 kHz. The impulser is made on element DD1.1 CMOS of chip CD40106. Its frequency characteristics are set by elements RC: capacitor C1 and a set of resistors and potentiometers R1-R5. With potentiometer R5, it is possible to change the generation frequency smoothly. Resistor R4 limits its upper value.

Independent frequency adjustment and duty cycle impulser.
Figure 1. Independent frequency adjustment and duty cycle impulser.

Chain R1-R3 is connected in parallel to chain R4, R5, but does not affect the generation frequency. From the slider of potentiometer R2, a sawtooth signal, taken off capacitor C1, comes on threshold element input DD1.2, forming a signal adjustable in duration at its output. From the outputs of elements DD1.1 and DD1.2 the signals come on the inputs of element “XOR exclusive OR” DD2.1 of chip CD4070 (or “XNOR exclusive NOR”) of chip CD4077. As a result, the duty factor can be adjusted from 0 to 100% at the device’s output, regardless of frequency. The coefficient adjustment range is set by the clipping resistors R1 (lower range) and R3 (upper range value).

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