LM339 Oscillator Circuit

This Oscillator Circuit designed by using IC LM339 From Texas Instruments. This IC is primarily created to compare two input voltages and generate a corresponding output. It is basically a Quad comparator IC, meaning we can find four numbers of individual voltages comparators in a single 14-pin package of LM339 IC. This circuit operates with 6 Volts DC supply.

By using Variable Resistor instead of R5 Resistor, we can achieve different ranges of output frequency. By using wave shaping circuit we can modify the output square pulse depends on our requirements.

Circuit Diagram


1U2B ICLM 3391

Construction and Working

The IC LM 339 comparator circuit that generates a rectangular output waveform using an RC timing network connected to the inverting input of the comparator and a voltage divider network connected to the other Non-inverting input.

Firstly, lets assume that the capacitor is fully charged and the output of the comparator is saturated at the positive supply. The capacitor C1 starts to charge up from the output voltages Vout through resistor R5 act as a rate determined by their RC time constant. However, as soon as the capacitors charging voltage at the comparator inverting is equal to or greater than the voltage at the Non-inverting terminal output voltage fraction divided between resistor R1 and R2 the output will changes state and the driven to the opposing negative supply.

But the capacitor which has been charging towards the positive supply, now sees a negative voltage, across its plates. This sudden reversal of the output voltage causes the capacitor to discharge towards the new value of Vout at a rate dictated again by their RC time constant.

Resistor R5 and capacitor C1 work like the timing network determines the frequency the oscillation.


R-Feedback Resistance in ohms.

f-oscillator output frequency in Hertz.

C-Feedback capacitance.

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