Rectangular Wave - PWM Waveform - Generation using 555

This simple circuit that produces a rectangular waveform using the most commonly available analog timer IC 555.

The on time and off time are controlled by the resistances Ra & Rb, which are variable to get the required value.

The formula for the time calculations are

The Circuit diagram is

The rectangular/pwm output is at pin 3 of the IC.
Resistance R1,R2 protects the device from shorting the terminals to VCC and ensure a minimum resistance available between the terminals.

The time delay depends on C2, RV1 & RV2. Change the values for desired output.

To get a square wave output, the condition is Ra=Rb. To get this, set the both pots to extreme left of right.

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