Constant frequency PWM Using 555-Timer
With the basic astable circuit, the duty ratio cannot be controlled without affecting the frequency. Using the above circuit, it is possible to maintain a constant frequency with variable duty cycle. The TON and TOFF durations are individually controlled by placing the bypass diodes. As the Pot type variable resistor is used, the frequency is maintained constant because the total resistance Ra + Rb is constant even if individual portions are varied.
