A Simple PWM Circuit Based on the 555 Timer

A Simple PWM Circuit Based on the 555 Timer - A SIMPLE PWM...

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A SIMPLE PWM CIRCUIT BASED ON THE 555 TIMER November 2005 , Written by  Rick Bickle One of the most fundamental problems in robotics is DC motor speed control. The most common method of speed control is PWM or pulse width modulation. Pulse width modulation is the process of switching the power to a device on and off at a given frequency, with varying on and off times. These on and off times are referred to as "duty cycle". The diagram below shows the waveforms of 10%, 50%, and 90% duty cycle signals. As you can see from the diagram, a 10% duty cycle signal is on for 10% of the wavelength and off for 90%, while a 90% duty cycle signal is on for 90% and off for 10%. These signals are sent to the motor at a high enough frequency that the pulsing has no effect on the motor. The end result of the PWM process is that the overall power sent to the motor can be adjusted from off (0% duty cycle) to full on (100% duty cycle) with good efficiency and stable control. While many robot builders use a microcontroller to generate the required PWM signals, the 555 PWM circuit explained here will give the novice robot builder an easy to construct circuit, and good understanding of pulse width modulation. It is also useful in a variety of other applications where the PWM setting need only be changed occasionally. The 555 timer in the PWM circuit is configured as an astable oscillator. This means that once power is applied, the
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This note was uploaded on 05/04/2009 for the course COMMUNICAT ee526 taught by Professor Mousamousa during the Spring '09 term at Alexandria University.

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A Simple PWM Circuit Based on the 555 Timer - A SIMPLE PWM...

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