| Description of Pulse Width Modulation |
Last Modified: 2007-11-12
PWM or Pulse Width Modulation refers to the concept of rapidly pulsing the digital signal of a wire to simulate a varying voltage on the wire. This method is commonly used for driving motors, heaters, or lights in varying intensities or speeds.
A few terms are associated with PWM:
In the above diagram, the duty cycle is shown at 50%. The pink line shows the average output and you can see that at 50% duty cycle, the output averages is roughly 6V or 50% of full power. Below is a diagram of what a 25% duty cycle PWM signal looks like:
Example of a 25 percent duty cycle.
PWM signals may also be used to approximate time-varying analogue signals. This can be seen in the graph below, where a PWM wave varying from a roughly 25% to a 75% cycle approximates a sinusoidal wave. The actual output, in blue, does not attempt to perfectly mimic a sine wave, but rather form a set of local averages which act as a sine wave.
A simple method of obtaining the characteristics of the PWM signal is to split the analogue signal into a number of discrete segments equal to the length of the PWM period. Then, the PWM cycle for this period can be set equal to the average of the analogue signal over this same interval.
Accuracy varies with
A PWM used to generate a varying analogue equivalent. Taken from Wikipedia; used under the GPL.
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