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:
| Note | The human ear can hear frequencies up to roughly 20kHz. When using PWM at frequencies below this, the device being driven can often be heard to buzz. Higher frequencies avoid this. |
| Note | When controlling motors, much greater PWM efficiency is achieved at frequencies above 20-30 kHz. This is because the current (induction) in the windings of the motors doesn't get a chance to collapse and leave the motor when the OFF-period is short. The collaps of this induction field takes some time; driving the motors at high PWM frequencies keeps this induction current in the motors at all times, resulting in much higher efficiencies. |
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