13-09-2017, 10:51 AM
Pulse width modulation (PWM) uses digital signals to control power applications, as well as being fairly easy to convert back to analog with minimal hardware.
Analog systems, such as linear power supplies, tend to generate a lot of heat because they are basically variable resistors that carry a lot of current. Digital systems generally do not generate as much heat. Almost all the heat generated by a switching device is during the transition (which is done quickly), while the device is neither on nor off, but intermediate. This is because the power follows the following formula:
P = E I, or Watts = Voltage X Current
If the voltage or current is near zero, then the power will be close to zero. PWM makes the most of this fact.
PWM can have many of the features of an analog control system, in which the digital signal can be freewheel. PWM does not have to capture data, although there are exceptions to this with the higher end controllers.
One of the parameters of any square wave is the duty cycle. Most square waves are 50%, this is the norm when discussing them, but they do not have to be symmetrical. The on time can be completely varied between the signal being off to be fully on, 0% to 100%, and all ranges between.
Examples of a 10%, 50% and 90% duty cycle are shown below. While the frequency is the same for each one, this is not a requirement.
Analog systems, such as linear power supplies, tend to generate a lot of heat because they are basically variable resistors that carry a lot of current. Digital systems generally do not generate as much heat. Almost all the heat generated by a switching device is during the transition (which is done quickly), while the device is neither on nor off, but intermediate. This is because the power follows the following formula:
P = E I, or Watts = Voltage X Current
If the voltage or current is near zero, then the power will be close to zero. PWM makes the most of this fact.
PWM can have many of the features of an analog control system, in which the digital signal can be freewheel. PWM does not have to capture data, although there are exceptions to this with the higher end controllers.
One of the parameters of any square wave is the duty cycle. Most square waves are 50%, this is the norm when discussing them, but they do not have to be symmetrical. The on time can be completely varied between the signal being off to be fully on, 0% to 100%, and all ranges between.
Examples of a 10%, 50% and 90% duty cycle are shown below. While the frequency is the same for each one, this is not a requirement.