What is a PWM?

Question

Can some body explain more details on Pulse Width Module (PWM) ?

Answer 1

PWM stands for pulse width modulation.
It is a square wave signal consisting usually of a fixed frequency, but the width of the individual pulses varies according to some rule.
It could be used to trasmit information (although nobody would use it this way nowadays), and in this case the width of the pulses can be proportional to the voltage of the input signal to be transmitted. At the reception side, a circuit averaging the input signal can recover the original signal.

But PWM is mainly used for switchmode regulators. Transistors are very efficient when they are used as switches (going rapidly from a full-on condition to a full-off condition). Since there is no intermediate state for the transistors, the way of controlling the output voltage is by varying the pulse width (or the relationship of the on-time to the off-time). An inductor-capacitor filter averages the pulses to get a constant voltage at the output, and PWM is used to control the magnitude of that voltage.

Answer 2

Pulse-width modulation (PWM) of a signal or power source involves the modulation of its duty cycle, to either convey information over a communications channel or control the amount of power sent to a load.

Pulse-width modulation uses a square wave whose duty cycle is modulated resulting in the variation of the average value of the waveform.
Three types of pulse-width modulation (PWM) are possible.

The pulse center may be fixed in the center of the time window and both edges of the pulse moved to compress or expand the width.
The lead edge can be held at the lead edge of the window and the tail edge modulated.
The tail edge can be fixed and the lead edge modulated.
Applications:
1.In telecommunications, the widths of the pulses correspond to specific data values encoded at one end and decoded at the other.

Pulses of various lengths (the information itself) will be sent at regular intervals (the carrier frequency of the modulation).

2.Power delivery:
PWM can be used to reduce the total amount of power delivered to a load without losses normally incurred when a power source is limited by resistive means. This is because the average power delivered is proportional to the modulation duty cycle. With a sufficiently high modulation rate, passive electronic filters can be used to smooth the pulse train and recover an average analog waveform
3.PWM is also used in efficient voltage regulators. By switching voltage to the load with the appropriate duty cycle, the output will approximate a voltage at the desired level. The switching noise is usually filtered with an inductor and a capacitor.
4.PWM is sometimes used in sound synthesis, in particular subtractive synthesis, as it gives a nice effect similar to chorus or slightly detuned oscillators played together. (In fact, PWM is equivalent to the difference of two sawtooth waves.

Answer 3

The best example of PWM, pulse width modulation, that I can think of is the fuel injection system in a modern vehicle.
The fuel pressure is maintained at a constant pressure on a normally closed solenoid injector.
The actual time that the injector is spraying fuel depends on the width of the pulse that is sent from the engine control computer to the injector, and this, obviously, determines the exact amount of fuel that each cylinder is receiving. The frequency is synchronized to the engine RPM and the pulse width (the amount of fuel needed) is determined by several inputs.
This method is far and away better at metering fuel than any carburetor(s) system.

Answer 4

a dc current is chopped in order to reduce/vary power output. power out = max power x (time on /time total).