Pulse

Pulse-width modulation From Wikipedia, the free encyclopedia. (Redirected from Pulse width modulation) This article does not cite its references or sources. You can help Wikipedia by adding appropriate ones. Pulse-width modulation 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.

Contents [hide] • • • •

1 Telecommunications 2 Power delivery 3 Voltage Regulation 4 Audio effects

5 See also [edit] •

Telecommunications In telecommunications, the width of the pulses correspond with 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).

Clock

Data

_ _ _ _ _ _ _ _ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | __| |____| |____| |____| |____| |____| |____| |____| |____

_ __ ____ ____ _ | | | | | | | | | | | | | | | | | | | | _________| |____| |___| |________| |_| |___________

Data

0

1

2

4

0

4

1

0

The inclusion of a clock signal is not necessary as the leading edge of the data signal can be used as the clock if a small offset is added to the data value in order to avoid the lack of a pulse for zero values. [edit]

Power delivery PWM is also used to vary the total amount of power delivered to a load without the losses normally incurred when a power source drops its output voltage through resistive means. In a PWM system the solid state switch being used to control the flow of current is either not conducting any current or has very low voltage drop across it (and is conducting high current); since the instantaneous power dissipated in the switch is the product of the current and the voltage at any given time, this means no power would be dissipated if the switch were ideal. With a sufficiently high modulation rate, simple RC filters are often used to smooth the pulse train into a steady analog voltage. This method is commonly used in DC motor speed control. PWM power limits are also used in the simple light dimmers common in homes. In this case the electricity being modulated is AC. Simple adjustment to the brightness of the light can be implemented by setting at what voltage in the AC cycle the dimmer begins to conduct electricity to the light bulb (using a triac). Because the duty cycle of the modulation is the same as the AC frequency of the line (60hz in the United States) the human eye sees only the average intensity (see flicker fusion). [edit]

Voltage Regulation (main article: switched-mode power supply) 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. One method measures the output voltage. When it is lower than the desired voltage, it turns on the switch. When the output voltage is above the desired voltage, it turns off the switch.

[edit]

Audio effects 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. The ratio between the high and low level is typically modulated with a low frequency oscillator, or LFO. A new class of audio amplifiers based on the PWM principle is becoming popular. Called "Class-D amplifiers", these amplifiers produce a PWM equivalent of the analogue input signal which is fed to the loudspeaker via a suitable filter network to recover the original audio. These amplifiers are characterised by very good efficiency figures (>= 90%) and compact size/light weight for large power outputs. [edit]

See also • • • • • •

Modulation Pulse-code modulation Pulse-amplitude modulation Pulse-density modulation Pulse-position modulation Radio control

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Duty cycle From Wikipedia, the free encyclopedia. In telecommunication, the term duty cycle has the following meanings: In an ideal pulse train, that is, one having rectangular pulses, the ratio of the pulse duration to the pulse period. •

Note: For example, the duty cycle is 0.25 for a pulse train in which the pulse duration is 1 μs and the pulse period is 4 μs.

The ratio of (a) the sum of all pulse durations during a specified period of continuous operation to (b) the total specified period of operation. •

In a continuously variable slope delta (CVSD) modulation converter, the mean proportion of binary "1" digits at the converter output in which each "1" indicates a run of a specified number of consecutive bits of the same polarity in the digital output signal. •

In a periodic phenomenon, the ratio of the duration of the phenomenon in a given period to the period. •

Note: In a piece of electrical equipment, for example, an electric motor, the period for which it may be operated without deleterious effects, for example, from overheating.