An example of PWM in an idealized inductor driven by a ■ voltage source modulated as a series of pulses, resulting in a ■ sine-like current in the inductor. The rectangular voltage pulses nonetheless result in a more and more smooth current waveform, as the switching frequency increases. Note that the current waveform is the integral of the voltage waveform. Pulse-width modulation ( PWM), or pulse-duration modulation ( PDM), is a technique used to encode a into a.

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Although this modulation technique can be used to encode information for transmission, its main use is to allow the control of the power supplied to electrical devices, especially to loads such as motors. In addition, PWM is one of the two principal algorithms used in solar battery chargers, the other being. The average value of (and ) fed to the is controlled by turning the switch between supply and load on and off at a fast rate.

The longer the switch is on compared to the off periods, the higher the total power supplied to the load. The PWM switching frequency has to be much higher than what would affect the load (the device that uses the power), which is to say that the resultant waveform perceived by the load must be as smooth as possible. The rate (or frequency) at which the power supply must switch can vary greatly depending on load and application, for example Switching has to be done several times a minute in an electric stove; 120 in a lamp dimmer; between a few kilohertz (kHz) and tens of kHz for a motor drive; and well into the tens or hundreds of kHz in audio amplifiers and computer power supplies.

The term describes the proportion of 'on' time to the regular interval or 'period' of time; a low duty cycle corresponds to low power, because the power is off for most of the time. Duty cycle is expressed in percent, 100% being fully on. The main advantage of PWM is that power loss in the switching devices is very low.

When a switch is off there is practically no current, and when it is on and power is being transferred to the load, there is almost no voltage drop across the switch. Power loss, being the product of voltage and current, is thus in both cases close to zero. PWM also works well with digital controls, which, because of their on/off nature, can easily set the needed duty cycle. PWM has also been used in certain where its duty cycle has been used to convey information over a communications channel.

Pulse-W idth Modulation Inverters Pulse-width modulation is the process of modifying the width of the pulses in a pulse train in direct proportion to a small control. Pulse Width Modulation for Power Converters Principles and Practice.pdf - Ebook download as PDF File (.pdf), Text File (.txt) or read book online.

Contents. History Some machines (such as a motor) require partial or variable power. In the past, control (such as in a sewing machine's foot pedal) was implemented by use of a connected in series with the motor to adjust the amount of current flowing through the motor. It was an inefficient scheme, as this also wasted power as heat in the resistor element of the rheostat, but tolerable because the total power was low. While the rheostat was one of several methods of controlling power (see and for more info), a low cost and efficient power switching/adjustment method was needed. This mechanism also needed to be able to drive motors for fans, pumps and, and needed to be compact enough to interface with lamp dimmers. PWM emerged as a solution for this complex problem.

One early application of PWM was in the X10, a 10 W audio amplifier available in kit form in the 1960s. At around the same time PWM started to be used in AC motor control. Of note, for about a century, some variable-speed electric motors have had decent efficiency, but they were somewhat more complex than constant-speed motors, and sometimes required bulky external electrical apparatus, such as a bank of variable power resistors or rotating converters such as the. Principle. 2: A simple method to generate the PWM pulse train corresponding to a given signal is the intersective PWM: the signal (here the red sine wave) is compared with a sawtooth waveform (blue). When the latter is less than the former, the PWM signal (magenta) is in high state (1). Otherwise it is in the low state (0).

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The simplest way to generate a PWM signal is the intersective method, which requires only a or a waveform (easily generated using a simple ) and a. When the value of the reference signal (the red sine wave in figure 2) is more than the modulation waveform (blue), the PWM signal (magenta) is in the high state, otherwise it is in the low state. Main article: Direct torque control is a method used to control AC motors. It is closely related with the delta modulation (see above). Motor torque and magnetic flux are estimated and these are controlled to stay within their hysteresis bands by turning on new combination of the device's semiconductor switches each time either of the signal tries to deviate out of the band. Time proportioning Many digital circuits can generate PWM signals (e.g., many have PWM outputs). They normally use a that increments periodically (it is connected directly or indirectly to the of the circuit) and is reset at the end of every period of the PWM.

When the counter value is more than the reference value, the PWM output changes state from high to low (or low to high). This technique is referred to as time proportioning, particularly as time-proportioning control – which proportion of a fixed cycle time is spent in the high state. The incremented and periodically reset counter is the discrete version of the intersecting method's sawtooth. The analog comparator of the intersecting method becomes a simple integer comparison between the current counter value and the digital (possibly digitized) reference value. The duty cycle can only be varied in discrete steps, as a function of the counter resolution.

However, a high-resolution counter can provide quite satisfactory performance. Main article: PWM is also used in efficient.

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 and a. 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. Pulse-width modulation with 555 timers Many applications like electric fan motor speed controllers, and LED (or incandescent) lamp dimmers, we use the PWM concept. Here it is explained using the popular 555 timer: 555 timer is operated in monostable mode.

In this mode output is low till the input is applied, when triggering is applied to second pin of 555 timer IC output becomes high and it will be in high for some period of time. Time period is determined by T=1.1 RC where R is the resistor connected to 7th pin and C is the capacitance connected to 7th pin. Here the triggering input is applied to 2nd pin through differentiator circuit to get sharp pulses. The resistor of differentiator is connected to power supply so that to generate negative trigger pulses and diode is to avoid positive pulses. Here the output voltage is controlled using control pin IC. Whenever trigger pulse becomes low, the ouput of icswitches to high and as a result C keeps on charging until the voltage is above input voltage. Whenever the trigger pin is low output of IC switches to high and this process continues till the stream of pulses are obtained.

Audio effects and amplification PWM is sometimes used in sound (music) synthesis, in particular, as it gives a sound effect similar to chorus or slightly detuned oscillators played together. (In fact, PWM is equivalent to the difference of two with one of them inverted.) The ratio between the high and low level is typically modulated with a. In addition, varying the duty cycle of a pulse waveform in a subtractive-synthesis instrument creates useful timbral variations. Some synthesizers have a duty-cycle trimmer for their square-wave outputs, and that trimmer can be set by ear; the 50% point (true square wave) was distinctive, because even-numbered harmonics essentially disappear at 50%.

Pulse waves, usually 50%, 25%, and 12.5%, make up the. A new class of audio amplifiers based on the PWM principle is becoming popular. Called, they produce a PWM equivalent of the analog input signal which is fed to the via a suitable filter network to block the carrier and recover the original audio. These amplifiers are characterized by very good efficiency figures (≥ 90%) and compact size/light weight for large power outputs. For a few decades, industrial and military PWM amplifiers have been in common use, often for driving. Field-gradient coils in machines are driven by relatively high-power PWM amplifiers. Historically, a crude form of PWM has been used to play back digital sound on the, which is driven by only two voltage levels, typically 0 V and 5 V.

By carefully timing the duration of the pulses, and by relying on the speaker's physical filtering properties (limited frequency response, self-inductance, etc.) it was possible to obtain an approximate playback of mono PCM samples, although at a very low quality, and with greatly varying results between implementations. In more recent times, the sound encoding method was introduced, which uses a generalized form of pulse-width modulation called, at a high enough sampling rate (typically in the order of MHz) to cover the whole frequencies range with sufficient fidelity. Anthrax among the living album. This method is used in the format, and reproduction of the encoded audio signal is essentially similar to the method used in class-D amplifiers. Electrical SPWM (Sine–triangle pulse width modulation) signals are used in micro-inverter design (used in solar and wind power applications). These switching signals are fed to the that are used in the device. The device's efficiency depends on the harmonic content of the PWM signal.

There is much research on eliminating unwanted harmonics and improving the fundamental strength, some of which involves using a modified carrier signal instead of a classic sawtooth signal in order to decrease power losses and improve efficiency. Another common application is in robotics where PWM signals are used to control the speed of the robot by controlling the motors. See also. produces smooth behavior by way of discontinuous switching in systems. References.