Talk:Pulse-width modulation

Untitled

See also, Error Diffusion?

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I have the impression that this article is somewhat messy. applications, methods and principle are mixed together. Maybe we could organize this : principle (make the average value of a rectangular signal vary by modifying its duty cycle), applications (I'm a power electronics guy, so I only know applications in this field), methods to generate the pwm (like in the figure I added, but there are other)

What do you think?CyrilB 09:43, 24 March 2006 (UTC)

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I was looking for an information I have not get. Is the PWM used for both AC-DC converter and DC-AC inverter or just the latter one? I know it is not the proper place to ask this kind of questions. But it should be intereting that this article describe this point in the future.

-- -M-ric 02:44, 7 May 2006 (UTC)

PWM Controllers

This article needs to be extended especially voltage regulation section. PWM controller can be used in AC-DC as well as DC-DC conversion.I'll add some text in the voltage regulation and u can get some idea Kundojjala 17:32, 24 May 2006 (UTC)

Distributed PWM

Should we include distributed pulse width modulation, in which the pulse is broken up into a series of small pulses? This might not fall under pulse density modulation since a known duty cycle is output. Furthermore, there is no sigma-delta modulation going on. 128.151.161.49Iain (imarcuso@mail.rochester.edu)

Natural and Uniform Sampling?

There is no mention of natural and uniform sampling. A complete discussion of PWM would include these two different methods of implementing PWM (and information, perhaps, about the frequency-domain consequences). --TedPavlic | talk 18:35, 18 February 2008 (UTC)

Pulse Width Modulation vs Duty Cycle Modulation

The introductory statement is misleading: "Pulse-width modulation uses a square wave whose duty cycle is modulated". If you modulate the duty cycle (ie. freedom to move both the positive and negative edges, only ensuring that the ratio pulse width to pulse period matches the modulated signal) then you have duty cycle modulation. Pulse width modulation fixes one of the edges so you have a fixed period, and varies only the pulse width. The correct statement should be "Pulse-width modulation uses a square wave whose pulse width is modulated", but my change keeps getting reverted... —Preceding unsigned comment added by 129.215.215.162 (talk) 15:20, 1 April 2008 (UTC)

In my experience, a square wave is specifically a pulse with a 50% duty cycle; if you adjust the ratio of the time axis to the amplitude axis in a display or diagram, you can make each half cycle a square. I changed "square" to "pulse" throughout, because duty cycle varies. "Square" does not refer to the shape of the corners of the waveform! Including "rectangular" would be a good idea, but doing so increases verbal clutter. Perhaps my strong feeling is partially influenced by spending years with analog music synthesizers, in which a square wave definitely has a 50% dufy cycle. (You might want to remove the bit about setting 50% duty cycle by ear.) Regards, Nikevich (talk) 09:30, 26 July 2009 (UTC)

Try to use edit summaries, and mention that you'll be adding your reasoning to the talk page. As far as I could see, you were removing valuable context from the article with no clear explaination. Yngvarr (c) 15:22, 1 April 2008 (UTC)

This needs an mp3 sample

What's the point of learning about synths if you can't hear it? —Preceding unsigned comment added by 75.57.186.23 (talk) 20:41, 27 November 2008 (UTC)

Servos?

Almost all the servos I've seen are controlled by a PWM signal. Why is it, then, that this article doesn't even mention the word "servo" once? Salvar (talk) 14:01, 6 June 2009 (UTC)

Thats because most hobby servos are controlled by pulse position modulation, not pulse width modulation http://en.wikipedia.org/wiki/Pulse-position_modulation

97.65.61.9 (talk) 12:57, 27 October 2010 (UTC)

Afaik that is not true. Servos are controlled by PWM signals. Simpler DC motors translate PWM into voltage by their mechanical inertia acting as LPF. Modern servos have inner electronics, such that a certain pulse width and duty cycle PWM keeps them in the still position, a lower duty cycle causes rotation in one direction (with speed corresponding to the difference in duty cycle) while a higher duty cycle results in the other direction for rotation.

See Servo_motor , [1]. I've used a [2] servo and it also works on PWM. Hoemaco (talk) 17:12, 27 February 2011 (UTC)

Power Delivery

Should the line: "In this case the PWM duty cycle is defined by the frequency of the AC line voltage (50 Hz or 60 Hz depending on the country)" actually refer to period rather than duty cycle? —Preceding unsigned comment added by 134.225.210.40 (talk) 14:17, 3 July 2009 (UTC)

Class D amplifiers used in cell. phones?

I strongly suspect that PWM amplifiers are used for the earphone/speaker in a cell. phone, to economize on battery power. However, I'm not sure, so I didn't add such a comment. Nevertheless, if true (likely), this must be the most commonplace application of PWM technology.

Regards, Nikevich (talk) 09:38, 26 July 2009 (UTC)

Lamp dimmers at 2x power line frequency

They work on both half-cycles, unless I'm quite-badly misinformed. (Fairly sure a typical triac dimmer switches on at a variable point, and switches off when the load current comes close to zero.)

Regards, Nikevich (talk) 09:38, 26 July 2009 (UTC)

Deprecated title?

According to this source pulse-width modulation is deprecated terminology, preferring pulse-duration modulation. Does anyone know if this is officially deprecated and by whom? The term pulse-width was certainly standard in my day but pulse-duration certainly now seems to have growing popularity. SpinningSpark 16:53, 31 January 2011 (UTC)

inertial electrical devices

Inertial electrical devices; Explanation needed. I don't see an example of an inertial elecrical device in wiki. We should explain. I couldn't find anything. Could anyone help? Longinus876 (talk) 16:50, 1 September 2012 (UTC)

It's a simple concept, although I've not heard it described in this literal term before. It could certainly benefit from explanation.

PWM is applied to load device that have "inertia", either mechanical inertia such as a motor driving a flywheel, or thermal inertia such as a heating element housed in firebricks. This means that the time constant for their response (which depends on the ratio between the power of the motor or heater, vs. the inertia effects of the load) is longer than the pulse rate of the PWM signal. They thus respond slowly to the average of the PWM signal, rather than a fast response device (like a meter needle) that might flutter visibly through the PWM cycle time. Andy Dingley (talk) 18:41, 1 September 2012 (UTC)

Main Graphic demonstrating PWM

@Dicklyon:

In my opinion, the main graphic demonstrating PWM is dangerously vague. The sine wave is obvious, but its application to AC induction motors requires arguably advanced understanding of how AC induction motors work, and on its surface seems invalid.

I attempted to add a sentence explicitly confirming the validity of the graph in regards to ideal AC induction motors. However, my modification was reverted.

I would like to find a simple, concise way to give a hint to the reader regarding the validity of the graph as a description of an idealized AC induction motor.

Any suggestions?

I may take the time to attempt to simplify my proposed addition to the caption, in order to save others time who may also be confused - just to have something in there clarifying that this isn't a meaningless diagram specifically in relation to AC motors.

Daniel347x (talk) 21:07, 6 December 2014 (UTC)

Your addition to the caption read: Note that in this idealized plot, the current (and hence magnetic field) in the corresponding coil of the motor remain essentially constant when the voltage over the coil is zero (i.e., there is no significant energy drain); but this idealization is roughly correct if the switching frequency of the PWM is high enough. As an EE who knows a bit about magnetics, I still find this roughly uninterpretable in this context, as there's no info in the lead saying anything about the motor, or what the idealization is, or anything about energy transfer. I didn't understand how to interpret the "but" introducing the second part. In general, I think that as a clarification, this is a failure. I agree there's a problem. Probably it could be addressed better by making a section about motor control and moving the figure into it, so that some context for understanding the figure could be established. Dicklyon (talk) 22:38, 6 December 2014 (UTC)

How about: Note that the plot shown is idealized for the case of a motor that is drawing no power (so that the motor's internal magnetic fields remain constant when voltage is switched off during the PWM cycle).? — Preceding unsigned comment added by Daniel347x (talk • contribs) 22:55, 6 December 2014 (UTC)

I don't think that note is helpful in the context of a lead image that most people will not understand; it adds complexity without clarity. Make a section about motor control if you think more needs to be said. Dicklyon (talk) 01:47, 7 December 2014 (UTC)

I found the current caption confusing and lost time confirming that it was valid. If it is impossible to add anything to the caption to clarify the validity of the image, I suggest removing the image or replacing it with another. Do you think there is any addition to the caption that would satisfy both the need for clarity and the need for accuracy?— Preceding unsigned comment added by Daniel347x (talk • contribs) 02:55‎, 7 dec 2014 (UTC)

I think it's a poor choice of lead image; not fixable by saying more. Perhaps say less? Or replace it. Dicklyon (talk) 04:58, 7 December 2014 (UTC)

I like the idea of saying less. What is your opinion of this simplification of the caption: An example of PWM in an idealized inductor driven by a voltage source: the voltage source (blue) is modulated as a series of pulses that results in a sine-like current/flux (red) in the inductor. The smoothness of the resultant waveform can be controlled by the width (number) of modulated impulses (per given cycle).? — Preceding unsigned comment added by Daniel347x (talk • contribs) 05:03, 7 December 2014 (UTC)

Yes, that's better. For the sake of those who don't know about inductors and flux, mentioning that the red is the integral of the blue might be useful. I'd omit the last sentence. Dicklyon (talk) 05:27, 7 December 2014 (UTC)

I think the sentence regarding "smoothness of the resulting waveform" is key: A common instinct, I think, when first looking at this image, is to wonder how it's possible for a (blocky) square wave to emulate a smooth curve (sine wave). The key is the number of modulations per second. How about this: An example of PWM in an idealized inductor driven by a voltage source: the voltage source (blue) is modulated as a series of pulses that results in a sine-like current/flux (red) in the inductor. The blue rectangular pulses nonetheless result in a smoother and smoother red sine wave as the switching frequency increases. Note that the red waveform is the (definite) integral of the blue waveform. — Preceding unsigned comment added by Daniel347x (talk • contribs) 19:27, 7 December 2014 (UTC)

I'll go ahead and make the change. Please let me know if you have objections or further suggestions. Thanks!Daniel347x (talk) 19:43, 10 December 2014 (UTC)

I'm not clear exactly the change you made, but I like the way it reads now! Thanks! — Preceding unsigned comment added by Daniel347x (talk • contribs) 06:54, 13 October 2016 (UTC)

Carrier frequency?

I am confused about the use of the term "carrier frequency" in this section: "Pulses of various lengths (the information itself) will be sent at regular intervals (the carrier frequency of the modulation)." My understanding of the term "carrier frequency" is that it is the frequency at which a transmission is broadcast, e.g. tuning your radio dial to 88.5 MHz. The carrier frequency is typically much higher than the frequency of the frequency of the transmitted information. The regular intervals the article refers to seems to me to correspond more to a "pulse repetition frequency", or the inverse of the frame rate or update rate. I do not understand how the two concepts (frame rate and carrier frequency) are analogous or related. Jfalesi (talk) 02:58, 13 October 2016 (UTC)

MPPT and the term "PWM" as used by the solar industry

I noticed this quote in the PWM article:

"Along with maximum power point tracking (MPPT), it is one of the primary methods of reducing the output of solar panels to that which can be utilized by a battery.[1]"

It strikes me as problematic.

1) MPPT is not a method of reducing the output of solar panels. It is a method of maximizing power from a solar panel. MPPT charge controllers do have battery protection and sometimes multi-stage, programable charging options. However, these function and are implemented in similar ways as in "PWM" solar charge controllers. MPPT is not limited to use in battery charge controllers. It can also be used to match solar panels to other kinds of loads. I believe that in all cases it used, as the name suggests, to maximize power output from a solar panel.

2) The solar industry uses "PWM" to mean "not MPPT" in the context of battery charge controllers. So, PWM is used for controllers that do not use PWM at all, at least in the sense that PWM has to be modulated, eg. for systems based on Schmidt triggers, state machines, etc. And, MPPT is used for controllers that use do use PWM in their implementations.

All in all, I'm not sure that the sentence is helpful.

I haven't edited a Wikipedia page. So, I'm reluctant to just remove the MPPT sentence that I believe to be incorrect. Is this something that should be edited and if so what's the right way to do it?

Also, I'm not sure how useful or appropriate it would be to add a section discussing how PWM is used in relation to solar charge controllers.

NO mention of modern types of PWM ???

I did not find any section mentioning modern types od PWM e.g. "Selective Harmonic Elimination PWM" or "Space Vector Modulation" used everywhere in high power motors nowadays... 95.105.237.40 (talk) 08:53, 18 September 2022 (UTC)