I never really liked PWM signals being called digital.
Most pwm circuits operate in continuous time and there are no discrete pulse widths generated, they can be continously variable.

 

Perhaps, but they are definately more digital than analog. From what I'm hearing about microcontrollers they are becoming even more so.

 

Bill_M,

I haven't mentioned it yet but I think you deserve high praise for taking the time to compile this treatise on PWM. Next to LEDs and Microcontrollers, I think PWM is a frequent topic of post here in the forum.

http://forum.allaboutcircuits.com/attachment.php?attachmentid=15652&d=1264596237

In the post linked to above, you show a comparator with a potentiometer and several representative outputs. The two lower output plots are indicative of different settings of the potentimeter. I wonder if it would be a good idea to note on each, the setting of the potentiometer that yielded the output.


hgmjr

http://forum.allaboutcircuits.com/attachment.php?attachmentid=15652&d=1264596237

 

Bill_M,

Do you suppose anyone is going to quibble over the fact that the two high-side MOSFET devices in your H-bridge (in the motor driver illustration) requires a high-side driver to switch properly?

hgmjr

P.S. This is not a quibble.

 

I think it would be helpful if the diagram showing the sinusoid to PWM waveform would benefit from being enlarged. This would provide greater resolution of the resulting PWM signal. I think it would make the concept clearer to those encountering PWM for the first time.

hgmjr

 

This picture does not appear correct to me.

If you create a path through the MOSFETs that drives a motor in one direction using a PWM signal, you do not want the reverse direction to be activated during the resting portion of the PWM.

 

From a grammatical persective, I think that the last sentence in the following paragraph.

Efficiency in this case is measured as wattage. If you have a SMPS with 90% efficiency, and it converts 12VDC to 5VDC at 10 Amps, the 12V side will be pulling approximately 4.6 Amps. The 10% (5 watts) not accounted for will show up as waste heat. While being slightly noisier, this type of regulator run much cooler than their linear counterparts.

may be better if altered to:

Efficiency in this case is measured as wattage. If you have a SMPS with 90% efficiency, and it converts 12VDC to 5VDC at 10 Amps, the 12V side will be pulling approximately 4.6 Amps. The 10% (5 watts) not accounted for will show up as waste heat. While being slightly noisier, this type of regulator runs much cooler than its linear counterparts.

I know, I know, now you can say I am being nit-picky.

hgmjr

 

This picture does not appear correct to me.

If you create a path through the MOSFETs that drives a motor in one direction using a PWM signal, you do not want the reverse direction to be activated during the resting portion of the PWM.

It is a bidirectional controller. If you have a 50% PWM signal, the motor will turn in neither direction, two directions being balanced. 0% is full rotation in one direction, and 100% is full rotation in the other direction. Motors, being basically inductive, will reject the high frequency components and respond to the low frequency component, much like speakers. It is simplified, but the base concept is valid.

You can drive a motor one way with one transistor, but for full control in both directions you need a H-Bridge.

 

Bill_M,

I haven't mentioned it yet but I think you deserve high praise for taking the time to compile this treatise on PWM. Next to LEDs and Microcontrollers, I think PWM is a frequent topic of post here in the forum.

http://forum.allaboutcircuits.com/attachment.php?attachmentid=15652&d=1264596237

In the post linked to above, you show a comparator with a potentiometer and several representative outputs. The two lower output plots are indicative of different settings of the potentimeter. I wonder if it would be a good idea to note on each, the setting of the potentiometer that yielded the output.


hgmjr

Actually the point I'm trying to make is the symmetry of the triangle wave doesn't matter. I lifted this image from a thread that is currently dormant.

I may have missed my mark a bit. They were originally separate, but I merged them trying to lay the flow of the article a bit smoother.

Perhaps a caption?

 

Bill_M,

Do you suppose anyone is going to quibble over the fact that the two high-side MOSFET devices in your H-bridge (in the motor driver illustration) requires a high-side driver to switch properly?

hgmjr

P.S. This is not a quibble.

Probably. If you have a better thought how to draw it, sketch it up as ugly as you like and I'll pretty it up. My thought is a 12 V power supply would do the job, top gets 0V, bottom gets 12V. Other side gets opposite.

I think it would be helpful if the diagram showing the sinusoid to PWM waveform would benefit from being enlarged. This would provide greater resolution of the resulting PWM signal. I think it would make the concept clearer to those encountering PWM for the first time.

hgmjr

I thought of that too. They keep drumming that they want to reduce the bandwidth, which left its mark. I'll redraw it and see if it looks better.

From a grammatical persective, I think that the last sentence in the following paragraph.



may be better if altered to:



I know, I know, now you can say I am being nit-picky.

hgmjr

Not a problem. This is the kind of feedback I'm hoping for.

 

OK, I redrew it twice, I remembered after the 1st there really was a width limit.

 

Bill_M,

Nicely done. That is very much improved.

hgmjr

 

I'm going to add captions to the pictures. If people like the wording (in other words, don't actively mention it) I'll merge it with the pictures before I pack the article.

I still have the second illustration to redraw, but I'm almost finished here.

 

OK, all the pictures have been touched up, and I think I've corrected most of my bloopers in the text.

I believe it is in the final proofreading phase.

Since I've been working on it all weekend I'm going to extend the time for packing for a full week.

 

Might mention that PWM has been commonly used in high power AM and Shortwave broadcasting since the early 1980s. It's functionality is not limited to solid state devices, the Harris MW-50, for example, is all vacuum tube ("hollow state") except for the low power PWM exciter.

Eric

 

I'm not familiar with that application. Are you referring to the power supplies of the units?

 

I'm reviewing the AAC book for any sections on PWM, and can't find anything. Anyone else see something I'm missing?[/QUOTE

I aded <section> </section> tags around the text. All else looked good

Thanks, Bill for your fine work.

for the record the new or updated files at ibiblio are :
dcdrive.sml contrib.sml 4300[34567].png 43003.png 43004.png 43005.png 43006.png 43007.png