PWM - What is it, How does it work and how to detect it.

[Cataract]

Great post. One question: is a circuit that supports higher frequency PWM more expensive to manufacture? Wondering why anybody would go with the lower frequency variety except maybe for cost reasons.

In general, higher frequency circuits are more expensive, so I would tend to say that is the reason for the tendency to use lower frequency circuits.

Some years ago i read that low frequency is more efficient. So i guess thats why. Dont know for sure, so dont quote me on that ;-)

I wouldn't quote myself either, but I think you're right, especially when it comes to a circuit that can drive an LED with higher amps.

 

[Jvvjvv]

I too would like to thank you for all the work you put into this thread. I too was unaware of PWM. It made me wonder that, if the differante way that the manufactures deliver the cycles, would cause a variance in battery drain?

 

[Cataract]

I too would like to thank you for all the work you put into this thread. I too was unaware of PWM. It made me wonder that, if the differante way that the manufactures deliver the cycles, would cause a variance in battery drain?

I am starting to really feel humbled by all the thanks. Thank you all for your feedback

The main goal of PWM is that it enables greater runtimes compared to constant current regulation. I have never really looked up the equations but, in theory, lower frequency PWM would mean longer runtimes since faster clocks generally need more energy. The difference in runtime VS PWM frequency might be fairly small and better quality chips can easily compensate for the difference in battery drain when using higher frequency PWM. The quality comes with a price as it does for everything else in life, though.

 

[xzel87]

I'm not sure how effective it is at various frequencies, but I can clearly see the PWM on my Lumintop Tool AAA on medium and low when I try to take a picture of the beam with my smartphone (HTC M7).It kinda appears as scan lines in the pic. Dropbox link below if anyone's interested.

https://www.dropbox.com/s/jp71zvwfzxsz7go/IMAG2661.jpg?dl=0

And, much thanks for the in depth information cataract.

 

[Mr. Nobody]

Is it possible for our brains or eyes to see PWM ? For example if I were watch a two people toss a football I am able to slow it down and perceive it as slow moving pictures. (Does that example make sense ?) Either I am weird or have a medical condition...either way I have lived with this for years and see a benefit.

This includes any moving object not just a football.

 

[RI Chevy]

Yes. We can see lights that have or use PWM.

 

[reppans]

The main goal of PWM is that it enables greater runtimes compared to constant current regulation. I have never really looked up the equations but, in theory, lower frequency PWM would mean longer runtimes since faster clocks generally need more energy. The difference in runtime VS PWM frequency might be fairly small and better quality chips can easily compensate for the difference in battery drain when using higher frequency PWM. The quality comes with a price as it does for everything else in life, though.

Interesting, HKJ mentioned that current regulated lights should be more efficient. However, I do output/runtime tests on the sub-/low- lumen modes I use most often and find it all over the map... so - clear as mud .

http://lygte-info.dk/info/DriverTypes UK.html

 

[scs]

Pwm bothers me when its frequency is low enough that I can detect it by waving my hand very rapidly in front of the light ,and my hand appears to fan out like a deck of cards in hand.

 

[Cataract]

Interesting, HKJ mentioned that current regulated lights should be more efficient. However, I do output/runtime tests on the sub-/low- lumen modes I use most often and find it all over the map... so - clear as mud .

http://lygte-info.dk/info/DriverTypes UK.html

Hmm... I might have been a little tired when I wrote that and failed to elaborate properly as it is possible to achieve longer runtimes with PWM under certain conditions. I prefer to keep things simple in this thread as it is intended to be easy to understand for everyone. Each has its advantages when it comes to runtime. For those who wish to study further, that link is an excellent read. Thanks for the link.

Pwm bothers me when its frequency is low enough that I can detect it by waving my hand very rapidly in front of the light ,and my hand appears to fan out like a deck of cards in hand.

I know exactly what you mean. I once tried to walk fast in an overgrown field while using a PWM headlamp. All the moving blades of grass looked like they multiplied and went slow-mo on me. ARGH!

 

[shanewang]

nice thread, really helpful for beginners like me

 

[jon_slider]

I recently started looking at single aaa lights and was interested in the Rev3 Maratac Cu, but am concerned about the PWM.. anyone care to comment whether they think the Maratac has good or bad PWM on any brightness setting?

here is my cheat sheet, hopefully accurate
==

includes hat clip, and No PWM


Olight i3s 20-85-0.50 lumens in mode sequence XP-G2
Thrunite Ti3 Aluminum 0.04-12-120 XP-G2
Thrunite Ti3 Stainless 0.04-12-120 XP-G2
Thrunite Ti3 Titanium 0.04-12-162 XP-L4 (Very floody and green compared to G2)


no hat clip, and No PWM
Fenix E05 2014 Aluminum 8-25-85 XP-E2 (more blue than G2)
Fenix E05 2014 Stainless 8-25-100 XP-E2
Fenix E05 2014 Titanium 4-27-100 XP-E2

===
===
Lighs with PWM and hat clip


Maratac Rev3, 40-1.5-138 XP-G2
ITP A3 1.5-18-80 XP-G2
===

 

[Flyingdrums]

Long time reader first time poster. I was on a search to put together my own PWM circuit for the high power LED light's that I build and finally settled on one based around the 555 timer (basically because I had all the components on hand). I hope to start a thread with it when I get my required posts because I try to include a little "light" hearted humor that hopefully people interested in this sort of thing can enjoy. Here is a link to the video that contains the circuit diagram used. No commercials, I promise.

 

[Cataract]

@ ion_slider: thanks for sharing that info.

@ Flyingdrums: That's a crazy build and gotta love that intro Your video would likely get better deserved attention in the homemade and modified flashlights section, though.

 

[RI Chevy]

Welcome to the forum! :welcome:

 

[Flyingdrums]

Thanks! I'll post it there when I get the all clear for starting a thread.

 

[Cataract]

You're only a few posts away....

Yea, I completely forgot :welcome:

 

[jon_slider]

another copper aaa light with PWM, but no hat clip is the Prometheus Beta, discussed here:
http://www.candlepowerforums.com/vb...-QR-LIVE-on-Kickstarter&p=4641643#post4641643

I notice the pwm. It's not bad but
I can notice it.

Same.

Im expecting delivery of a Rev3 maratac, will share my PWM impressions shortly.

 

[hbk_rey]

I like the copper AAA.

 

[jon_slider]

I have not been able to detect the PWM when using my recently arrived Maratac, unless I shine the light at a fan or running water. My phone camera does not pick it up. Im really liking the copper body. First impressions and pic links here http://www.candlepowerforums.com/vb/showthread.php?400559

 

[AHRS-24/7]

Thank you for this......good start for a new flashlight nerd.