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Building an LED light/flash
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mawyatt



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PostPosted: Tue Mar 10, 2020 10:38 am    Post subject: Reply with quote

Chris,

Agree that theory and hands on are the best approach, maybe not in that order tho Very Happy

Recall an incredibly complex system we were developing back in 80s, so advanced that we had to develop out own test equipment! We had created a new type clocking driver for some CCD chips we had developed, these chips were not imagers but real time mathematical convolvers that formed part of a Fourier Transform called "Chirped Z Transform". Our goal was to do spectral analysis, equivalent to 20,000 point 16 bit FFTs, plus a bunch of proprietary stuff, in real time. The equivalent computing power was 1/3 of Cray 1 Supercomputer but our system was the size of a small textbook and consumed 3 watts total!! The clock circuit was based upon a reactive clock scheme that utilized the CCD capacitance in resonance with an external inductance for energy exchange. This was all worked out theoretically and worked beautifully (much later (~10 years) the concept was patented by NASA, but we never brought prior art up since our sponsor was the USG, not a good idea to tick off the Wookey Rolling Eyes )

While doing some hands on measurements in the lab I knocked off one of the power supply wires, the system should have stopped but it didn't, and the total system power consumption dropped Shocked After checking everything out I went back to my desk and developed the theory behind what had just transpired. The reactive clock driver circuit was a unique circuit that forced itself into the lowest energy consumption, compensating for power supply and component variations, including temperature and even producing one of the supply voltages it required from the higher supply voltage. We kept this circuit as a Trade Secret until the NASA patent.

Anyway, that was a case where hands on preceeded some theory.

Todays chip design is almost totally based upon theory, since measurements with such small devices and features, as well as the amount of devices involved, prevents traditional hands on type experimentation. Even if you could make hands on measurements of a test board the results would be questionable since the parasitic elements in the chip and test board are so much different. Add to this the cost of a chip design and you can see why this is a highly specialized field where a mistake or inferior design can cost many Millions $. Very stressful indeed!!

Think about the work of James Maxwell, or Albert Einstein, or Issac Newton, they had no means to do hands on. Maxwell's 4 fundamental equations describing all EM phenomena, Einstein's Relativity & Gravitional Waves, Newtons laws, and so many more concrete contributions to human understanding, all done without any hands on....amazing indeed!!!


Best,
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chris_ma



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PostPosted: Tue Mar 10, 2020 12:35 pm    Post subject: Reply with quote

mawyatt wrote:
Think about the work of James Maxwell, or Albert Einstein, or Issac Newton, they had no means to do hands on. Maxwell's 4 fundamental equations describing all EM phenomena, Einstein's Relativity & Gravitional Waves, Newtons laws, and so many more concrete contributions to human understanding, all done without any hands on....amazing indeed!!!


hi Mike,

yes amazing indeed.

but from what I've heard, even something like Einsteins special theory of relativity originated from an experiment which indicated that the speed of light is the same towards the earths rotation as sideways to the rotation, which triggered the thought that the speed of light must be an absolute constant regardless of the observer, and Einstein followed that through with all it's crazy implications. I don't think he would have had this thought without the data from the experiments, so in a way even he needed hands on work.

in my eyes, one problem with todays physics is that the models are so accurate that there's rarely ever a miss match with the experiments, which means without any new contradicting hands on data it's very difficult to develop new models.

also I was talking more about engineering, not theoretical physics, and there even with the accurate theory behind other errors creep in from materials which is not to specs or things which interact in a very complex way, or that we have to live with limitations due to money constraints.

personally I'm somebody who enjoys thinking and designing way more then the actual building part, but I always found that at some point I simply have to start to make any meaningful advancements.
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mawyatt



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PostPosted: Tue Mar 10, 2020 1:10 pm    Post subject: Reply with quote

chris_ma wrote:
mawyatt wrote:
Think about the work of James Maxwell, or Albert Einstein, or Issac Newton, they had no means to do hands on. Maxwell's 4 fundamental equations describing all EM phenomena, Einstein's Relativity & Gravitional Waves, Newtons laws, and so many more concrete contributions to human understanding, all done without any hands on....amazing indeed!!!


hi Mike,

yes amazing indeed.

but from what I've heard, even something like Einsteins special theory of relativity originated from an experiment which indicated that the speed of light is the same towards the earths rotation as sideways to the rotation, which triggered the thought that the speed of light must be an absolute constant regardless of the observer, and Einstein followed that through with all it's crazy implications. I don't think he would have had this thought without the data from the experiments, so in a way even he needed hands on work.

in my eyes, one problem with todays physics is that the models are so accurate that there's rarely ever a miss match with the experiments, which means without any new contradicting hands on data it's very difficult to develop new models.

also I was talking more about engineering, not theoretical physics, and there even with the accurate theory behind other errors creep in from materials which is not to specs or things which interact in a very complex way, or that we have to live with limitations due to money constraints.

personally I'm somebody who enjoys thinking and designing way more then the actual building part, but I always found that at some point I simply have to start to make any meaningful advancements.


Chris,

I recall somewhere from long ago Einstein observed a slight curved effect on a building corner edge while riding a train which starting him thinking along those relativity paths. I think he even predicted gravitational lensing, which helped explain lots of things viewed in astronomy.

Long ago as a much younger man I got invited to a lecture by Dr Dirac on Unified Field Theory, I'll never forget that lecture. Way over my head, but just honored to be in the same room with him!!

There's still much uncertainty in designing chips. With today's chip density thermal becomes the ultimate limit and much work has been devoted to being able to accurately simulate not only the electronics but the effects of thermal. Some of the actual transistor device models now include a dual time constant thermal model to help with this problem.

Best,
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mjkzz



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PostPosted: Tue Mar 10, 2020 3:07 pm    Post subject: Reply with quote

Mike,

OK, this has successfully interrupted my train of thought coding Very Happy Now, I think I am going to enjoy this entertainment, too Very Happy

First, since you have accused me being wrong about "infinity" thing, OK, sure from physics point of view, yeah, there are current flowing through a diode before it is called "on", but compared to the current flowing though at or after it is ON, the difference is substantial enough to be considered as change of state. If I remember it correctly, there are two TYPICAL voltages, 0.7V and 0.3V, actual value depends on actual SPECIFIC device and how it is made. 0.7V and 0.3V are the generally accepted values.

With this change of state, "conducting" and "non-conducting", and if you look at a voltage-vs-current chart, you will see as voltage increases, the current goes up pretty steeply, and when voltage goes too far, the line is almost vertical, suggesting what you have in mind -- 59mV can cause substantial change of current.

THIS ACTUALLY IS THE BASE of my suggestion that you can not use it on all LEDs and I kept calling out for the LED model you used in your "circuit".

I will leave it here so we do not have quote stuff over and over with multiple points to discuss. Next post will be about how to model a modren LED.
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mjkzz



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PostPosted: Tue Mar 10, 2020 3:27 pm    Post subject: Reply with quote

Next (so we can keep track of things).

What is your simulation model with your "circuit" for the load? And this is the critical part for all other accusation Very Happy

If you have a COB LED, go through the exercise I mentioned, plot a chart with voltage and current on it. After you finish that, you will see that graph is VERY DIFFERENT from a typical chart for diode and this is the base I mentioned before, you will see the 59mV thing is NOT applicable at all, you do not have a line for current going up as steep as a diode would. Sure you might observe some similar behavior, but in the operating region of it, it is NOT the same, far (fetched) from it. Modern LEDs are made to emit more light than being a perfect diode. So from experiment, hands-on experience, one would not model a modern LED as a diode. I can have a power supply with 200mV ripple and still not having flikering.

Like I said before, all the stuff you throw out are common knowledge and are well understood by even high school kids. Is the 59mV theory (not yours, I will explain what "yours" is, I think you mis-interpret it or I did not make it clear Very Happy). or what you called Schottky prediction wrong? NO. It is how you apply that. Can you really apply it to a device that has a voltage-current chart so different from a diode? NO.

Of course, all this are based on one fact -- actual plot of voltage-vs-current chart of a modern LED
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mjkzz



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PostPosted: Tue Mar 10, 2020 3:32 pm    Post subject: Reply with quote

OK, this is clarification of "your theory" about the 59mV observation. Let me make it clear: I was referring to the fact that you suggested it in the discussion, something you think might help solving different observations, ie, something you theorized. You know, in many discussion, someone comes in with a suggestion, or an idea, we normally refer that as his/her theory? It is in that sense. So later on, I have changed it to "your idea" or Mike's idea. I did not mean the theory or discovery is yours, really. Hope this is clear.
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mjkzz



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PostPosted: Tue Mar 10, 2020 3:50 pm    Post subject: Reply with quote

Now, OK you got me (again vs infinity current change thing), a diode is a diode, is a diode. Sure perfect, agreed.

Again, like I said before, if you plot a V-vs-I chart for a modern LED, you will see the chart is substantially different from a diode within operating region spec'ed by LED manufacturer. Is it still a diode? Maybe from physics sense

So, from practical point of view, can you really use a model for diode in your circuit? This is why I kept calling you out about how you modeled your load for your "circuit". Had you given me that, I think all of these discussion will not be necessary because I re-read your 59mV idea and realized you are not one of those stubborn people who insist on using CC circuit to drive a high powered LED for high speed video application. And when I present my circuit to them, without an expensive, high performance CC circuit (and no, no large caps, either), they are shocked by how well it works, no flickering at all at 1000fps (I have not tried at 5000 fps yet, waiting to get it).
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PostPosted: Tue Mar 10, 2020 3:59 pm    Post subject: Reply with quote

So, in summary, like I said before, all the stuff, theories, etc you quoted, referenced are sound common knowledge, and I am surprised that you haven't quoted Einstein yet, just kidding. It is when you apply them and how you apply them within the region the device is used.

Again (and again), PLEASE get a modern LED, plot that chart, compare it with a diode, and see if you can still treat it as a diode. You do not have that steep, almost vertical, line going up, WITHIN specification of LED maker, ie, within the operating region that an LED is supposedly used. Since the chart is much more moderate, even a 200mV ripple on a 12V or 24V power supply would not cause flickering.
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PostPosted: Tue Mar 10, 2020 4:02 pm    Post subject: Reply with quote

Finally, I think I know why viktor got different result. I am calling you out for an answer. If you do not trust me, we can get someone here and send answers to that person.
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mawyatt



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PostPosted: Tue Mar 10, 2020 4:48 pm    Post subject: Reply with quote

mjkzz wrote:


THIS ACTUALLY IS THE BASE of my suggestion that you can not use it on all LEDs and I kept calling out for the LED model you used in your "circuit".



Peter,

If the "circuit" you reference is the "Fast LED Strobe for Macro" thread

https://www.photomacrography.net/forum/viewtopic.php?t=40999

This is current mode control and the LED characteristics don't matter since the current is forced thru the LED regardless of the LED parameters (within reason). This circuit is so immune to the load that you could put a LED, resistor, diode string, even a battery, or some combination of these and the load current wouldn't change unless the current source compliance voltage was exceeded. This is the benefit of negative feedback constant current mode operation. The model used in the simulation was just an ideal zener diode of the proper voltage and a resistor.

Best,
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mjkzz



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PostPosted: Tue Mar 10, 2020 5:02 pm    Post subject: Reply with quote

mawyatt wrote:
mjkzz wrote:


THIS ACTUALLY IS THE BASE of my suggestion that you can not use it on all LEDs and I kept calling out for the LED model you used in your "circuit".



Peter,

If the "circuit" you reference is the "Fast LED Strobe for Macro" thread

https://www.photomacrography.net/forum/viewtopic.php?t=40999

This is current mode control and the LED characteristics don't matter since the current is forced thru the LED regardless of the LED parameters (within reason). This circuit is so immune to the load that you could put a LED, resistor, diode string, even a battery, or some combination of these and the load current wouldn't change unless the current source compliance voltage was exceeded. This is the benefit of negative feedback constant current mode operation. The model used in the simulation was just an ideal zener diode of the proper voltage and a resistor.

Best,


sure, I know this kind of circuit, I think we discussed this type of thing before, feedback.

I am not accusing that you are wrong, but when you design something to drive an LED, don't you think it is a good idea to put an LED model as load? No, no, nothing wrong with what you did, but like your signature says, you never know what you will find :-)
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PostPosted: Tue Mar 10, 2020 5:05 pm    Post subject: Reply with quote

Also, those scope captures, are they real thing with your tektroinic scope, if so, I really need something like it, the portable one is getting too limiting.
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mawyatt



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PostPosted: Tue Mar 10, 2020 6:22 pm    Post subject: Reply with quote

mjkzz wrote:
Next (so we can keep track of things).

What is your simulation model with your "circuit" for the load? And this is the critical part for all other accusation Very Happy

If you have a COB LED, go through the exercise I mentioned, plot a chart with voltage and current on it. After you finish that, you will see that graph is VERY DIFFERENT from a typical chart for diode and this is the base I mentioned before, you will see the 59mV thing is NOT applicable at all, you do not have a line for current going up as steep as a diode would. Sure you might observe some similar behavior, but in the operating region of it, it is NOT the same, far (fetched) from it. Modern LEDs are made to emit more light than being a perfect diode. So from experiment, hands-on experience, one would not model a modern LED as a diode. I can have a power supply with 200mV ripple and still not having flikering.

Like I said before, all the stuff you throw out are common knowledge and are well understood by even high school kids. Is the 59mV theory (not yours, I will explain what "yours" is, I think you mis-interpret it or I did not make it clear Very Happy). or what you called Schottky prediction wrong? NO. It is how you apply that. Can you really apply it to a device that has a voltage-current chart so different from a diode? NO.

Of course, all this are based on one fact -- actual plot of voltage-vs-current chart of a modern LED


Peter,

Do you even read the references or what I've said!! Think you are getting mixed up again, it's not Schottky as you've stated above, but William Shockley, the co-inventor of the bipolar transistor at Bell Labs in 1947. The equation that describes diode behavior is the Shockley Diode Equation.

Agree, you can't apply Schottky but yes you can apply the Shockley Equation as has been stated and referenced before, an LED is a DIODE!

Please remember COB LEDs and LEDs are not the same, please reread my post about what a COB is!!

The 59mv theory you seemed obsessed with is derived from the Shockley Diode Equation, this equation describes an ideal diode characteristics with a ideality factor of 1 and without any series resistance. LEDs are also diodes and they have series resistance.

From:
https://ecee.colorado.edu/~bart/book/book/chapter4/ch4_4.htm

4.4.4. I-V characteristics of real p-n diodes

Next Subsection
First, there is the ideal diode region where the current increases by one order of magnitude as the voltage is increased by 60 mV. This region is referred to as having an ideality factor, n, of one.



From:
http://www.eng.auburn.edu/~niuguof/2210labdev/html/diode.html

An ideal diode has the following Shockley I-V characteristics:


the voltage difference corresponding to 10x current difference is 60 mV theoretically for ideal diodes. Higher order physical effects degrade the I-V slope. As a result, it takes more than 60 mV voltage increase to increase the current by one decade, or 10x.

near room temperature we can deduce the 60 mV per decade rule, which says that Vf increases approximately 60 mV for every factor of 10 increase in Id


BTW we are all anxiously waiting for you to provide a reliable reference that indicates an LED is NOT a diode, even a reference that doesn't call it a diode or pn junction!!

Best,
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mawyatt



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PostPosted: Tue Mar 10, 2020 6:44 pm    Post subject: Reply with quote

mjkzz wrote:
mawyatt wrote:
mjkzz wrote:


THIS ACTUALLY IS THE BASE of my suggestion that you can not use it on all LEDs and I kept calling out for the LED model you used in your "circuit".



Peter,

If the "circuit" you reference is the "Fast LED Strobe for Macro" thread

https://www.photomacrography.net/forum/viewtopic.php?t=40999

This is current mode control and the LED characteristics don't matter since the current is forced thru the LED regardless of the LED parameters (within reason). This circuit is so immune to the load that you could put a LED, resistor, diode string, even a battery, or some combination of these and the load current wouldn't change unless the current source compliance voltage was exceeded. This is the benefit of negative feedback constant current mode operation. The model used in the simulation was just an ideal zener diode of the proper voltage and a resistor.

Best,


sure, I know this kind of circuit, I think we discussed this type of thing before, feedback.

I am not accusing that you are wrong, but when you design something to drive an LED, don't you think it is a good idea to put an LED model as load? No, no, nothing wrong with what you did, but like your signature says, you never know what you will find :-)


Since you claim to "know this kind of circuit", care to give us a detailed analysis of how it works?? Why many of the load characteristics don't matter.

Best,
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mawyatt



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PostPosted: Tue Mar 10, 2020 6:51 pm    Post subject: Reply with quote

mjkzz wrote:
Also, those scope captures, are they real thing with your tektroinic scope, if so, I really need something like it, the portable one is getting too limiting.


Not sure what scope captures you are referring to, but the 2 identical scopes shown in the image are Tektronix 2465 analog scopes. These are from the ~1985 era, and purely analog.

Best,
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