John Curl's Blowtorch preamplifier part II

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That's illuminating <ducks>.

The first time I have seen an absolute maximum reverse current spec. One wonders if that is a degradation mechanism similar to the effect of reverse breakdown on base-emitter junctions, which is well-known to degrade beta.

In that other forum years ago a couple of us took issue with the operation of a very sensitive soul's "optical compressor" as being questionable, as the guy had a 100nF driving the LED of an optocoupler --- and nothing else. PRR stepped in and chided us for our failure to see that the designer was counting on the reverse breakdown of the LED to pass currents of both polarities. Indeed that was how it managed to work, but I maintained that the breakdown voltage was not an even-remotely-guaranteed spec. I even measured a bunch of LEDs, and contacted the manufacturer of the opto about it, receiving a stony silence.

So maybe the design was something that needed an extended "break-in" :rolleyes:

But so far, all of this data about light output aging has not touched on the association, or perhaps the lack of it, with forward-biased I-V curves and noise. I haven't looked too hard, but searches for such are not yielding much of anything.

There was a paper I saw some time ago that showed photomicrographs of lit leds as they aged, there were thin straight lines of dark that appeared as they aged, many 60 degrees to each other so related to lattice defects perhaps?
 
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There was a paper I saw some time ago that showed photomicrographs of lit leds as they aged, there were thin straight lines of dark that appeared as they aged, many 60 degrees to each other so related to lattice defects perhaps?
Most interesting. If that reference turns up it would be fun to read.

Ceramic caps have a very strong power law for degradation as a function of voltage, and it wouldn't be surprising if some semiconductor degradation had comparable laws. The one paper had a sort of Arrhenius exponential equation but this is often applied when people can't think of anything else.

I'm busy but tempted to run some noise and forward voltage measurements on a few LEDs and really beat them up in an attempt at accelerating aging. But one can easily go too far. It reminds me of the old gag about fabricating LEDs and DEDs (dark emitting diodes) on the same wafer, and being assured of 100% yields.
 
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The generic red LED's seem quiet enough and I usually stick a couple hundred Ohms and a cap after them. At about 1.7 Volts with a BE junction you get 1 Volt across the emitter resistor keeping the math within my capabilities. The white ones these days for lighting have hour limits but they are pushed hard and do drop off in lumens over time. Just a curiosity question because some of these have been in the field for 20 years and still going.
 
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I have someone who continues if given the chance to say he rejected LEDs as biasing sources because of the photosensitivity.

Yes, there is a little, especially for the reds and to some extent the greens. But it is a tiny effect as far as current goes compared to a healthy forward bias.

I just did a quick check on a series string of four HLMP-6000 parts. I ran 50mA through them and looked at the voltage with a JFET gain of 30 preamp. The preamp lifts me out of Ap noise, but the LEDs are so small an uncorrelated addition to the preamp noise (about 881pV/sq rt Hz) that I can not reliably measure the LED noise, which should be twice the density of a single one. The rough estimate is 250pV/sq rt Hz for each LED.
 
My kidneys took a hit, so I get tested for function every 6 months. Did get a specialist consult who basically said unless below 10% functioning not an issue for her. ( I think I have mentioned my left leg is the only major body part that is still all OEM.)

Also very important the type of test used. Common US tests (creatinine level) make assumptions about your diet. The Brits use a test (GFR glomerular filtration rate) that takes longer but is more accurate.

My function would be just great for someone who only had one kidney.
Last week at speedskating practice, I asked one of the 4 member doctors a question about my medications. So that I would have more info when I see my primary care physician. See pointed out that the creatinine range standards probably don't apply to my type of body (small, muscular and old) So I looked on the internet and never found anything on the range, but I did find 4 things that impact the test.

1] Eating meat
2] Caffeine
3] Strenuous exercise
4] Dehydration

************************
On another note. At the World Championship Track Meet last month. A Bronze Medalist hurdler was to receive a kidney transplant (from his sister) the next week.
 
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Maybe, but all solid state devices have some photovoltaic properties.
In my (granted....very limited) experience they work better than any
other within reason alternative.
And you can put tubing over them, or otherwise keep them in the dark. But for everyday light levels it's a matter of perhaps a nanoamp compared to milliamps, so I don't worry about it most of the time.

I did an infrasonic filter design for a voice-coil temperature measurement system and prototyped it. I had 1N4148s as clamps in the input stage. The impedances were high enough that their light sensitivity was a problem for the board when tested on the bench. I changed them out for diode-connected opaque-case JFETs and the problem was eliminated.
 
Last week at speedskating practice, I asked one of the 4 member doctors a question about my medications. So that I would have more info when I see my primary care physician. See pointed out that the creatinine range standards probably don't apply to my type of body (small, muscular and old) So I looked on the internet and never found anything on the range, but I did find 4 things that impact the test.

1] Eating meat
2] Caffeine
3] Strenuous exercise
4] Dehydration

************************
On another note. At the World Championship Track Meet last month. A Bronze Medalist hurdler was to receive a kidney transplant (from his sister) the next week.

One other factor is race. When I took the hit my kidneys were a bit unhappy and the creatinine levels started at the needs new one levels and over the course of a week dropped enough they let me go home. Expectation was the level would drop to normal. Never quite got back there.

But much thanks for the comments.
 
I have someone who continues if given the chance to say he rejected LEDs as biasing sources because of the photosensitivity.

Yes, there is a little, especially for the reds and to some extent the greens. But it is a tiny effect as far as current goes compared to a healthy forward bias.

I just did a quick check on a series string of four HLMP-6000 parts. I ran 50mA through them and looked at the voltage with a JFET gain of 30 preamp. The preamp lifts me out of Ap noise, but the LEDs are so small an uncorrelated addition to the preamp noise (about 881pV/sq rt Hz) that I can not reliably measure the LED noise, which should be twice the density of a single one. The rough estimate is 250pV/sq rt Hz for each LED.

If it is going to matter, this gives me an excuse to use my new low noise preamp. Just let me know.
 
A question for one and all, personal views welcome.

I am nearing the end of the amp I have worked on for quite some time. It is expected to deliver 28.3Vrms into 8 and 4 Ohma, and as much of it as possible into 3 Ohms, in all cases into pure resistive loads, anto load paralleled with 1 uF and load paralleled into 2 uF. It's a fully complemetary design, using a three stage drive, predriver, driver and 4 pairs of NJW 200W output devices. No wimp, to be sure.

The PSU is divided into a central PSU, using 4*10,000 uF per psu line, separate for both sides. Further, each output device and the driver will have additional 2,200uF caps as near to them as possible. Each side will have twin full wave bridge recitifiers.

So, the question is: by type, I will use custom wound toridal transformers, but how should I size them? 500VA? 600VA? Their reglation is small at just 3% for sizes from 500VA upwarda, and I can go stark raving mad up to 3,000VA. in steps: 300, 400, 500, 600, 800, 1,000, 1,500, 2,000 and 3,000VA. What would you do in my place?
 
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