Induced Voltage
- Thread starter jbond
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SAC
Senior Member
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- Massachusetts
An LED's typical forward voltage is the voltage that the LED will be at for its typical rated current - that which gives the typical rated luminance. There were at least 7000 LEDs with a typical forward voltage of 2 volts or greater.
Your comment is somewhat puzzling to me given that you previously stated "Not many LED's light up very good at 2 volts". An LED with a typical forward voltage of less than 2v will generally "light up pretty good" at less than 2v. Digikey lists about 1500 LEDs that will generally "light up pretty good" at less than 2v.
gar
Senior Member
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- Ann Arbor, Michigan
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- EE
090314-1801 EST
physis:
I did not say I could see light at 0.1 microamp. However, I just now did a test on the 5366 and between 0.5 and 0.8 microamp there is detectable light. The input power at this level is about 1.4*0.5*10^-6 or 0.7 microwatt. Note: this LED has a narrow beam.
I believe the E on the left of the part number is for the highest output units.
See p21 for Intensity Ranking. For EFR and 20 MA it is listed as a minimum of 3600.
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physis:
I did not say I could see light at 0.1 microamp. However, I just now did a test on the 5366 and between 0.5 and 0.8 microamp there is detectable light. The input power at this level is about 1.4*0.5*10^-6 or 0.7 microwatt. Note: this LED has a narrow beam.
I believe the E on the left of the part number is for the highest output units.
See p21 for Intensity Ranking. For EFR and 20 MA it is listed as a minimum of 3600.
.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
090314-1940 EST
I have now created a 120 V pilot light with the 5366 LED, a reverse biased 1N4148, and two 100K 1/4 W resistors in series.
This provides adequate light for some purposes, maybe not direct sunlight.
Added two 0.01 mfd capacitors in series in this series string, but actually one was an 0.001 mfd that was in the wrong box. So actually it was about 0.001 mfd in series. This produced noticeable light.
Now let's see if a 5000 ohms shunt solves jbond's problem.
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I have now created a 120 V pilot light with the 5366 LED, a reverse biased 1N4148, and two 100K 1/4 W resistors in series.
This provides adequate light for some purposes, maybe not direct sunlight.
Added two 0.01 mfd capacitors in series in this series string, but actually one was an 0.001 mfd that was in the wrong box. So actually it was about 0.001 mfd in series. This produced noticeable light.
Now let's see if a 5000 ohms shunt solves jbond's problem.
.
ohmhead
Senior Member
- Location
- ORLANDO FLA
history of leds
history of leds
well long before leds were made that old transistor if ya cut the top off and looked down on the npn junction you could see lite they kinda found out how to manufacture leds when that became known i always thought a led dropped 2 volts to get np junction to conduct ?comments Best to yas nice posts please dont stop
history of leds
well long before leds were made that old transistor if ya cut the top off and looked down on the npn junction you could see lite they kinda found out how to manufacture leds when that became known i always thought a led dropped 2 volts to get np junction to conduct ?comments Best to yas nice posts please dont stop
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
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- Electrical Contractor
I've also read that most transistors are photo-sensitive.
physis
Senior Member
Dump the series capacitance, you'll actually do much better.
I'd almost guarranty it. But the resistance should be calculated for whatever the stray current is, and then doubled, or should I say halved. I mean to double the current sinking.
How is a diode reverse biased on AC? I can't imagine you're backwards feeding the LED and still getting light from 360 uAmps.
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physis
Senior Member
I thought I'd mentioned this but I don't see it so I guess I didn't.
What are most photo-electric gizmos made from?
ohmhead
Senior Member
- Location
- ORLANDO FLA
Well yes i think the old type of microcontroller chips.
When you programed these and wanted to erase you program out of that chip you took a ultra violet blue light ran it across the top of the micro chip and program was erased then also a program on some older micro chips were a one time deal once programed it was in stone get a new chip if you made a mistake programing it . Today its nice you can program a chip and erase 1000 times you can edit and change it add to the program and do it while its in circuit .But i dont know that much about it iam just a simple electrician and i like playing around making electronic tools for the trade its kinda a hobbie now check out my web site JENCORE.NET . Take care best to yas
When you programed these and wanted to erase you program out of that chip you took a ultra violet blue light ran it across the top of the micro chip and program was erased then also a program on some older micro chips were a one time deal once programed it was in stone get a new chip if you made a mistake programing it . Today its nice you can program a chip and erase 1000 times you can edit and change it add to the program and do it while its in circuit .But i dont know that much about it iam just a simple electrician and i like playing around making electronic tools for the trade its kinda a hobbie now check out my web site JENCORE.NET . Take care best to yas
physis
Senior Member
EPROM's isn't quite what I was getting at. I was pointing to silicon.
ohmhead
Senior Member
- Location
- ORLANDO FLA
Phonons
Phonons
Well you are most correct in you thinking ,
Its called energy to pass thur a silicon material in diodes or transistors same effect ,heres why both energy and momentum the flow of electrons thur silicon is a indirect band gap material electrons in the conduction band the energy given up in passin thur this conduction band to the valance band or outer shell ends up as visible light PHONONS . In simple electricians terms meaning it heats up that crystal lattice structure and emits light we see . Is this what SILICON does= [yes] freq will effect color also !! best to yas
Phonons
Well you are most correct in you thinking ,
Its called energy to pass thur a silicon material in diodes or transistors same effect ,heres why both energy and momentum the flow of electrons thur silicon is a indirect band gap material electrons in the conduction band the energy given up in passin thur this conduction band to the valance band or outer shell ends up as visible light PHONONS . In simple electricians terms meaning it heats up that crystal lattice structure and emits light we see . Is this what SILICON does= [yes] freq will effect color also !! best to yas
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gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
090315-0912 EST
physis:
The parallel circuit of an LED and reverse biased diode, then in series with a resistor, and capacitor was to provide an equivalent circuit for the problem of the original post. The capacitance is the coupling capacitance between wires in the cable.
The series resistance is what is required to limit the LED current for whatever operating voltage will be applied to the pilot light assembly.
For the problem of the original post the shunt resistance across the pilot light assembly that I suggested has to be a value low enough to lower the voltage to the pilot light assembly sufficiently so no appreciable light is emitted. My guess at 5 K may or may not be low enough. One could also use a shunt capacitor, or at the input to the wire going to the pilot light use a SPDT contact and switch between a hot line and neutral (ground) instead of floating the wire to the LED.
The reverse biased diode is in parallel with the LED and it being back biased is in reference to the LED. This is one way to prevent a high inverse voltage on the LED. The PIV rating for the Stanley I referenced above is 5 V, but also note I experimental took this to 27 V and saw negligible current flow. At some point there will be breakdown and this is obviously not controlled like it is in a Zener diode. The higher the breakdown point the higher the dissipation when it breaks down. Other means are to use two LEDs back to back, use a bridge rectifier, or a voltage divider that limits PIV.
.
physis:
The parallel circuit of an LED and reverse biased diode, then in series with a resistor, and capacitor was to provide an equivalent circuit for the problem of the original post. The capacitance is the coupling capacitance between wires in the cable.
The series resistance is what is required to limit the LED current for whatever operating voltage will be applied to the pilot light assembly.
For the problem of the original post the shunt resistance across the pilot light assembly that I suggested has to be a value low enough to lower the voltage to the pilot light assembly sufficiently so no appreciable light is emitted. My guess at 5 K may or may not be low enough. One could also use a shunt capacitor, or at the input to the wire going to the pilot light use a SPDT contact and switch between a hot line and neutral (ground) instead of floating the wire to the LED.
The reverse biased diode is in parallel with the LED and it being back biased is in reference to the LED. This is one way to prevent a high inverse voltage on the LED. The PIV rating for the Stanley I referenced above is 5 V, but also note I experimental took this to 27 V and saw negligible current flow. At some point there will be breakdown and this is obviously not controlled like it is in a Zener diode. The higher the breakdown point the higher the dissipation when it breaks down. Other means are to use two LEDs back to back, use a bridge rectifier, or a voltage divider that limits PIV.
.
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glene77is
Senior Member
- Location
- Memphis, TN
Gar,
I hate to say that it was 30 years ago, circa 1982.
But, it was low.
These were early LED's, very dim at 15 mA, as I recall.
I still have some, but am not setup to check it right now.
I really appreciate the currency of your experimental measurements.
Makes me want to clean up, set up more of my old gear. :smile:
I did a lot of instrumentation development. Analog IC design.
glene77is
Senior Member
- Location
- Memphis, TN
You can get forward "current" with an applied voltage of about .6.
Since the LED is a diode,
you can get measurable forward current on a Log scale
with applied voltages down to next to nothing.
I worked with non-linear amplifiers and diodes/LEDs
in negative feedback circuits when I was younger. Fascinating.
Impurities will be a limiting problem, introducing series resistance, etc.
Anyway, at very low current levels, they don't light-up enough to be useful. Only when the forward voltage is above the breakover around 1.8V, depending on the brand and model.
glene77is
Senior Member
- Location
- Memphis, TN
Gar
"LEDs back to back"
Are suggesting diodes in parallel, one heading west and one heading east ?
-|<-
->|-
Aside,
For myographic signals (bipolar signals like AC sine wave),
combined with resistors/caps, used in multiple,
this was typical of my prototyped negative feedback loops.
It was very temp sensitive, but the prototype was quick.
Next level was to use grounded base transistors, in groups,
with resistors and caps and bias introduced.
I bet that makes sense to you. :smile:
"LEDs back to back"
Are suggesting diodes in parallel, one heading west and one heading east ?
-|<-
->|-
Aside,
For myographic signals (bipolar signals like AC sine wave),
combined with resistors/caps, used in multiple,
this was typical of my prototyped negative feedback loops.
It was very temp sensitive, but the prototype was quick.
Next level was to use grounded base transistors, in groups,
with resistors and caps and bias introduced.
I bet that makes sense to you. :smile:
glene77is
Senior Member
- Location
- Memphis, TN
Gar,
Here is a circuit with what I mean by paralleled diodes.
Here is a circuit with what I mean by paralleled diodes.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
090315-1711 EST
glene77is:
If the LEDs are back to back we get twice the light output but a packaging problem compared to a diode with one LED. I do not know if anyone manufactures an LED package with a back to back pair of LEDs. The bridge rectifier method requires four diodes instead of one. All of this you know but maybe this will help others understand what has to be done in this type of circuit.
Somewhere I have some LEDs from the late 60s and sometime I will check their sensitivity.
From Wikepedia:
Any LEDs that I used prior to 1970 would not have cost more than about $1 each. By about 1972 or 1973 I started using 7 segment LED displays. Just prior to this I used displays with small incandescent lamps for each segment. It was not until the late 60s, maybe 67 or 68, that I could afford to experiment with RTL integrated circuits.
I believe in a previous post you described the development of a wide dynamic range log amplifier. To what use did you apply this? I believe in the 30s or 40s Ballantine or similar company manufactured a log AC voltmeter with vacuum tubes. Do you know what their design philosophy was?
This seems to be a current model (I did not know Ballantine was still in business).
http://www.ballantinelabs.com/323meter.htm
Good crest factor. A model 300 may be the early tube type.
.
glene77is:
If the LEDs are back to back we get twice the light output but a packaging problem compared to a diode with one LED. I do not know if anyone manufactures an LED package with a back to back pair of LEDs. The bridge rectifier method requires four diodes instead of one. All of this you know but maybe this will help others understand what has to be done in this type of circuit.
Somewhere I have some LEDs from the late 60s and sometime I will check their sensitivity.
From Wikepedia:
Any LEDs that I used prior to 1970 would not have cost more than about $1 each. By about 1972 or 1973 I started using 7 segment LED displays. Just prior to this I used displays with small incandescent lamps for each segment. It was not until the late 60s, maybe 67 or 68, that I could afford to experiment with RTL integrated circuits.
I believe in a previous post you described the development of a wide dynamic range log amplifier. To what use did you apply this? I believe in the 30s or 40s Ballantine or similar company manufactured a log AC voltmeter with vacuum tubes. Do you know what their design philosophy was?
This seems to be a current model (I did not know Ballantine was still in business).
http://www.ballantinelabs.com/323meter.htm
Good crest factor. A model 300 may be the early tube type.
.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
090315-1922 EST
glene77is:
Was your high quality full wave rectifier for a class project or something commerical?
In the HP 400H meter did they just put the meter movement in the center of a bridge rectifier and insert this in the feed back loop, or something else? I can not get to my manual easily to check.
.
glene77is:
Was your high quality full wave rectifier for a class project or something commerical?
In the HP 400H meter did they just put the meter movement in the center of a bridge rectifier and insert this in the feed back loop, or something else? I can not get to my manual easily to check.
.
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