In article <54C6A00E.6010708@electrooptical.net>, pcdhSpamMeSenseless@electrooptical.net says...> > On 1/26/2015 10:41 AM, jurb6006@gmail.com wrote: > >> "Can you list some of the advantages they might have?" > > > > That's what I was thinking. The only thing I can think of is to lower > > the load on whatever drives thee LED. They already pull little enough > > that microprocessors can usually drive the anyway but there is always > > the wattage race. You could have power and ground busses where the > > LEDS are mounted and the processor coud drive the base which would > > presumably need less current. The base resistors could be built in > > like a digital transistor and it also xould be confihued as a current > > regualtor eliminating the limiting resistor and making the device > > tolerant of more of a range of voltage. > > > > I wouldn't be surprised if of all the companies in the world one of > > them tried the idea but nobody bought them. I can only think of that > > one advantage to it, and that would not be worth the extra cost IMO. > > Also, if the transistor is used as a current regulator then you have > > dissipation. Unless you get wild and put a switcher in there. Then > > you are talking a coil csuae you can't pulse the LED with overcurrent > > and expect it to last. The cost might end up being a dollar insrtead > > of the few cents a regular LED and resistor cost. > > > > Making bipolar transistors out of III-V semiconductors (e.g. GaAs, InAs, > AlGaAs, InGaAs, InP, GaN, etc) is difficult, and they don't work very > well. Plus the extra constraints would make the LET much harder to build. > > The main issue in LED design is that the primary photogeneration is very > efficient, but the photons are generated deep inside the die, and it's > really hard to get them out efficiently. If you just use a regular GaAs > PN diode, all the light gets absorbed by the top semiconductor layer. > > Then there's the 95% or so that you lose to total internal reflection > (taking into account the Fresnel reflection of the light that does make > it out), and the 50% you lose due to half the light starting out going > the wrong way.... > > Modern LEDs are heterojunctions, with transparent semiconductor layers > top and bottom to reduce absorption, and controlled roughening of the > surfaces to let the light rattle around till it escapes. > > Cheers > > Phil HobbsRattle around, that's so sophisticated of you, Phil! Jamie
Why dont they make a "Light Emitting TRIODE"
Started by ●January 24, 2015
Reply by ●January 26, 20152015-01-26
Reply by ●January 27, 20152015-01-27
On 1/26/2015 9:53 PM, Maynard A. Philbrook Jr. wrote:> In article <54C6A00E.6010708@electrooptical.net>, > pcdhSpamMeSenseless@electrooptical.net says... >> >> On 1/26/2015 10:41 AM, jurb6006@gmail.com wrote: >>>> "Can you list some of the advantages they might have?" >>> >>> That's what I was thinking. The only thing I can think of is to lower >>> the load on whatever drives thee LED. They already pull little enough >>> that microprocessors can usually drive the anyway but there is always >>> the wattage race. You could have power and ground busses where the >>> LEDS are mounted and the processor coud drive the base which would >>> presumably need less current. The base resistors could be built in >>> like a digital transistor and it also xould be confihued as a current >>> regualtor eliminating the limiting resistor and making the device >>> tolerant of more of a range of voltage. >>> >>> I wouldn't be surprised if of all the companies in the world one of >>> them tried the idea but nobody bought them. I can only think of that >>> one advantage to it, and that would not be worth the extra cost IMO. >>> Also, if the transistor is used as a current regulator then you have >>> dissipation. Unless you get wild and put a switcher in there. Then >>> you are talking a coil csuae you can't pulse the LED with overcurrent >>> and expect it to last. The cost might end up being a dollar insrtead >>> of the few cents a regular LED and resistor cost. >>> >> >> Making bipolar transistors out of III-V semiconductors (e.g. GaAs, InAs, >> AlGaAs, InGaAs, InP, GaN, etc) is difficult, and they don't work very >> well. Plus the extra constraints would make the LET much harder to build. >> >> The main issue in LED design is that the primary photogeneration is very >> efficient, but the photons are generated deep inside the die, and it's >> really hard to get them out efficiently. If you just use a regular GaAs >> PN diode, all the light gets absorbed by the top semiconductor layer. >> >> Then there's the 95% or so that you lose to total internal reflection >> (taking into account the Fresnel reflection of the light that does make >> it out), and the 50% you lose due to half the light starting out going >> the wrong way.... >> >> Modern LEDs are heterojunctions, with transparent semiconductor layers >> top and bottom to reduce absorption, and controlled roughening of the >> surfaces to let the light rattle around till it escapes. >> >> Cheers >> >> Phil Hobbs > > Rattle around, that's so sophisticated of you, Phil! > > Jamie >Well, that's pretty much what happens. Listen carefully and you'll hear it. ;) Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●January 27, 20152015-01-27
>"The main issue in LED design is that the primary photogeneration is very >efficient, but the photons are generated deep inside the die, and it's >really hard to get them out efficiently."IIRC that was the holdup with the blue LEDs in the beginning. the rest were two cents and the blue ones were a buck. One thing I found out is that the white ones mostly have a phosphor. That is probably what made them suitable for use in LCD TVs. If you had red, green and blue LEDs the output was too spikey for good colorimetry. That was probably a bad move for TV engineers because dropping the TV would bereak the CCFLs in there sometimes. I guess they'll just have to make the PC boards thinner and brittle.
Reply by ●January 28, 20152015-01-28
On Tue, 27 Jan 2015 18:49:52 -0800 (PST), jurb6006@gmail.com wrote:>>"The main issue in LED design is that the primary photogeneration is very >>efficient, but the photons are generated deep inside the die, and it's >>really hard to get them out efficiently." > >IIRC that was the holdup with the blue LEDs in the beginning. the rest were > two cents and the blue ones were a buck. >Why were the blue ones so costly?>One thing I found out is that the white ones mostly have a phosphor. That is > probably what made them suitable for use in LCD TVs. If you had red, green >and blue LEDs the output was too spikey for good colorimetry.Are you saying that LED tv screens use white LEDs? (as if they were using florescent bulbs?). I thought the colors themselves were created by RGB the same way as the old CRT sets? (I have not kept up with these newer equipment).> >That was probably a bad move for TV engineers because dropping the TV would >bereak the CCFLs in there sometimes. I guess they'll just have to make the PC >boards thinner and brittle.You're not suppposed to drop tv sets :)
Reply by ●January 29, 20152015-01-29
On Wednesday, January 28, 2015 at 5:32:50 AM UTC-8, elect...@online.com wrote:> On Tue, 27 Jan 2015 18:49:52 -0800 (PST), jurb6006@gmail.com wrote:> >... the holdup with the blue LEDs in the beginning. the rest were > > two cents and the blue ones were a buck. > > > Why were the blue ones so costly?They have a large bandgap (an energy range where the quantum mechanics of the solid material does not allow any solution to the electron wave equation). Only a single-event hop, across a large bandgap, by an electron, can create light emission of the required type. Large bandgap => high frequency light emission (blue end of spectrum) Small bandgap => low frequency light emission (infrared) That means most materials are unsuitable, right off the bat. Then, it implies that the possible impurities that would create solutions in the bandgap range are many (and the semiconductor junction won't emit light if those are allowed, or even if microscopic strains and voids are allowed). The earliest usable semiconductor devices were Ge based, because the low bandgap made impurity sensitivity less troublesome than with Si. It was only after decades of Si device production that the first 'coppermine' chips used copper for wiring, because copper is an important impurity and would ruin silicon devices if it weren't carefully contained/controlled. Another problem, that's hard to explain, is the three-dimensional nature of the 'bandgap'; some materials (silicon being one) have an "indirect bandgap", meaning that an electron transition from lowest-energy-of-high-band to highest-energy-of-low-band requires a momentum change. There's no (not much) momentum in the photon, so another particle must be involved: the complication here, is that the 'single-event hop of an electron' is a fast event, while a dance with other particles involved is slow (and for practical purposes, that means it's disallowed). Those guys with the Nobel prize for getting it all right, explored many paths of the maze before they found a useful blue glow.
