The LED ("Light Emitting DIODE") is common place now. In fact it seems
like they went from being simple "power on" indicator lamps to the
lighting of the future for darn near everything.
But what I dont understand is why they have never made a "Light Emitting
TRIODE"? (LET). It seems there would be many advantages!
Why dont they make a "Light Emitting TRIODE"
Started by ●January 24, 2015
Reply by ●January 24, 20152015-01-24
On 1/24/2015 4:13 PM, electron206@online.com wrote:> The LED ("Light Emitting DIODE") is common place now. In fact it seems > like they went from being simple "power on" indicator lamps to the > lighting of the future for darn near everything. > > But what I dont understand is why they have never made a "Light Emitting > TRIODE"? (LET). It seems there would be many advantages! >Can you list some of the advantages they might have?
Reply by ●January 24, 20152015-01-24
On Sat, 24 Jan 2015 16:23:06 -0500, Tom Biasi <tombiasi@optonline.net> wrote:>On 1/24/2015 4:13 PM, electron206@online.com wrote: >> The LED ("Light Emitting DIODE") is common place now. In fact it seems >> like they went from being simple "power on" indicator lamps to the >> lighting of the future for darn near everything. >> >> But what I dont understand is why they have never made a "Light Emitting >> TRIODE"? (LET). It seems there would be many advantages! >> >Can you list some of the advantages they might have?You could sell them to the crowd that believes in global warming ;-) ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
Reply by ●January 25, 20152015-01-25
On Saturday, January 24, 2015 at 1:23:08 PM UTC-8, Tom Biasi wrote:> On 1/24/2015 4:13 PM, electron206@online.com wrote: > > The LED ("Light Emitting DIODE") is common... > > But what I dont understand is why they have never made a "Light Emitting > > TRIODE"? (LET). It seems there would be many advantages!> Can you list some of the advantages they might have?One immediately comes to mind: power, ground, and modulation input are the three wires required for a laser transmitter. I generally see these in SFP form, with receiver wires as well... the seventeen other wires kinda obscure the triode nature of the beast.
Reply by ●January 26, 20152015-01-26
On Sat, 24 Jan 2015, electron206@online.com wrote:> The LED ("Light Emitting DIODE") is common place now. In fact it seems > like they went from being simple "power on" indicator lamps to the > lighting of the future for darn near everything. > > But what I dont understand is why they have never made a "Light Emitting > TRIODE"? (LET). It seems there would be many advantages! > >Because what's the use? If nothing else, it wouldn't be a triode in this day and age, while a "diode" did morph from describing a two element tube to a two element semiconductor device, other terms have been used to describe the terminal solid state devices. A diode is the way the device generates light. A "triode" implies some level of control, and that can be had with a separate device. It's not like in the old days where a magic eye tube was put in a glass envelope along with a triode, back then if you needed a triode to control the magic eye, leaving it separate would mean another tube, which were expensive and bulky, and would need another tube socket. There may be LEDs with seemingly built in controlling devices, but they would then be on the level of an integrated circuit, a transistor feeding an LED, not some device that combines a bipolar transistor and LED. Some optoisolators give the same function, I imagine. If the put a transistor in to drive the LED, then that's the same effect, you never notice if it's one device or not. It's a different case with an bipolar transistor that is light activated, I can't remember the name suddenly. There, the base is light sensitive, and since they figured out some functions for that (they needed to detect light, and needed some amplification) then they exist. Indeed, they are the receivers in those optoisolators.Sometimes the base is even brought out, so you can adjust the bias on the base, along with it being light controlled. Michael
Reply by ●January 26, 20152015-01-26
Michael Black wrote:> It's a different case with an bipolar transistor that is light activated, > I can't remember the name suddenly.** Phototransistor. Often photo Darlingtons are used in opto-couplers. ... Phil
Reply by ●January 26, 20152015-01-26
>"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 l= oad on whatever drives thee LED. They already pull little enough that micro= processors can usually drive the anyway but there is always the wattage rac= e. You could have power and ground busses where the LEDS are mounted and th= e processor coud drive the base which would presumably need less current. T= he base resistors could be built in like a digital transistor and it also x= ould be confihued as a current regualtor eliminating the limiting resistor = and making the device tolerant of more of a range of voltage.=20 I wouldn't be surprised if of all the companies in the world one of them tr= ied 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 transi= stor is used as a current regulator then you have dissipation. Unless you g= et 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.
Reply by ●January 26, 20152015-01-26
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 -- 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 26, 20152015-01-26
On Mon, 26 Jan 2015 15:14:06 -0500, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>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 HobbsSiGe transistors are super-duper ;-) ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
Reply by ●January 26, 20152015-01-26
On 1/26/2015 3:40 PM, Jim Thompson wrote:> On Mon, 26 Jan 2015 15:14:06 -0500, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> 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 > > SiGe transistors are super-duper ;-) > > ...Jim Thompson >Yup, the BFP640 is a fave. But the hole mobility of III-Vs is so horrible, and the minority carrier lifetime so short, that you can't get any beta no matter what you do. Those pesky direct bandgaps again. ;) 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
