LED forward voltage drop with temperature

It was just a little breadboard. The temps on all the parts were similar.

I don't have a Spice model of any of the LEDs that we have in stock. I'd have to measure one over current and temperature and verify a Spice model. It was easier to build the circuit. I'd want to do that anyhow to verify the model.

The trick of this circuit is that the LED has more voltage drop than the transistor be junction, but a similar absolute TC.

Light doesn't seem to matter. Makes sense. The LED is making a lot of light, and it's very close to the LED.

Exactly. The LED tempco mostly cancels the Vbe tempco.

Are you sure ? LED is not a silicon based component so I'm not sure they have the same tempco.

It works.

Different LEDs have slightly different tempcos. The bandgap goes up as the lattice contracts, and the thermal effect goes the other way.

LEDs are direct-bandgap devices, so there are radiative as well as nonradiative branches, which depend differently on the details of the band shapes.

LEDs and lasers nearly always tune towards the blue at low temperatures, but George's one tunes the other way.

Cheers

Phil Hobbs

============

**FYI:

Silver, copper, gold, aluminium, magnesium, tungsten, zinc, nickel, tin, iron, platinum, mild steel, lead plus some alloys ALL have the same positive tempco of resistance.

Close to .004% per C.

.... Phil

Sure although it is not "%" in that case.

Anyway we did not speak about metals, it was about tempco of IV-V (silicon) and III-V materials.

It's a fairly well known fact.

============

Anyhow the fact is YOU are 100% WRONG !!

FOAD

..... Phil

Pointing out a factor of hundred error is being pedantic?

Interesting.

Jeroen Belleman

=======================

.... Phil

LTDM

(learn to do math)

Only "Allison-100%-wrong", allows himself speaking before thinking! I suspect the Allison did not really understand what % really mean.

But he wasn't 100% wrong. He was 10,000% wrong.

snipped-for-privacy@highlandsniptechnology.com wrote in news: snipped-for-privacy@4ax.com:

I was sure you were referring to Trump and his family of fuckups.

"Allison Coeff" --> 0.004% gives a coeff = 0.00004; 4.10-5

TC metals (Physics) = (approx.) 0.004; 4.10-3

An error magnitude of 100 between "Allison" and real Physics.

We need a new SI unit of wrongness, Allisons. We can't apply that to the linux guy, since he is Always Wrong.

Obscure note: electrons conduct heat and electricity, which track. So most metals and alloys are about 150,000 K/W per ohm.

I suppose then that thermal conductivity should have the same temperature coefficient as electrical conductivity.

What's the thermal conductivity of a superconductor?

from now we will name it so, Allison's SI

with Allison's SI

I guess W/K.m is about 10e5 or 10e15 or something like that for a supra conductor material, Sure that Allison has another figure based on own SI ?

nickel, tin, iron, platinum, mild steel, lead plus some alloys ALL have th e same positive tempco of resistance.

Whoever came up with a name for water wasn't a fish. Superconductors don't ask questions about conductivity. Superfluids have no thermal resistance and so ask no questions about the flow of heat.

If people were superfluid to determine if I had a fever you would take your own temperature.

Low-temperature metallic superconductors are lousy thermal conductors; Pauli exclusion principle, almost all of the lower-energy states are filled and there aren't many empty states between kT and the energy gap for the higher energy ones to move into, either.