[tangent]

Quote:

Why this extremely long URL's?

Ask Analog's webmaster.

 

[jeffreyj]

Yeah, tangent, despite the man behind the curtain (pay no attention to him!) I am human...

When Bob Pease of Nat.Semi. fame describes in one of his books that he can never remember which terminal on LEDs is positive, that he has to derive it every time, I totally identify with that. I always ignore the flat and instead look at which lead connects to the reflector to figure it out...

I just looked at the Jung thread on diyaudio.com - poor Per Anders! Fred Dieckmann (sp?) immediately concluding that Per was going to use all of the "valuable" information from diyaudio to pursue a commercial venture was, to me, nothing short of hypocritical - but Fred is one of the most offensive members over there. I was really surprised at how vitriolic Jan Didden was in some of his posts; definitely lowers my estimation of the man. Too bad that it's just a few of the members there that make the place so unfriendly... unfortunately, the most prolific posters.

ppl - the Vbe article by Pease is a great read but I find that the -2.1mV/C approximation is most useful most of the time, even if the true variation depends quite a bit on Ic.

edit: grammar

 

[ppl]

Quote:

Originally posted by jeffreyj Yeah, tangent, despite the man behind the curtain (pay no attention to him!) I am human... When Bob Pease of Nat.Semi. fame describes in one of his books that he can never remember which terminal on LEDs is positive, that he has to derive it every time, I totally identify with that. I always ignore the flat and instead look at which lead connects to the reflector to figure it out ppl - the Vbe article by Pease is a great read but I find that the -2.1mV/C approximation is most useful most of the time, even if the true variation depends quite a bit on Ic. edit: grammar

The Man behind the curtain! Where have i seen that before.

Have to look at which lead connects to the reflector to figure it out
Me Also i do exactly the same thing in addition to getting Jfets backwards. Humm there must be a virus going around cause it seams widespred.

I would have thought the change in Vbe vs tempature would have been taken as a given since alot of temp probes are based upon the Vbe change with tempature.

 

[jeffreyj]

Quote:

Originally posted by ppl The Man behind the curtain! Where have i seen that before.

Not in Kansas, that's for sure!

Quote:

I would have thought the change in Vbe vs tempature would have been taken as a given since alot of temp probes are based upon the Vbe change with tempature.

It is a given, as long as the operating current is constant and known. In other words, randomly selecting a current to bias the junction will give a random slope of Vbe vs. temperature as the result.

From another perspective, it's just the flipside to the logarithmic change in Vbe vs. current for a given temperature.

 

[tangent]

It's a good habit to get into, using the reflector inside the LED to identify the cathode. There are a few LED types where the long lead is the cathode, backwards from 99% of all other LEDs.

 

[ppl]

LOL JefferyJ I knew that was from the Wizard of Oz however I failed to see it’s relevance hear or to this subject. I must admit I am not a literary Genius and this one flew above my head.

The inverse relation ship of Vbe vs temperature is a given. I would also assume that most designers understand that the emitter resistance of the transistor (Re) declines as operating current is increased. And as such also understand the interdependence of Vbe on operating current and temperature. This interrelationship is why Bias diodes are attached to the Heat sinks of Audio Amplifiers. Thermal runaway will result if one dose not account for these interrelated aspects of bipolar transistors.

 

[jeffreyj]

Quote:

Originally posted by tangent It's a good habit to get into, using the reflector inside the LED to identify the cathode. There are a few LED types where the long lead is the cathode, backwards from 99% of all other LEDs.

Believe me, it's nothing so noble as a habit on my part - more of a crutch

Quote:

Originally posted by ppl LOL JefferyJ I knew that was from the Wizard of Oz however I failed to see it’s relevance hear or to this subject. I must admit I am not a literary Genius and this one flew above my head.

Oh, I stuck that in there because Warren was giving me a hard time about being human after all - typical sore winner behavior on his part

Quote:

I would also assume that most designers understand that the emitter resistance of the transistor (Re) declines as operating current is increased. And as such also understand the interdependence of Vbe on operating current and temperature. This interrelationship is why Bias diodes are attached to the Heat sinks of Audio Amplifiers.

This is pretty much what I was getting at earlier without zipping my fingers around to type it: you can't reliably compensate a power transistor by running a few uA through the biasing diode!