Beta degradation quantified?

I don't know of any specifics. I just know that repetitive breakdown DOES degrade the beta.

Can't you put a diode there to prevent it?

...Jim Thompson

Yes, I could use a diode (not directly across) but would prefer to avoid it if it won't affect the reliability. I only need a beta of

Best regards, Spehro Pefhany

For what period of time, and what temperature? Eventually the beta does go away. When running breadboard tests under the hood of a car the transistors died in about two weeks.

...Jim Thompson

Benign environment, but it is intended to last 'forever'. Maybe I'll check it out if no-one else has done any tests. Whatever the problem extent is, it doesn't seem to be severe enough that people worry too much about ESD on regular BJTs and bipolar transistors. Do you happen to know if there is a diode structure in an SN7400 input?

Best regards, Spehro Pefhany

There ARE diodes protecting the inputs of an SN7400.

Good to see that you are using such modern parts ;-)

...Jim Thompson

Hmm.. it's a lateral PNP, right? So it should have a relatively high E-B breakdown according to Camenzind. No, I'm not using 7400s (though you can still buy them) just a faint echo of the internal circuit.

Best regards, Spehro Pefhany

Le Tue, 18 Sep 2007 13:39:59 -0400, Spehro Pefhany a écrit:

I did take some quick measurements once:

Thanks, Fred. Two hours at a punishing 30mA! That's a lifetime here, and only a 16% drop. I can stand a 90% drop.

Best regards, Spehro Pefhany

to

My thanks also, Fred. Let's call the 50% drop at 180mAHr the Fred Rate. It the Fred Rate linear over time and current? Is it consistent with different devices?

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Have you tried a beta test? ;-P

Cheers! Rich

So now there is a Fed Rate and also a Fred Rate :-)

No, I'm more of an alpha geek.

Best regards, Spehro Pefhany

Base Fredgradation.

John

Pretty soon folks on this here newsgroup will ask what the Bartoli-coefficient for the 2N2369 is :-)

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Yes, we should. This data should really be in the transistor spec, as soon as we agree on what to call it.

OK, one Bartoli is how many mAh it takes to drop beta to 1/e of its original value.

John

Fred performed a lot of valuable transistor measurements, also about noise. Would be nice if that was all published somewhere on the web in one place. Kind of a hangout for analog guys. The real ones, who still do tough transistor-level designs.

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I have no problem with that, but 1/2 might be easier for the marketing type.

"Spehro Pefhany"

Kindly quantify the length of a piece of string for us first.

OK ??

...... Phil