A Super-Simple LED Peak Flasher Audio Overload Clipping Indicator Using the TL431

[JR.]

here is TMI about 431 https://groupdiy.com/index.php?topic=74879.0



enjoy

JR

[terkio]

What are these area=2, what does it means in terms of BJT characteristics ?
What are these {1.8* R } I suspect R is a parameter, what is it's typical value ?

[JR.]

Simple resistance in ICs is factored by silicon area, so the ratios based on silicon area are easier to specify than precise resistance (thats my guess).

The article I linked to may explain.

JR

[terkio]

Yes, the article explains.

R is a scale factor, as I presumed. The author says about 100 Ohm.

area is emitter area
Transistors have different emitter areas
to achieve temperature compensation. To understand this, seems to need firstly to understand what they call "band gap".

[mediatechnology]

I really like die photos.

The die photo of the TL431 is in the original link: http://www.righto.com/2014/05/reverse-e ... ommon.html


Die photo of the TL431. Original photo by Zeptobars.

[JR.]

Back in the good old days they would publish schematics of ICs and I found them instructive.

Sometimes the schematics are not literal and simplified because they can fabricate semiconductor devices inside ICs like compound devices with dual emitters, collectors, or even multiple bases.

Back in the 70s the company I was a technician at developed a semi custom chip set with Monochip, a company that sold standard ICs with custom metallization layers, that provided customized functions using the standard library of integrated components connected together in different configurations. They included several of the oddball unconventional semiconductors (useful for making current mirrors and the like). To assist in bread boarding they provided discrete versions of these oddball semiconductors, so the breadboard would better reflect the final product.

JR

[mediatechnology]

Hans Camenzind's company.
Camenzind's book, Designing Analog Circuits, can be found here: http://www.designinganalogchips.com/

I've been wanting to scan the Interdesign brochure for a long time.
Not only did it have beautiful art it was also instructive.

[mediatechnology]

The Monochip MOC is like my Radio Shack 50 in 1 Science Fair Kit but at the microcircuit level.

[JR.]

Yes, I actually got to meet the man...... while one of his senior engineers (Jim Ball?) did most of the work on our project.

Yes the company was called Interdesign, the product was called monochip... lots of cobwebs in my memory banks about events from almost 50 years ago.

I am a little surprised the company did not enjoy wider success but it was still relatively expensive compared to dedicated ICs. Our design required something like 3 or 4 different monochips... a full custom IC might accomplish that inside one chip.

===

Decades later while at Peavey we seriously looked into developing a full custom IC for our most common circuit (audio power amp front end). We could accomplish this inside typical IC process constraints (<36V), but the apparent difficult part was integrating in an OTA, for a built in clip limiter. The junior engineer I worked with from the IC company did not even understand how an OTA worked. When I tried to explain to him that the OTA input long tail pair, needed to be well matched for Vbe to prevent control feedthrough. He told me no problem we'll just add degeneration resistors to the LTP... Obviously (but not to him) that would defeat the functionality of the OTA. I'm not sure if this was the straw that broke the camel's back or the high NRE, but we had to compete with a pretty low cost existing design (one OTA and one cheap opamp), so the project didn't happen. Real IC companies have difficulty making OTAs with low feedthrough. We had to buy a selected part for production so had to integrate a better than just a jelly bean OTA into our full custom IC.

JR