TO-92 Current Mirror

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Samuel Groner

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Joined
Aug 19, 2004
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Location
Zürich, Switzerland
Hi

I believe that I have read in H & H that there is an integrated current mirror in TO-92 package from National; I don't have a copy at hand and Google didn't spite out a relevant link. Any ideas?

I found some SMD stuff from Phillips, but I don't like the low dissipation.

Samuel
 
I looked up the part in the art of electronics. The parts seems completely discontinued, but here is the datasheet:
http://www.avensonaudio.com/tech/tl011.pdf
TI TL011
 
A three-terminal device like this is missing an important extra degree of freedom, namely the ability to put some R's in the bottom emitters to trade off noise for bandwidth. If the 1:1 versions are used for the typical op amp input stage they add significant noise. Also if you look at the specs they aren't very impressive for current accuracy, considering that these are monolithic parts.

Why are parts going away? Of course it is at root economics, but behind the lower to zero volumes of parts sold is the general decline in any real knowledge of analog design.

I'm feeling unusually curmudgeonly today, but...

A former client now is using DSP EQ everywhere in new products as there is no one left there who knows how to design successful analog EQ. The speaker guy who uses the gui-based DSP card to flatten his new response now gets what he wants immediately without having to deal with the electronics people, which works for him. The fact that the resulting product costs more is important, but the time-to-market issues and management brownie points dispensed for adhering to schedule are overriding. And then the blurb writers can throw in a few more "digital" adjectives in their poop sheets. And we all know digital is better for everything, right?

"Orbiting this at a distance of roughly ninety-two million miles is an utterly insignificant little blue green planet whose ape-descended life forms are so amazingly primitive that they still think digital watches are a pretty neat idea." (HHG to the G).

Of course digital has its place, and refinements and extensions of it are to be respected and honored. And sales and marketing departments still have stringent requirements, like a two-drink minimum.
 
A three-terminal device like this is missing an important extra degree of freedom, namely the ability to put some R's in the bottom emitters to trade off noise for bandwidth.
True--I wondered why they didn't include them. Probably too expensive to match.

I found the BCV61/BCV62 parts which are essentially perfect for my application (current mirror for a balanced VAS)--but I need 50 V not 30 V! :cry:

Samuel
 
[quote author="bcarso"] is the general decline in any real knowledge of analog design.[/quote]
As an illustration, our dept. wanted to buy a successor for the old HP-spectrum analyzer workhorse, but HP/Agilent can't make them anymore like they used to. Fancy DSP etc etc, but real low noisefloor is another thing...
 
Could you use some sort of matched transistor pair for those?
http://www.diodes.com/datasheets/ds30449.pdf

Just an idea. Those run like $0.50 at mouser.
 
It's not clear from the datasheet if these are two isolated chips plucked from the adjacent spots on the wafer, as some earlier Diodes Inc. parts are, or if it is a monolithic pair. In any case absolutely no matching data is given!!

At least the earlier two-chip parts had some match data, although the parameters they elected to specify were not very useful for linear use.

Philips I believe also make some two-chip cheap pairs.
 
http://www.diodes.com/datasheets/ds30312.pdf
http://www.diodes.com/datasheets/ds30311.pdf

OK this was the one I was looking for.
It says matched in the datasheet. 2% Hfe Vbe Vce
Still $0.50 at mouser.
 
Thanks for the suggestions.

My basic intention for an integrated CM was parts count reduction and ease of assembly, not better current matching. So not sure what to do right now, but there is no hurry either!

Samuel
 

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