[sdiy] Matching transistors

[James Patchell]

Certain circuit function require that transistor parameters track over 
temperature, in order for that to happen, they need to be the same 
(matched).  You can match your own transistors by purchasing a batch of 100 
parts and then measuring Vbe at a fixed current.  You will find a circuit I 
use to match mine on my website below.

The easiest way is to purchase pre matched transistors, although, they are 
getting harder to find, and they are not cheap.  MAT02, MAT03, MAT04, 
THAT300, THAT320, THAT340, SSM2220, LM394....etc....is a short list of 
matched transistor types, and their prices range from $3 to $12 each, 
depending on the degree of matching.  For premium performance, the pre 
matched transistors are by far the best.

The best example of a required use of matched transistors is in the 
exponential converter in synthesizer modules.

At 02:30 PM 12/3/2005 +0100, you wrote:
>What's the deal about those matching transistors?
>Why and where do they have to match and how do I know I got matched ones?
>
>cheers,
>ToAd
>
>--
>Tom Adam
>The Big Ear
>http://users.pandora.be/the-big-ear/
>Check out the download section!
>

         -Jim
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http://www.oldcrows.net/~patchell

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