Transistor Test Jig

Hi

For some (rare!) applications I want to be able to match transistor pairs for beta and Vbe. As using a DVM to measure both parameters for each transistor and selecting pairs afterwards tends to be potentially imprecise (mostly due to the large tempco of Vbe and the lack of collector current control) I want to build a dedicated test jig.

It should allow me to match transistors with a beta of 50-1500 at collector currents from 150 uA to 3.5 mA to a precision of <5% (beta) and <1 mV (Vbe). My idea is to first measure beta for every transistor and afterwards testing matching pairs for the Vbe difference (rather than trying to measure Vbe directly). For the later I've come up with the following circuit: [removed]

For measuring beta I've found a schematic by John Chester: [removed]
However at the lower range of collector currents and higher beta range my DVM would need to measure down to the nA range which is asking too much. Any other circuit ideas for this? Comments for my circuit? Thanks!

[Edit new revision: transistor_test_jig_r1.pdf]

Samuel

This looked interesting, but I don't know how well it will work for your matching.

http://www.elecdesign.com/Articles/Index.cfm?AD=1&ArticleID=6251

Cool article Brad!
I need a matching scheme for these D B X 2001 DIY's and that looks like the ticket.

Note the need to have the transistors already matched for certain parameters before using that jig.

I would add a Voltmeter to the Chester circuit to measure Vce.

Thanks for your answers. In the meantime it occured to me that it's pretty simply to modify my test jig to measure beta as well by simply removing the 10 ohm resistors in the feedback network (R106/R108 and R206/R208). Measuring the voltage drop across the remaining 10k resistors reveals the according beta.

For your first circuit I've got some THAT 300 and THAT 320 matched quads for the BC550/560s.

Click to expand...

A Monte Carlo analysis indicated that the matching of these transistors isn't that critical. However I haven't gotten a clue what transistor parameters get randomised so this might be wrong.

www.elecdesign.com/Articles/Index.cfm?AD=1&ArticleID=6251

Click to expand...

I remember having seen this circuit before. I guess matching for more parameters would be one step further, but for my needs it is simply too much, I think.

Samuel

Finally got around building and using this thing. In case there is any interest I linked the latest revision in the first post.

I did build mine with BC550C/BC560C instead of the denoted Toshiba parts which was a mistake as the later are way more consistent. For finding 14 pairs (28 transistors) with hFE matched to 1% I needed to measure a mere number of 37 transistors. The maximum hFE difference within this lot was 23%. :shock:

Vbe seems to be much more consistent as well compared with the BC550C/BC560C from ON Semiconductors, though I did not explore this too much yet. The jig has pretty high Vbe matching resolution--inserting a MAT02E showed an offset of 100 uV, quite good enough I'd say!

Samuel