[luvdunhill]

I'd like to match some 2SJ74 and 2SK170 JFETs by Vgs and was looking for a good way to do this. What about something as simple as the attached circuit, which was proposed by Nelson Pass to match the Lovoltech power JFETs.

See attached.

I also found this circuit, but it seems to be a bit more complex:

Another jig, but I'm not sure how to adapt it for the p-channel parts:

Any other thought on the matter? I understand how to match by measuring Idss at saturation, but this isn't what I'm looking to do.

 

[utilisateur]

Interesting i was about to post about matching the exact same devices and some PN4392s for Idss just yesterday.

[size=xx-small]I quit after deciding i had enough form matching 64 BC550 and 560 for hfe and already have matched 170s,74s and4392s which i guess are close enough.. [/size]

I guess this is no help but a free bump and my thoughts are with you

Maybe a matching tutorial should be stickied though!?

nearly forgot:

Have a look incase there is something helpful for you!

 

[luvdunhill]

heh, thanks for the bump. In my case, I'm not interested in matching for Idss. My plan is to match for Vgs then choose the highest Idss values.

 

[Pars]

Marc,

Not sure as I've only done FETs using Idss, but you are probably right as it seemed to me at the time that matching only by Idss wasn't resulting in the tightest matches.

I have a pdf, erno_borbely_on_jfets.pdf that seems pretty good, and has yet another matching circuit on it. As for your 2nd circuit, couldn't you just flip the batteries?

 

[luvdunhill]

Quote:

Originally Posted by Pars /img/forum/go_quote.gif Marc, As for your 2nd circuit, couldn't you just flip the batteries?

The more circuits the merrier, can you PM it to me?

I'm not sure about swapping the battery, as I think I would also need p-channel version of the BF246?

Anyways, I'm sure someone with the answer will chime in

 

[Pars]

Yeah, you probably would need the P-ch version of the other FET

I can't attach anything to a PM, and the file is too big to attach to the post. I think I have your email at home... I'll try to email it to you tonight.

 

[luvdunhill]

^

just ordered the BF246... I also tried with a LED-based CCS, for what it's worth.

any other comments before this thread dies?