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woody 28th February 2011 12:33 AM

Parallel jfet question
 
1 Attachment(s)
In paralleling a couple of jfets how close do they need to match. Taking
the jfet BOZ for example if I wanted to run a pair of 170's in parallel instead of one jfet would I just match for idsa withen a ma or so. I have
something compleatly different I am just refering to this circuite as an example.

jackinnj 28th February 2011 01:00 AM

I match to 0.1mA Idss -- and then compare the gm of the matched sets.

fwiw, Pbf 2SK170's are pretty available now...

Samuel Groner 28th February 2011 08:06 AM

In such a configuration matching is not critical as it only determines current sharing amongst the transistors; the paralleled transistor will effectively form a single transistor with higher Idss, matched or not. Just use an individual 10r source resistor for each transistor and you're fine.

Matching is important for differential pairs as this will affect DC offset, drift and CMRR/PSRR. But that's not what we have here.

Samuel


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