Wha do you think about using 2sk369(very high ransconducance j-fet) as a curren source or sink? I mean pros and cons...
I need a 5ma low noise current source o bias some zenners and i have some of these but i remember some people not recommending high transconductance transistors against bf256c .I was thinking more about using a tl431+bjt composite ccs to be honest , but a 2sk369 fet looks like the simplest way to achieve it.
I also have some 2n5464 (p channel) that could do the job, but the current spread goes as low as 2ma for 0v Vgs and i need a solid 5ma current source.J112 , 174, 2n5460, 2n5457..I know that higher GS resistors usually give better current regulation, but 2sk369 graphs look pretty linear even with a 20 ohms source resistor.
Might probably be better to use two sk369 in parallel with like 51 ohm source resistor as a bzx 55 zener would still work fairly well at a total of at 4ma.
The current source noise is an important factor for me as well.
I need a 5ma low noise current source o bias some zenners and i have some of these but i remember some people not recommending high transconductance transistors against bf256c .I was thinking more about using a tl431+bjt composite ccs to be honest , but a 2sk369 fet looks like the simplest way to achieve it.
I also have some 2n5464 (p channel) that could do the job, but the current spread goes as low as 2ma for 0v Vgs and i need a solid 5ma current source.J112 , 174, 2n5460, 2n5457..I know that higher GS resistors usually give better current regulation, but 2sk369 graphs look pretty linear even with a 20 ohms source resistor.
Might probably be better to use two sk369 in parallel with like 51 ohm source resistor as a bzx 55 zener would still work fairly well at a total of at 4ma.
The current source noise is an important factor for me as well.
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I think you are better of with an high Idss like the J108
For 5mA a source resistor about 1k and that gives a practically horizontal Id-Vds curve.
Mona
For 5mA a source resistor about 1k and that gives a practically horizontal Id-Vds curve.
Mona
unfortunately i can use only what i have at hand for the moment...i'm on very low budget for some time and i can only take advantage of the components i already have.
I think i'm gonna go with 2 x j112 in series at Vgs=1v for 2 ma drain current which leave me the choice of a 470...510 ohm resistor.The bzx55 zenner dynamic resistance is about 2...300 ohms plus 200 ohms rds on which should be fine for a maximum 140uA base current that should be possible in my circuit. There's a 10k ohm resistor in series with the zenners anyway.
I was considering a cascode made out of 2sk369 and a j112, but i'm not sure how 2sk369 would behave at 0.8 v VDS and 2 ma current through it...From what i have read cascode thermal behavior is worse than two j-fet in series and two j-fet in series should also be better if the voltage gets too high on them .
I was considering a cascode made out of 2sk369 and a j112, but i'm not sure how 2sk369 would behave at 0.8 v VDS and 2 ma current through it...From what i have read cascode thermal behavior is worse than two j-fet in series and two j-fet in series should also be better if the voltage gets too high on them .
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