Electronics > Beginners
J112 JFET I_DSS - datasheet inconsistent?
aneevuser:
I bought some J112s from RS. The datasheet is here: https://docs.rs-online.com/1b2b/0900766b813d387a.pdf.
In the "On characteristics", it seems to suggest that I_DSS will be a min. of 5 mA (or 2mA ?) so I have tried to measure it for a couple of pieces assuming that it won't be too far off this value. However, I got no constant current behaviour with I_DS all the way up to about 50 mA, with a V_DS of 5 V, when the device began noticeably hot to the touch - it's dissipating 250 mW of a quoted max. of 350 mW.
Having taken another look at the datasheet, I note that Note 2 on page 4 states that "The electrical characteristics table indicates that an J112
has an IDSS range of 25 to 75 mA". Well, that may explain my observations, but it seems to contradict the "On characteristics" info, even assuming say a x5 variation in I_DSS between parts.
So the question is: WTF is going on here? Is the datasheet contradictory, or am I misreading it and confused? And what value should I typically expect for the I_DSS of a J112?
schmitt trigger:
Well..... I checked a datasheet from another vendor (Vishay), and it has the same contradictory values between the table of electrical characteristics and the Id vs Vds curves at different Vgs.
exe:
Well, 50mA is definetely more than 2mA or 5mA. So, I don't see a contradiction here since they only specify min value. They also don't provide typical value, so I wouldn't put any expectations based on "on characteristics".
J-fets are notorious for large parameter scattering :(. Even though modern production seems to be more consistent than datasheets often suggest.
What to trust? I'd say measurements. One can also put a hope that jfets from the same reel have close characteristic, but that's not guaranteed.
schmitt trigger:
You are correct. The datasheet only lists a minimum value. Maximum can be infinity and beyond.
MasterT:
The doc is edited version for J111, J112, J113. They missed to remove 2.0mA line, specification for J113.
And minimum 5.0 is o'k with "typical" 25-75.
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