Does JFET Idss change with temperature?

[andyr]

I heard somewhere that jfet Idss changes with temperature - the higher the temp, the greater the Idss will be.

Can anyone confirm this is true?

Thanks,
Andy

 

[MarcelvdG]

It changes, but I'm not sure in what direction.

 

[Nelson Pass]

Usually slightly positive.

 

[andyr]

It changes, but I'm not sure in what direction.

Thank you, Marcel. 👍

I'm pretty sure Idss increases with higher temperatures.

The reason for my question is as follows:
* I generally set the current passing through a jfet to be 70% of the Idss - as I understand this is well within the linear region of a jfet's operation. (I set the current by adjusting the Source resistor.)

* so if I have measured Idss (with my Peak Atlas DCA75) to be, say, 10ma ... I will set the Source resistor so that 7ma is passing through the jfet.

* but if I have measured Idss at, say, 18 deg C - then if the jfet is operating in a warmer climate ... Idss might increase to, say, 11ma?

* in which case, the 7ma passing through the jfet drops to only 64% of Idss - which is perhaps below the linear range?

* of course - if the increase in Idss at, say, 24 deg is only 10.1ma (up from 10ma at 18 deg) ... then that's not enough difference to cause a problem! 🙂

 

[andyr]

Usually slightly positive.

Thanks, Nelson! 👍

 

[rayma]

What’s All This JFET Constant-Current Stuff, Anyhow?​

https://www.electronicdesign.com/te...s-all-this-jfet-constant-current-stuff-anyhow

 

[radule]

Thank you, Marcel. 👍

I'm pretty sure Idss increases with higher temperatures.

The reason for my question is as follows:
* I generally set the current passing through a jfet to be 70% of the Idss - as I understand this is well within the linear region of a jfet's operation. (I set the current by adjusting the Source resistor.)

* so if I have measured Idss (with my Peak Atlas DCA75) to be, say, 10ma ... I will set the Source resistor so that 7ma is passing through the jfet.

* but if I have measured Idss at, say, 18 deg C - then if the jfet is operating in a warmer climate ... Idss might increase to, say, 11ma?

* in which case, the 7ma passing through the jfet drops to only 64% of Idss - which is perhaps below the linear range?

* of course - if the increase in Idss at, say, 24 deg is only 10.1ma (up from 10ma at 18 deg) ... then that's not enough difference to cause a problem! 🙂

There is zero tempco for jfets.
Erno Borbely say that zero tempco is at Vgs=Vp+0,63V

j113 Idss decreasing with temperature.
J170bl idss mostly incresing with temperature.

So, there is no general rule, it depends from actual jfet Vp.

 

[UniQ]

Erno Borbely say that zero tempco is at Vgs=Vp+0,63V

👍
Biasing JFETs to achieve zero drift AN-107 Interfet
https://www.interfet.com/jfet-datasheets/jfet-an-107-interfet.pdf