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Old 7th November 2013, 06:06 PM   #1591
RCruz is offline RCruz  Switzerland
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please post a jpg or png... you can capture screen image and paste it on windows paint... edit it, save it as png and there you go.
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Old 7th November 2013, 06:54 PM   #1592
EUVL is offline EUVL  Europe
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Sir,

I have a jpg of the data.
I have also plenty of previous experience uploading such files onto the forum.
But in the last hour or so, none of the numerous upload attempts I made went through.
Not by iexplorer, not by firefox, .......

Since I have no problem uploading files to other forums this evening, maybe the problem is not with me.


Cheers,
Patrick
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Old 7th November 2013, 10:54 PM   #1593
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Other people have reported the same issue as well.
For the time being, I thing the best bet is to upload on a Dropbox folder, copy the public link and paste it here (preferably into [IMG][/IMG] tags).
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Old 8th November 2013, 01:07 AM   #1594
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It is being addressed.
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Old 8th November 2013, 08:10 AM   #1595
EUVL is offline EUVL  Europe
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Finally.

We also measured 3 examples of J111 in the meantime.
Same results -- zero tempco about 2mA.


Patrick
Attached Images
File Type: png 2N4391-0004.png (43.6 KB, 497 views)
File Type: png J111-vartemp.png (101.3 KB, 492 views)
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Old 8th November 2013, 10:02 AM   #1596
Calvin is offline Calvin  Germany
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Hi,

due to the negative Temp-coefficient one doesnt need to worry too much as the bias point will stabilize whilst warm-up. There may be a slight offset from optimum for the warm-up time, but that dosent matter too for the output of the complete circuit.
In my SE-designs for the current sourcing DACs like PCM1792/94/95/96 I never had an issue with the current source not stabilizing at the desired bias.
So as long as the JFET is kept below its heat power limits, I see no real reason to use paralleled multiples of them, instead of a single one.

jauu
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Old 8th November 2013, 11:06 AM   #1597
EUVL is offline EUVL  Europe
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Calvin,

In post #1586 above, we mentioned that the tempco at 6mA was -3A/C.
Assuming a Riv of 680R, this means a tempco for the output DC offset of 2mV/C.
Or 10mV for an ambiet temperature change of 5C.

So the issue was not stabilisation.
The issue was DC offset dependent on ambiet temperature.
In Asia and probably also in Southern Europe, room temprature change of 5~10C is normal.
One can then argue whether 10~20mV offset is too much or not.

We just want to publish our findings.
One can decide for himself what solution he wish to choose.

The next thing we might wish to investigate is whether SMD devices behaves the same.


Best,
Patrick
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Old 8th November 2013, 11:16 AM   #1598
bkdog is offline bkdog  Australia
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Thanks Patrick - as one who has followed this from the beginning, the result is very interesting and it is a perplexing problem. Maybe SMD devices will behave differently, only experimentation will tell. Even a device (resistor for example) with a tempo of +3A/C would possibly not remain that way after 12 months or more

Good luck and more solder to your iron! (or whatever aphorism is suitable)
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Old 8th November 2013, 11:38 AM   #1599
EUVL is offline EUVL  Europe
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If you want a long-term secured solution, then I suggest you use MAX6126.
There is a circuit to configure it as a current source in the datasheet.
And it is quite low noise.

For those who like living dangerously, 2N4391 is a good solution.
And there are enough variants being discussed to suit all tastes.


Patrick
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Old 8th November 2013, 08:54 PM   #1600
RCruz is offline RCruz  Switzerland
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I like the MAX6126 chip... but why do you say one must like danger to use 2N4391 ? due to the high Idss ?
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