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Old 29th May 2013, 09:52 PM   #21
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Quote:
Originally Posted by LucasAdamson View Post
Will jfet IDSS measure differently after burn-in, I wonder?
I would expect them to be very very close, especially if they are at the same temperature as previous measurements.
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Old 30th May 2013, 09:53 AM   #22
AndrewT is offline AndrewT  Scotland
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I will be more blunt and state:
In my opinion "burn in" does not exist.
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Old 30th May 2013, 01:27 PM   #23
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Does metal migration exist on IC chips?

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Old 30th May 2013, 01:44 PM   #24
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Quote:
Originally Posted by Zen Mod View Post
if you really burn them
I'd burn them in a little at a time.
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Old 23rd October 2016, 09:23 AM   #25
teleman is offline teleman  Norway
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I'd like to construct this circuit to test and grade a few JFETs I have.
Can I run a J201 on a 12v circuit?
Can I substitute a pot instead of the Rset-10k- resistor?

Thanks
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Old 23rd October 2016, 09:55 AM   #26
AndrewT is offline AndrewT  Scotland
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A stepped/switchable resistor could be substituted.
A pot would end up with an unknown value (and unknown current) after you have played with it.

12V should be OK with all 10Vds Idss test devices.
Some devices test Idss at a lower voltage. You may have to use a lower supply for these.
You can check you circuit with higher Vds devices and see what range of voltage is applied across the Drain Source as gm and Idss is varied.
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Old 23rd October 2016, 10:31 AM   #27
teleman is offline teleman  Norway
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Quote:
Originally Posted by AndrewT View Post
A stepped/switchable resistor could be substituted.
A pot would end up with an unknown value (and unknown current) after you have played with it.
Thank you AndrewT, you're right about ending with an unknown value! I suppose I can build a stepped resistor using a multi turn rotary switch? I have only a 4 turn switch, which I suppose won't quite cover the test range? I should have a 12 turn switch somewhere! I thought I could measure the resistance after every test, but too tedious I agree.

I could also make a 9v battery connection for devices which need lower Vds.
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Old 23rd October 2016, 10:39 AM   #28
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I would be very careful with this circuit because if you don't know the Idss of the DUT up front, the opamp will easily force it into positive bias.
So you need to watch Vgs very closely and slowly increase the test current.

It is useful if you want to pick JFETs at a bias known to be below its Idss.
Not useful for curve tracing unless you know exactly what you are doing.


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Old 2nd November 2016, 02:20 PM   #29
teleman is offline teleman  Norway
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Having ordered a few T071s and resolved to a long wait, I then realized that I do have plenty of T072s on hand. So thought i'd use one of these instead! But I need to terminate one of these inputs. It's been a very long time since I did this hence hope the diagram below which I found elsewhere to which I've added the resistor values are correct.
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Last edited by teleman; 2nd November 2016 at 02:28 PM.
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Old 2nd November 2016, 02:26 PM   #30
teleman is offline teleman  Norway
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Oops...pin terminals added!
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