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Dual jfets
Dual jfets
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Old 19th April 2017, 07:44 PM   #1
kinku is offline kinku  United States
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Default Dual jfets

Is one of the benefits of usng dual Jfets chips is their closely matched Idss?
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Old 19th April 2017, 07:53 PM   #2
WatrixReloader is offline WatrixReloader  Germany
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Yes and also thermal coupling. But if you match them by hand you might be better
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Old 19th April 2017, 08:49 PM   #3
kinku is offline kinku  United States
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Please explain a bit more. Dual Jfet are doped in atomic level to make the chip. When we do matching there are so many variables including the accuracy of instruments. So how that can be better than first.
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Old 20th April 2017, 08:50 AM   #4
WatrixReloader is offline WatrixReloader  Germany
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The production process is also varying. You have two ways to accomplish a dual jfet

1. two dies, one package
2. one die, one package (monolithic)

In case one you need to check every die and combine them by matching values. But two dies in one package might be more expensive and you need to measure every jfet ...sort etc. not sure if a company might do this for a cheap price. And thermal coupling is not really good compared to monolithic.

In the second case both jfets are on one die. It is possible to adjust production parameters so tightly that one can say that they are closely matched. But you will never get that close as mentioned in the case before. Or you have to throw away a lot of dies. But lower wafer cuts, easier to pack, just a few spot checks (eg 1 in 100 or 1 in 1000) to assume if the fets are in the production range (eg.: Idss matching Toshiba duals around 3% and Linear Systems around 10%)

If you do matching by hand you will have more or less case 1. For instance, you buy a batch of 100 parts and you will most probably find 1 pair idss matched below 1% (2sk170bl).

Keep in mind dual jfets are no "massproduct" if you compare them with other semiconductors so the price is higher anyway. Throwing away dies would drive the prices a lot more.

Last edited by WatrixReloader; 20th April 2017 at 08:53 AM.
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Old 20th April 2017, 03:03 PM   #5
kinku is offline kinku  United States
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Thank you!
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Old 20th April 2017, 04:21 PM   #6
WatrixReloader is offline WatrixReloader  Germany
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Denada
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