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Old 3rd April 2004, 11:51 AM   #1
Jena is offline Jena  England
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Unhappy Matching Mosfet's

Hello Fellows technicians.............

I'm wondering one things about the matching mosfet's.

I have read a lott in terms of this matter but there is a little bit opinions in terms of how many times you need for match mosfets.

Somebody said take less 1 minutes and write on the stick label a value.

Others said take for 10 minutes and write on the stick label the value.

But for my experience when myself matching the IRFp244 with 10 ohm resistance the VGS value it is not stable.

The same for IRF9610.

There is somebody that give me a right solutions and how I'll match correctly the Mosfet's it should appreciated a schematic for mosfets 244 and 9610.

Thanks in advance for an answer.

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Old 3rd April 2004, 02:56 PM   #2
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This topic has had alot of prior discussion. Have a look at this thread "Fuzzy on FET Matching". And, have you read Practical Mosfet Testing for Audio at the Pass DIY website?

Regards,
Dan
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Old 4th April 2004, 05:57 AM   #3
batee is offline batee  United States
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I found that the size of the heatsink affected this *a lot*.

Last month I was matching some IRF610s with Ids of ~2A.

I noticed that when I had a small heatsink attached (<4in^2), they continued to climb in temperature over the next 30 minutes, and Vds changed accordingly.

When I had a large heatsink (240in^2) attached, they stayed relatively cool over the next 30 mins and Vds was much more stable.

In all cases, I waited until the fourth digit to the right of the decimal (the 100uV digit) stopped changing, then decided that was good enough.
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Old 5th April 2004, 06:23 AM   #4
Mad_K is offline Mad_K  Norway
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I use 10 seconds (recommended by Nelson) and are getting very good matches
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Old 5th April 2004, 07:23 AM   #5
jwb is offline jwb  United States
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I attach them to a heater. You want them operating at steady state. You could also plot Vgs versus temperature, or Vgs versus current, or both. The more sophisticated your matching technique, the better match you will get.

Also I recommend loading them with a current source instead of a resistor.
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