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Old 15th June 2007, 08:08 PM   #1
Tom7227 is offline Tom7227  United States
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Question IRF640 vs IRF640N

I hope someone has input, or perhaps experiance with this.

I have a Fusion Amp with 1 bad IRF640 output MOSFET.

Power supply was destroyed and after hours of endless troubleshooting, got it running.

Problem is I have all kinds of 640N's and NO 640's..

Whats the opinion of mixing these?

I know the 640N is the lead free version...

Tom
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Old 15th June 2007, 11:36 PM   #2
KyferEz is offline KyferEz  United States
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I'd say replace all of the supply fets w/ the 640N, otherwise you are likely to have trouble. Why? because of a slightly different manufacturing process, and differing date code of the parts.

Even identical parts should be from the same "batch" when replacing FETs used in parallel.

My 2 cents.

KyferEz
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Old 15th June 2007, 11:41 PM   #3
Tom7227 is offline Tom7227  United States
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Thank You,

I was able to find one IRF640.... Install it and worked good..so far.

I was trying to avoid replacing (20) 640's... to 640N's

perhaps if this comes back.. I will have to change them all.
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Old 16th June 2007, 08:03 AM   #4
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Theres a simple fet tester over in the Pass forum section that will let you at least try to match ON characteristics enough that you will at least be in the ball park when replacing Mosfets in array's.

I have never found date codes that reliable as a matching guide, but others here disagree with me on this saying it has worked well for them. So its sorta a question of time and money.

Guess I am old fashioned about matching semi's. I would at least try to get the nomenclature the same and the same maker of course, Or just replace the whole bunch with the same exact part from the same maker for symmetry if nothing else. IRF-640's are fairly cheap in quantity's that I buy. They cost like 18 cents each purchased in bulk quantity's.

Good luck on your repairs
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Old 16th June 2007, 06:49 PM   #5
KyferEz is offline KyferEz  United States
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Where are you buying them from?

At 1000 qty they are $0.74 at mouser. Digikey has 640N for $1.47 or 640PBF for $0.58.
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Old 16th June 2007, 10:09 PM   #6
Tom7227 is offline Tom7227  United States
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Perhaps the question is not beta matching,

BUT, what is the characteristic change with a "leaded" vs NON leaded semiconducter?
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Old 16th June 2007, 10:19 PM   #7
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The difference is not lead or lead-free at all, the N suffix is simply a later replacement using newer technology to achieve a smaller die size. Hence the N suffix cannot take as much power when used in linear mode.

There is a document on the IR website that explains it all.
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