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Old 25th March 2014, 07:07 PM   #1
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Default F5T Mosfet options

I've been reading up on the F5T for a few weeks now, hunting around the forums and finding most of the answers I've needed. The one thing that keeps tripping me up is the output Mosfets, because the original Fairchild components specced by Mr. Pass are only available in bulk from suppliers such as Rochester and Harry Krantz.

I saw the FQA36P15 and FQA28N15 mentioned on a thread from a few years back with very little follow-up. They are slightly different from the FQA16N25 and FQA12P20, with lower Vdss and higher Id. They also have a significantly higher typical Crss of 110pF, which Fairchild still considers to be "low."

I'm wondering if anyone has had the opportunity to compare these devices with a curve tracer to see if they exhibit similar characteristics, as they are much easier to come by than their Pass-approved equivalents. If not, what are the current alternatives being used? I've heard of Toshiba parts with lower Id being used, but I'm not familiar with their model numbers or characteristics in comparison.

Thanks,
Josh

(Originally posted this in the SS section by mistake)
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Old 25th March 2014, 08:08 PM   #2
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Have your look at the Mouser and Dig-key web sites?

FQA36P15 Fairchild Semiconductor | Mouser

FQA28N15 Fairchild Semiconductor | Mouser

FQA16N25 Fairchild Semiconductor | Mouser Obsolete

FQA12P20 Fairchild Semiconductor | Mouser Obsolete
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Old 25th March 2014, 10:29 PM   #3
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Yes I took a brief look at the datasheets, and the curves are not quite the same, but I'm just wondering if anyone's used them with any sort of success, or deemed them too different to work without major rework of the schematic.
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Old 25th March 2014, 11:51 PM   #4
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is there a problem obtaining IRFP in USA ?
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Old 26th March 2014, 01:04 AM   #5
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I wouldn't worry too much about curves.
Feedback takes care of any none linearities.

I have used irfp240/9240 which are quite different devices with some success.
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Old 26th March 2014, 11:18 AM   #6
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Quote:
Originally Posted by Zen Mod View Post
is there a problem obtaining IRFP in USA ?
Probably not a problem obtaining them but a problem with the P-channel defect:
John Curl's Blowtorch preamplifier part II
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Old 26th March 2014, 11:27 AM   #7
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besides being blind , I'm also deaf , so I'm not finding that as defect
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Old 26th March 2014, 11:43 AM   #8
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To be clear, IRFP does not have any "Defect". The "P" in IRFP stands for plastic as in TO-3P.
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Old 26th March 2014, 12:14 PM   #9
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I remember NP mentioning that the IR version of the IRFP9240 had a glitch in its transfer function that was audible, but not so bad and the parts are usable. These are the parts that are currently available. Fairchild's version of the same part did not have that glitch. I am running out of my stock of the original Fairchild parts, but that means I am building amps.

Last edited by BobEllis; 26th March 2014 at 12:19 PM.
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Old 26th March 2014, 12:26 PM   #10
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Yeah, Papa commented on it in the BA2 article, in the distortion vs frequency section:

Burning Amplifier BA-2

He also discussed it in the testing mosfet article I believe.
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