A very nice looking SIT-ish Mosfet - diyAudio
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Old 9th February 2017, 09:39 AM   #1
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Default A very nice looking SIT-ish Mosfet

http://www.infineon.com/dgdl/irfps38...53562ce01f2035

It has the same kind of Triode transfer-curves as the SIT Nelson Pass presents in his Introduction to Static Induction Transistors article:http://www.firstwatt.com/pdf/art_sit_intro.pdf

With a low 0.5 C/W total thermal resistance, 100 volt drain to source rating and 580 watt power rating, it should be very suitable for a nice sounding single ended amp.

Cheers,
Johannes
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Old 9th February 2017, 12:03 PM   #2
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Interesting. Any plans for a build?
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Old 9th February 2017, 02:46 PM   #3
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The same kind of triode curves
Maybe with schade feedback can be....
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Old 9th February 2017, 04:05 PM   #4
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"Pentode" example.
What is very nice looking that your taste and diy & experiments are funny.
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Old 9th February 2017, 04:16 PM   #5
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Are you finding these by trial and error or finding them as they come on line?

Has anyone simply just asked the transistor manufacturers if they had any existing jfets or mosfets with triode curves and/or behave like a SITs? Wouldn't their engineers just know?
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Old 9th February 2017, 07:00 PM   #6
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Quote:
Interesting. Any plans for a build?
I guess simplicity and single ended designs is the key with these devices. A common source with some source-degeneration, 0,22 to 0,5 ohm or so, and a simple power-resistor drain-load should sound marvelous.


Quote:
Are you finding these by trial and error or finding them as they come on line?
Mostly trial and error. The "38" in the name IRFPS3810 caught my attention. I like the IRL3803V and the IRLB3813, and I hoped there was some similarities between them.

Quote:
The same kind of triode curves
Maybe with schade feedback can be....
The main attribute with a SIT or a "triody" device is not that it is a depletion mode device. It is the ohmic behavior, where the current increases with an increase in voltage drain to source without an increase in voltage between gate and source. It is the exponentially rising gain with an increase of voltage over the device.

The IRFP7430 and IRL3803V is not as linear as this IRFPS3810. Their transfer-curves deviates from the ohmic behavior in a non-linear fashion.
Even though I really like the IRFP7430 I believe the IRFPS3810 is a much nicer device in many ways. Less gate-capacitance, much more linear transfer-curves, a much larger Safe operating Area and a much better voltage-rating.

I have been playing a lot with different methods of achieving a Triode charterer by the use of Schade feedback, but it all comes down to the simple fact that even Schade feedback is a kind of global negative feedback. I generally prefer an inherent Triode charcter without the use of global negative feedback. The negative feedback makes everything sound correct and dull like an accountant, even though Schade feedback does this much less then normal global NFB. It sucks the life out of the reproduction of music.

An IRFP7430 breaths life into the reproduction of music (with some aggressive brutality). I hope the IRFPS3810 does so with less distortion then the IRFP7430.
The published transfer-curves indicates this.

Cheers,
Johannes
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Old 9th February 2017, 07:15 PM   #7
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Remember that most of the newer MOSFET are being designed in focus of as lower power waste for be used to switching topologies as they can, not for linear operation.

Salutti.
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Old 9th February 2017, 11:19 PM   #8
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It's local feedback no global.
Made with two resistors but not the only egsisting trick....

Iteresting article how transform ordinary jfet to be triode like :

The Trioderizer - a solid state triode

The same technique is used in tube amplification for pentodes.
Cheers
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Old 10th February 2017, 02:37 AM   #9
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Quote:
Originally Posted by Circlomanen View Post


The main attribute with a SIT or a "triody" device is not that it is a depletion mode device. It is the ohmic behavior, where the current increases with an increase in voltage drain to source without an increase in voltage between gate and source. It is the exponentially rising gain with an increase of voltage over the device.

Cheers,
Johannes
Johannes, i know you've been looking at these for quite some time so permit me an innocent question - the curves suggest that this region only exists at very low VDS - I can't quite get my head round how you get any power out of the device if there's only 1-2 volts across it ?
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Old 10th February 2017, 09:51 AM   #10
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the curves suggest that this region only exists at very low VDS - I can't quite get my head round how you get any power out of the device if there's only 1-2 volts across it ?
irfps3810.JPG

The transfer-curves encircled in red.

Cheers,
Johannes
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