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Old 19th August 2002, 05:50 AM   #11
tvi is offline tvi  Australia
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I think the Vfets you are discussing use a V shaped stucture, mainly used for RF.

From memory they had a problen with uneven charge buildup in the V channel??

The similar current devices might be the <a href="http://www.onsemi.com/parametrics/selector/0,4093,10201,00.html?LevelName0=Product&LevelName1 =Discrete&LevelName2=Power+MOSFET+%28TMOS%29&Assoc iatedParametrics=Power+MOSFET+%28TMOS%29+10201">TM OS from On Semi</a> or TrenchFET from Vishay/Siliconix.


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James
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Old 20th August 2002, 03:10 AM   #12
BeanZ is offline BeanZ
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VFETS have a solid-state channel structure which is vertically oriented and the lateral MOSFETS have a channel which is....well, lateral. Motorola (ONSEMI) has a series called VMOS which are this type of device. As for the circuit it looks as if it is running open-loop....but that's not giving too much to the cause.

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Old 20th August 2002, 07:39 AM   #13
Tomo is offline Tomo
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Thanks, guys.

I will look into those fets in a few days and come up with something. Hope they have complemental pair of VMOS as they should!

Tomo
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Old 20th August 2002, 08:45 AM   #14
jan.didden is offline jan.didden  Europe
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Default Weird design

The evolution from V fets to the newer lateral or trench types or what have you is the result of the quest for lower Rdson. The downside is that the topology leading to the lower Rdson also increases the capacitances. So, for audio, the Vfet types may well be *better*.

Jan Didden
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Old 20th August 2002, 07:22 PM   #15
Tomo is offline Tomo
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Hey,

I can't find Vfets or Vmos's. I found trench types, but I don't think that is it, right?

Tomo
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Old 21st August 2002, 12:19 AM   #16
Dozuki is offline Dozuki
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I've been working up a circuit that is on this type of vien. Tho, I havn't cascoded the output. I started with a circuit and the idea of building a PP zen type of amp. This didn't work out so well and I gave up when I blew the 540/9540's. I'm not sure these are the easiest critters for this type of topology. There is no thermal compensation that I can see, and the IR's definately seem to need this. I've now started to actually use some Japanese transistors, and low and behold some things are starting to work out. I believe that what I have are VFETs, but alas the differentiation can be hard to sort out at times. I have the Toshiba 2SJ200/ 2SK1529 Comp. Pair. I know that they are not Lateral types, and I presume that they are V types. The spec sheets say that they are for 'high power amplifier'. Anyway point is that I got something in a 2 stage PP to work with these. I substituted in IRF devices once the circuit worked and was not pleased with the results. I suspect that the bias was not correct for the IRF's. And I also suspect this because it seemed to be crossover distortion that I was getting (at least that's what I felt that it was). However, with the toshibas the sound was very similar to that of a Zen circuit but with some audible distortion in the extreeme high end (sounds like > 8K). Anyway, do a Google serch for the original 2SJ/2SK pair and you should find quite a bit of info on them as well as sources if dig hard enough. Hope this is of some help.

-D.
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Old 21st August 2002, 12:19 AM   #17
Nelson Pass is offline Nelson Pass  United States
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For the cascode function you definitely want the
parts with the 4 volt Vgs. As to using the IR type
parts for the gain devices, the 510's already are
fairly low in capacitance, and they are highly
degenerated with the Source resistance, so I
doubt you'll get great improvement with other
Mosfet structures. But then again, it's always
worth trying.
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Old 21st August 2002, 04:27 AM   #18
Tomo is offline Tomo
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Hello,

I think thermal variations can be ignored if I heatsink the fets well. That I indeed will. Am I correct? ... I want to use TO-220AB on-board heatsinks (1.5X1/4X1.5 inch, Identical ones are used for SDS headphone amp.)

Do I have to thermal-couple some components?

So I guess it would work the way it is. Sound quality might be entirely different matter. I will have to see it for myself.

I will try to build it when I have come up with 4 trannies, 2 high current psu and 2 precision ones without cutting into my food budget. (Yeah, I could use Gate's pocket money any day.)

Tomo
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