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Old 4th May 2004, 08:49 AM   #1
guymrob is offline guymrob  Singapore
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Smile What is most linear power Mosfet around?

Hi everyone,

I have a DIY amp based on 2sk1058 and 2sk162 Hitachi power mosfets. In term of linearity how would it compare with other type of audio power mosfets? Are there better mosfets around?Thanks for your feedback.

Guy
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Old 4th May 2004, 04:54 PM   #2
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It depends on the application. If there were such a thing as
the ideal Mosfet for all linear applications, then everybody
would be using it, and it would become cheap through high
volume.
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Old 4th May 2004, 08:48 PM   #3
Pabo is offline Pabo  Sweden
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If you are talking about output stage MOSFETs I would go for parts with a low gate to source voltage variation related to drain source variations and drain current variations. I suppose that a large MOSFET chip will give you a high Ids/Vgs but I am not sure how Vgs will respond to Vds-variations. The are allways cascodes if you want to keep the voltage drop constant over the transistors
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Old 4th May 2004, 09:08 PM   #4
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That would be a Vertical Mosfet. The other kind is a Lateral,
which has lower transconductance, but also lower Capacitance
Gate-Drain. There are proponents of both types. Charles
Hanson argues for Laterals, I tend to use Verticals, and to
deal with the G-D capacitance, I too would recommend
cascoding.
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Old 4th May 2004, 11:11 PM   #5
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Default Re: What is most linear power Mosfet around?

Quote:
Originally posted by guymrob
Hi everyone,

I have a DIY amp based on 2sk1058 and 2sk162 Hitachi power mosfets. In term of linearity how would it compare with other type of audio power mosfets? Are there better mosfets around?Thanks for your feedback.

Guy
I don't know how you would define "better mosfets". There is good news and bad news about these devices, as with most electronic components, and you must make your best judgement call in your design.

These are called "lateral" power MOSFETs, and have much lower transconductance and higher on resistance than typical "vertical" power MOSFETs (that's the bad news). The good news is they can be easily paralleled for higher output, and they need simpler biasing (minimal temperature compensation needed). Unfortunately, they are not well suited for the vast majority of other MOSFET applications, so they have become low volume, high-priced components, compared to vertical MOSFETs.

The advantages of vertical MOSFETs have led them to dominate the market. In fact, there are literally thousands of vertical MOSFETs made, and only a handful of lateral parts available today. The laterals are primarily aimed at the high end audio amplifier market for new design. and replacement market for existing products.

With care in design, the disadvantages of vertical MOSFETs can be largely nullified. Biasing must be temperature compensated. If used in parallel, they must be carefully matched for Vgs(on) and transconductance, and used with large matched source resistors; they should be derated because the sharing will never be perfect.

In your particular design, there are only two other lateral MOSFET device pairs that might be "better": the 2SJ352/2SK2221 pair and the 2SJ201/2SK1530 pair. [I'm ignoring boutique semiconductor vendors, since their parts are hard to get and expensive.] These are rated for slightly higher current and voltage. If you don't need that, I would not bother to change the design.
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Old 5th May 2004, 01:41 AM   #6
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Actually, the Toshiba 2SJ201/2SK1530 pair are vertical devices with all of the advantages and disadvantages thereof. One nice thing about this pair is that the threshold voltage is lower than found in many vertical devices. Another nice thing is that they are good complements to each other, unlike the hit-and-miss approach you're stuck with for American vertical MOSFETs. (But I'll still stick with laterals.)
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Old 5th May 2004, 07:36 AM   #7
mandat is offline mandat  Poland
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The best and the most complementary MOSFETs for audio purposes come from EXICON. Such opinion is delivered by polish manufacturer of High End amps.
http://www.profusionplc.com/product-frame.htm
click EXICON
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Old 5th May 2004, 02:51 PM   #8
zinsula is offline zinsula  Switzerland
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Default EXICON

Quite interesting...
But the prices are also pretty high....

BTW-has anyone bought the EXICON Audio evaluation board? There was a thread here in 2001 about this, but i don't know if eventually someone bought that.

Regards
Tino
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Old 5th May 2004, 03:51 PM   #9
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Default Re: EXICON

Quote:
Originally posted by zinsula

But the prices are also pretty high....

Exicon expensive??? Maybe there are countries where you
can buy the Hitachi devices much cheaper, but here in Sweden
at least they cost around three times the price of the Exicons.
(Yes, one has to order Exicon from the UK, but since they don't
charge for shipping, have no minimum order size and there are
no customs fees within EU, it is fair to compare with swedish
off-the-shelf prices). I have seen lower prices for the Hitachis
elsewhere, but they are still more expensive than Exicon.
Further, the Exicons are slightly higher rated for max Id.
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Old 5th May 2004, 04:47 PM   #10
EUVL is offline EUVL  Europe
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Default Exicon vs Hitachi

You can get 2SK1058 in Germany for under 6 Euro (= 4 GBP). I know at least 2 sources, one of which is Reichelt.

And if you look at the datasheet from Exicon, I wouldn't consider them linear at all, especially if you bias them at around 1 to 1.5A. They might be a bit better at 3A, but then you have to cascode to get the heat down.

Compare to the few 2SK1058's and the 2SK1529's that I have measured, I'll rather stick to the Japanese. But if you can live with second harmonics (e.g. drive them 180 deg out of phase like in JLH 10W), IRFP is unbeatable for price.


Patrick
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