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Old 22nd January 2005, 08:49 PM   #1
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Default recommendations for mosfets?

this is what i need:

a mosfet that will have a high input impedance of 47K-100K and little HF roll-off.. so low input cap... and be able to handle a 2.5K load as a source follower

another mosfet that will have low input impedance of 10k and little HF roll-off and be able to handle a 250 ohm load as a source follower.

both will be run from a 12v source. unsure yet what mA i will run at.

Thanks!!!
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Old 22nd January 2005, 09:43 PM   #2
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VN10KM and IRF610?
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Old 22nd January 2005, 09:54 PM   #3
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Default VN??

who makes the VN part??
any models for these?
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Old 23rd January 2005, 03:35 AM   #4
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http://www.supertex.com/products/selector_guides/102

How about a J-fet that can really slam?

Idss up to 300mA!

They don't cost a lot, and Mouser sells them.

http://www.supertex.com/pdf/app_notes/AN-D16.pdf
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Old 23rd January 2005, 05:08 AM   #5
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Default Re: recommendations for mosfets?

Quote:
Originally posted by AudioGeek
a mosfet that will have a high input impedance of 47K-100K and little HF roll-off.. so low input cap... and be able to handle a 2.5K load as a source follower

another mosfet that will have low input impedance of 10k and little HF roll-off and be able to handle a 250 ohm load as a source follower.
An IRF610 will actually do both of those, and as many parts as I
try, I tend to keep coming back to it.

If you want to try for high input Z in the first case, check out the
Zetex parts, like the ZVN3310, but check out the noise figure first,
or consider a JFET like a 2SK170.

12 V seems low for linear applications - they really like the
higher voltages. You might consider some Bipolars as a
possibility.
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Old 23rd January 2005, 05:29 AM   #6
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Default Hitachi MOSFET's are back

I saw Hitachi's new web site with their new name - Renesas .
Their MOSFET line is back in production . However I don't know when they started and if they are already available in the market.
Check it out. Can't find the URL now. Do a Google and you should find it. Look for Renesas semiconductors. The parts are not marked Hitachi , they are marked Renesas .
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Old 23rd January 2005, 06:31 AM   #7
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http://www.renesas.com/
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Old 24th January 2005, 12:07 AM   #8
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Default hmmm....

well if i am looking for just source followers and less than 10v or so swing...

what PS voltage should I be using?

24,36??

Also should I use JFETS, BJT's or MOSFETS then?

I like the idea of using the same mosfet in both situations...

maybe the IRF610.... any spice models?

Thanks!!
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Old 24th January 2005, 05:55 AM   #9
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"well if i am looking for just source followers and less than 10v or so swing...

what PS voltage should I be using?"


Well, if you were using a choke as a current source you could get away with as little as 15V or so if the 10V you required was 10V peak.

If you were using a simple resistor as a current source I would use about 100V, that's what McIntosh does.

If you are using an active current source and you only needed 10V peak you might be able to get away with 30V or so.
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Old 24th January 2005, 10:18 PM   #10
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Default how about a

actually am using a step-up 1:3 transformer as the load for the source followers.
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