Re: Low noise mosfet amplifier

Joerg wrote:
Winfield Hill wrote:

One more point, these are high-voltage MOSFETs
we're talking about, and when they're seeing
more than 20 to 25V drain-source. I haven't
seen the problem with say, 55V parts.

Question: What are your favorite HV-FETs du jour? I mean the range
of 800V plus. Finally I got the SPICE files from Infineon for their
SPD06N80 and its brethren. It's a bit like pulling teeth but this time I
received an answer within a week. Still waiting for another one from a
couple years ago ;-)

I have about 30 parts in my inventory that I cycle among,
depending on the task. Most of them have 1000 to 1200V
ratings. I usually use as small a part as possible, to keep
the capacitance down. The IRFBF20 is one part I use,
having purchased 100 some years back (small-die high-
voltage MOSFETs all-too-often become discontinued,
and lifetime buys are one tool to combat that problem).

Last year we made 160 amplifiers, each of which had
six 1.2kV MOSFETs (in series), I used Fairchild's
FQD2N100 in that design. Right now I'm working with
an elegant 1.5kV part by ST, the STP4N150.

But that's not to say I don't have a good collection of 600
and 800V MOSFETs. There certainly are plenty of nice
ones to chose from in that region. Some would make
good choices for fast 600-volt 50-ohm pulse generators,
but in those designs I often end up with 12A 1kV parts.

While we are at it, any hot leads on BJT? Do you think there is a chance
the BUX85 might stick around another 10 years or so?

Sorry, I'm not much of a fan of large, slow, low-beta
high-voltage BJTs. I know they can be very useful in
fluorescent ballast designs, etc. I suppose the days
of color-TV HOTs are coming to an end, and obscure
companies, like Wing Shing Computer Components
in Hong Kong, making the 1.5kV 2SD870, etc., will
have to find something else to make. I see they're
selling NiMH battery packs and bluetooth headsets!
.

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