How about using a 15 V Zener instead of a hot-carrier diode?
I think that the gate of the HV MOSFET should be grounded for AC.
So in the end we have what the name of the thread says: A grounded-gate
MOSFET
:-).
A grounded-base bipolar has good high-frequency properties. I wonder if
this is
the case for power MOSFETS. Probably.
Some MOSFETS (IRFP 460 for instance) have impressive capabilities: 500
V, 20 A,
but very large turn-on (150 ns) and turn-off times (180 ns), which makes
them
unsuitable even for a 40-meter amplifier.
Maybe they could be usable with this cascode circuit. I wonder if
someone has already tried this.
Vy 73 de Angel Vilaseca HB9SLV
Tomm Aldridge wrote:
> Yes, except the 15V supply is established with respect to the source.
> As I said, I have built the version with a bipolar on the top which was
> emitter switched by the FET on the bottom of the pair. W/ proportional
> drive on teh bipolar, it was fast and efficient.
>
> Angel Vilaseca wrote:
>
> > You mean something like this?
> >
> > See schematic attached
> >
> > 73 de Angel Vilaseca HB9SLV
> >
> > Tomm Aldridge wrote:
> >
> >
> >>I have designed and built cascode hybrids made from a HV bipolar and a
> >>LV IR MOSFET device. Ther work very well. No reason a FET - FET should
> >>not work as well or better. It would be imperative to keep the gate to
> >>source voltage within safe operating limits of course.
> >>
> >>Radio WC6W wrote:
> >>
> >>
> >>>On Fri, 14 May 2004 11:23:42 +0200 Angel Vilaseca <avilaseca@bluewin.ch>
> >>>writes:
> >>>
> >>>
> >>>>Hi,
> >>>>
> >>>
> >>> <snip>
> >>>
> >>>>My question is: Could a gate-grounded circuit help with the
> >>>>power-MOSFET
> >>>>input matching problem?
> >>>>
> >>>>More generally: Has someone already tried to build a grounded-gate
> >>>>power MOSFET amplifier?
> >>>>
> >>>>
> >>>>
> >>>>Angel Vilaseca HB9SLV
> >>>>
> >>>>
> >>>
> >>>
> >>>Hi Angel,
> >>> You would still have the horrific input capacitance in GG and an even
> >>>lower impedance to drive.
> >>>
> >>> I've been contemplating a cascode connection to alleviate the input
> >>>capacitance using a low voltage (25V) FET for the input device connected
> >>>to a 500V FET, with the gate biased to 15V or so, to complete the
> >>>cascode.
> >>>
> >>> The low voltage input FET has 1/10 or so of the capacitance of the HV
> >>>part. If the HV FET's have a 200V Drain supply the output impedance will
> >>>be in the vicinity of 50 ohms which will be easier to match to the load
> >>>than a typical transistor circuit.
> >>>
> >>> I've seen cascodes of similar design used for driving CRT's and other
> >>>things but, never for RF power. There may, or may not, be a reason why
> >>>not... :-)
> >>>
> >>>73 & Good morning,
> >>> Marv WC6W
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>*
> >>>
> >>>
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