A "grounded gate" of what, Marco?
Not of the IRF510 or any other MOSFET.
The current through the device is determined by the gate voltage.
with a gate at 0v, the current through the device is virtually 100% cut off.
There is no way to get a signal through it.
The gate voltage should be about 3v for signal transfer. However, it inherently
has a high gate capacitance which has to be compensated for at the frequency of interest.
That high capacitance comes from the bigger than averabe size of the die, which is really
designed a lot of current flow in a short period of time (usecs). Operating it linearly
means that we are trying to make it pass a relatively small amount of current (~1-2A)
over a relatively long period of time. The die heats up because of the current flow,
and that has to be controlled.
So there are two problems: we must make a reasonable impedance match to the gate
to allow signal transfer, and we must control the inevitable heat generation from that.
Heat-sinks control the latter. What would you do about the former, i.e., how would you match
the driver transistor to the gate with high capacitance at 40m (or whatever band you choose)?
There is one other problem. The MOSFETS are inherently prone to oscillation because of internal
feedback. Often, it is VHF oscillation and is more or less invisible to the operator. That must also
be controlled. That is both a drive and a layout problem.
john
AD5YE
