RE: [TCML] SSTC opinions solicited

[<sparks@xxxxxxxxxxxxxx>]

> I'm using 6, STE40NK90ZD 40A/900V MOSFETs in a ring configuration.

Those are nice transistors, but you do pay a lot for the convenience of
screw terminal connections and an electrically isolated mounting design.

I'd be more inclined to use something like the more common
HGTG18N120BND, which is available for about $2.00.  One of these is a
pretty fair substitute for the STE's, except for the power dissipation.
390 vs. 600 watts.  You could easily parallel two of the HGTG18N120BND's
and have higher dissipation and less driving power requirements. They
are also have a faster rise and fall time than the STE's.

When I use then in high power circuits, I usually bolt them directly to
the heat sink with no thermal pads.  Of course, the heat sinks have to
be electrically insulated, but the transistors sure like it that way.

And yes, I have popped a lot of transistors while designing new gadgets.
I think that's par for the course.  If you don't vaporize a few, you
really don't know what the circuit limits are.  The latest "Oops!!" for
me was a pair of $58.00 RF power transistors.  Which sort of ticks me
off, since they go in a used RF amplifier that only cost me $125 in the
first place!

73,

Ralph   W5JGV - WD2XSH/7

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