The down side of those diodes are, of course non-linear behavior and flat-topping leading to harmonics and splatter. ?I use those on MOSFETS and LDMOS when the parts are very expensive. ?But on these “power supply switch” cheap parts.. not so much. ?
Dr.?William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ
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Big Signal Ranch – K9ZC
Staunton, Illinois
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Villa Grand Piton - J68HZ
Soufriere, St. Lucia W.I.
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On Nov 3, 2023, at 1:09 PM, Steve Beckman <ssteven3sb@...> wrote:
?Farhan, Gordon;
I have back-to-back Zeners from the final FET Gates to Ground on my DE. (No series resistors) Before installing them I tested how well they would clamp at RF frequencies, due to concerns I had about their speed. My tests using a scope and RF at 30 MHz showed that the 5 Watt Zeners I selected did in fact clamp at their design voltage.
The idea is one recommended by W1FB and at least one MACOM spec sheet (MRF275G). I have also come across sources that claim this is a bad idea.
At the time, we were all looking for the cause of final FET failures in the DE. We found low frequency spurious oscillations in the V1, caused by feedback paths in the TR switching circuit, TR Timing problems, excessive drive capability, and excessive low frequency gain. Those issues have since been addressed, reducing if not eliminating the potential for an over-voltage situation at the gates of the final FETs.
I've left the Zeners installed in my DE. As we make progress towards reducing harmonics, spurs, IMD, etc, they may end up getting removed.
73; Steve, N3SB
K9HZ