The Miller cap is not added to stop the oscillation, but to
slow the switching edges.? You can see
the edge slow-down effect in the uploaded file (Files/Temp folder).? The simulation has a pair of the circuits,
one with, and one without the 300pF cap that performs the slow-down.? Without the slow-down, there is a 30MHz spike
in the PCB emissions scan, related to the edge rate of the switching
waveform.? By adding the cap, along with
a 47 ohm resistor in series with my gate drive, the slower edge rate lowers the
emissions at that frequency by about 10dB, which is my goal.? Of course, this allows for any high-Q circuit
strays to try to oscillate, which is what I'm trying to simulate.
I've tried your suggestions, but the simulation still shows
no sign of oscillating.??Am I still doing something wrong with my quest for
oscillation?
I've uploaded a version of the file "Oscillating Miller FETs 02.asc" to the files/temp directory.? This file has my interpretation of your suggestions, but I still can't make it oscillate.? I've tried a variety of component values and several different FETs, looking for a hint of oscillation.? Can somebody make it oscillate for me?
thanks,
Carl
