On 7/26/2018 10:20 AM, satbeginner wrote:
Hi all,
Bruce, thanks for your addition, for now I only can test "dry", so without the PS actually working, because the FET's and diode's are not here yet.
But I did some measurements on the driver signal driving the gate of the FET (without a FET installed)
The switcher in my scope does free run at 66,5kHz / 15usec, and delivers zero-going OFF-pulses with a 2usec width.
Rise and fall times are about 100nsec each.
I measured the same signals, but now with a 1nF capacitor installed at the G-S pins.
Basically, what I see is that there is no difference in the rise-and-fall times, only the high level (in between the low 2usec pulses) becomes a bit dirty.
But since the FET is switching ON around 3,5V - 4V, the part of the signal that becomes dirty is way beyond the point where the FET switches "ON", so that should not be a problem.
So, my (probably) premature conclusion is: the FET I ordered should work fine.
It's capacity does not have any effect on the rise-and-fall times, it's own turn-on time is way smaller than the applied pulse, and the ON-resistance is lower, so dissipation should be lower.
But, we all know Mr. Murphy (only few people know he actually was an optimist) so -as always- the proof of the pudding will be in the eating....
I took some pictures of the signals and I put them in the album again: /g/TekScopes/album?id=64919&p=pcreated,,,20,1,0,0
To be continued,
Un saludo,
Leo
"I measured the same signals, but now with a 1nF capacitor installed at the G-S pins. Basically, what I see is that there is no difference in the rise-and-fall times,"
I find this somewhat amazing, because when I did the same test, I did see a much larger difference between having the cap in or out.
Unfortunately, I can't pull up any pictures from that time but that was from several years ago and senior memory (84Y) doesn't improve with time.
You might even think about doing a ringing test on the transformer, I've replaced a few of these over the years.
-Bert
