From: K S <kresho@gmail.com>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Sat, 14 Aug 2021 05:48:13 -0700
Subject: Re: [EE] Tek DSO display issue?
Thread-Topic: [EE] Tek DSO display issue?
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Thank you for the response.

> What FET are you using ?
> supply? The falling edge looks to have a bit of a slope to it. Also, chec=
k

I picked a FDD86367 to start but then tried with a few others. I'm a
bit unhappy about those lengthy switching times but I don't see much
space to move. The Qg for the FDD86367 is 68nC which is pretty low. No
gate resistance but I did try 10R with little change. I've got the
high speed current paths as short as possible - I even cut and shut
the inductor directly to minimise some PCB traces but didn't see any
improvement.


> Your second photo may be showing  artifacts of overloading the front end =
of
> the scope (in the 2V range).

Yes, indeed I think this is the issue. Today I put a 10K-10K divider
across D and S and measured at the half point rather than across DS.
The scope started "playing up" and curving the edges at 0.5V/div. I am
now pretty sure that the waveform clipped from the top of the scope
display is not a don't care - it does seem to saturate the input
circuits. I must say this has never caught me out with this scope in 2
decades!
--=20
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