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Re: LF: push/pull

To: [email protected]
Subject: Re: LF: push/pull
From: "Rik Strobbe" <[email protected]>
Date: Tue, 14 Jan 2003 14:30:10 +0100
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Hello Uwe,

power-FETs do have rather large gate-source capacitances that can differ from FET to FET. For the popular IRF450 Cgs is about 2nF, variations between FET's can easily be a few 100pF. If the FETs are driven from a rather high-Z source the variations in Cgs might cause a phase shift, although 10 degrees look very much to me. How did you measure this phase shift ? In the past I have noticed that measuring waveforms at the gate of a FET with the drain open can give very strange results ...
73, Rik  ON7YD

Hi all,

guess many of you built the G0MRF-Quarter-Kilowatt-Amplifier.
I did. the PSU is not finished yet.

got some trouble with the phase of the 137kHz sines
(es triangular and rectangular) measured at the gates of the MOSFETs.
there is a diff btwn the two channels of estimated 10degr.
that means parasitic oscillation if operating the PA, doesn`t it.

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