Tube Miller Effects

[Ray Mack]

Doug:
        I saw a couple of posts that are close but leave out the
mechanism.

        The Miller effect refers to the apparent increase in grid to
cathode capacitance due to the amplification of the tube when modeling
the amplifier for analysis.

        When engineers model a circuit they take the 3 capacitors of
the tube (Cgk, Cgp, and Cpk) and change them into 2 capacitors.  One
is the input capacitance from grid to cathode and the second is the
output capacitance from plate to cathode.

        The Miller effect comes from the large voltage swing at the
plate and how that feeds current from the plate to the grid.  This
extra current is in the proper phase such that it looks just like the
extra current necessary to charge up a much larger grid to cathode
capacitor.  The Miller capacitance shows up in parallel with the grid
to cathode capacitance.  It is a pain because it is usually much
larger than the inherent grid/cathode cpacitance.

        The Miller effect also shows up in bipolar transistor models
and especially in MOSFET power transistor models.

        I hope that this adds more information.

Ray Mack
WD5IFS
mack at mails.imed.com
Friendswood (Houston), TX




______________________________ Reply Separator _________________________________
Subject: Tube Miller Effects
Author:  "Snowden; Douglas" <DSNOWDEN at NCDC.NOAA.GOV> at mails
Date:    7/10/97 6:09 AM


Joe, W7LFF/4 posted a Heath Bulletin (which are very welcome to me) that
referred
to "tube miller effects". I vaguely remember reading this in the past..
Someone
refresh my (and others) mind on what this is please


Doug N4IJ
.