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<div class="moz-cite-prefix">Hi Tom,<br>
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<div class="moz-cite-prefix">On 08.05.2020 20:47, Tom Corbitt wrote:<br>
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<blockquote type="cite"
cite="mid:CAGH9ZXPpnAnnY-a-aDRVEg4s5yWM=p+kho1ac0nqeqnHmrBPFA@mail.gmail.com">
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<div dir="ltr">So my daughters lamp failed the other day and I
opened it up to discover it was much more complicated than I
imagined it to be. Inside. along with a Holtek 8 bit micro was
the awesomely named VIPER12A; a google search shows it to be the
brains of a switching power supply circuit
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<div><a
href="https://www.st.com/resource/en/datasheet/viper12a-e.pdf"
moz-do-not-send="true">https://www.st.com/resource/en/datasheet/viper12a-e.pdf</a> <br>
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<div>My question relates to the 4th connection shown in the
block diagram on page one (and later in the technical
explanation) Just what the heck is the bottom element shown
on the FET? (the lowest element under what I'd call the
traditional source elements?) Is it the body? Looking at
wikipedia I see that the source can have a source connected
to a P type island (which I guess is connected to the
substrate?)</div>
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<div><img src="cid:part2.B8DF6C58.97E7A61A@schmitzbits.de"
alt="image.png" class="" width="514" height="258"><br>
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<div>What makes it odder to me is in figure 5 they show a
constant current source "Is" which they say is proportional to
the current flow across the fet (Id)<br>
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<p>It is a second source terminal. It is there to create a "tap" of
the drain to source current. Most likely with a smaller geometry
to the other "source", i.e. its so that only a fraction of the
current flows through it. <br>
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<p>This is easier to realize in a chip than a shunt resistor to
measure the current. <br>
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<blockquote type="cite"
cite="mid:CAGH9ZXPpnAnnY-a-aDRVEg4s5yWM=p+kho1ac0nqeqnHmrBPFA@mail.gmail.com">
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Is this a special feature made/incorporated into this specific
FET or is this something that you can do with proper biasing
of the body? <br>
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<p>Yes, this is done on the die/chip level.<br>
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<p>It is probably not connected to the body, as that would short it
to the other source terminal.</p>
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<p>Best,</p>
<p> René<br>
</p>
<pre class="moz-signature" cols="72">--
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