The series-pass unit operates in the linear mode, which means that the unit
is not designed to operate in the full on or off mode but instead operates in a
degree of “partially on.” The negative feedback loop determines the degree of
conductivity the pass unit should assume to maintain the output voltage.
The heart of the negative feedback loop is a high-gain operational amplifier
called a voltage error amplifier. Its purpose is to continuously compare the dif-
ference between a very stable voltage reference and the output voltage. If the
output differs by mere millivolts, then a correction to the pass unit’s conductiv-
ity is made. A stable voltage reference ...
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