Overview of linear power supply operation
The basic design model for a power supply consists
of a control element in series with a rectifier and
load device. Figure 1 shows a simplified schematic
of a series-regulated supply with the phase-con-
trolled pre-regulator depicted as a power switch and
the series element depicted as a variable resistor.
The phase-controlled pre-regulator minimizes the
power dissipated at the series element by maintain-
ing a low and constant voltage drop across the series
element. Feedback control circuits continuously
monitor the output and adjust the series resistance
to maintain a constant output voltage. The variable
resistance series element of the supply shown
in Figure 1 is actually produced by one or more
power transistor operating in the linear (class A)
mode; supplies with this type of regulator are often
called linear power supplies. Linear power supplies
have many advantages. Because they provide suffi-
cient power with stable regulation and little noise,
they usually are the simplest, most effective
solution for providing bench power.