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.