Linear power supplies are more expensive because larger capacitors and transformers are needed for power voltage conversion at 60 Hz, the power line, and AC mains frequency. Therefore, linear supplies are limited to precision supplies in which the switching noise is a problem and small supplies where a switching regulator is deemed too complicated. The linear supply shown on this slide is a simple linear power supply. The 120V AC input voltage is stepped down to 12.6V AC by an input transformer as shown by the ±17.8V sinewave at the top and labeled “Secondary AC Signal.”  If the 200 µF filter capacitor were not in the circuit, the fullwave rectified signal across the resistor load would be the zero to 16.4V varying DC voltage shown. If the capacitor is put in the circuit as shown, it filters the voltage and smoothes it to about 16V DC voltage with a couple of volts of ripple voltage on it. The ripple voltage causes ripple current to flow in the capacitor. With the capacitor in the circuit, the rectifying diodes only conduct when the load causes the voltage to dip low enough to be less than the 120V AC input voltage. Thus the diodes only conduct at the peaks of the AC input voltage.