Why Figure E7-2 shows a series pass transistor with its base held at a fixed reference by a zener diode and dropping resistor, with the load taken from the emitter. The transistor conducts continuously and drops the difference between input and output voltage as heat, so the output sits about one base-emitter drop (0.7 V) below the zener voltage. Continuous conduction with no switching element is the definition of a linear regulator.