Zener diode regulator with transistor
I am trying to analyze the effect of varying V1 on the circuit voltages and currents,


Until the zener starts to conduct, it appears as a high resistance device and Vb = V1. So the output voltage Ve = Vb - Vbe = V1 - 0.7v.

Once the zener starts to conduct, it clamps Vb to its reverse voltage Vz, so Ve = Vb - Vbe = Vz - 0.7v.