This circuit acts like a zener diode with a wide range of voltages. The current passing via the voltage divider R1-R2 is substantially greater compared to the transistor base current and is in the region of 8 ma.
The stabilizing voltage is adjustable over the range 5-45 V by varying the value of R2. The total current drawn by the Variable zener diode circuit is variable over the range 15 ma to 50 mA. This value is determined by the maximum dissipation of the zener diode. In the case of a 250 mW device, this is of the order of 50 mA.
