This is a voltage regulator circuit built based FET KP103K. The FET VT3 acts as a dynamic load for the transistor VT2. Because of this factor increases the voltage regulation: when the input voltage from 11 to 19 V output voltage varies within ± 60 mV. Rated output voltage using Zener type D814B is 9 V.
Voltage Regulator with FET KP103K circuit source: Voltage Regulator with FET