Please refer to DC1317A eval board schematic, Please let me know the purpose of Q10 (PBSS8110). Here i am attaching schematic also. I am not able to understand purpose of this circuit. Please calrify this.
The Q10 provides 9.3V bias voltage Vu1 that allows controller to start running. Once the output is in regulation the controller bias will come from L2. The voltage coming from L2 will lift emitter of Q10 and turn Q10 off. Using this circuit allows for fast startup and highest efficiency.