Mp8008 vin voltage

hi.

I have a question while looking at the EV8008 document.
vin = Flyback controller input supply.
VDD : 37~57V / VIN : 0~35V

EV8008, transformer aux and VDD are entered into the VIN via Transistor(Q4).
If VDD is entered in VIN , it is out of the VIN range.

I don’t understand this part.
please explain to me

Thank you

Hi seungyeon.won,

That is part of the voltage clamping circuit. This will clamp VDD to fit within the range of Vin.

Regards,
Vinh Tran

Q4 BASE Voltage limit !
Isn’t vdd into vin without limit?