Attached is the snapshot of the circuit I am working with.

[![enter image description here](https://i.stack.imgur.com/GL8QF.jpg)](https://i.stack.imgur.com/GL8QF.jpg)

My aim is to find the minimum input voltage to turn on the transistor (T)

With the following assumption, voltage drop across the resistor R1 is very small,

Vin > 2.7V + 0.6V ( Zener voltage + drop across V\_BE)

That is, minimum input voltage should be minimum of 3.3V to turn on the transistor (T).

**Questions**

1. Can someone verify the calculation?
2. How will calculation changes if drop across R1 also need incorporate?