**Level:** transistor beginner (sorry for that)

**Question:** is a resistance R1 110 Kohms the good one to put before the b branche of a PN2222 transistor, if we want this transistor being in switching mode when the 0 to 30 volts variable voltage coming into the circuit is above 18 volts, and make the LED lighting above 18 volts ?

**Image of the circuit:**
![circuit][1]
I put a green led in the circuit

**Data**:
PN2222 transistor data: beta=300; Vce_sat 1=1; Vbe_sat=2; Vce_max=30
LED: Ic=Iled=0,025 A; Uled=2V (green led)
R led= 600 ohms (Vcc-Vce_sat-Uled, with Vcc at 18 volts)
Source of tension: from 0 to 30 volts
Tension where the transistor should light the LED and let the electricity running (contact between c and e): 18 volts

**calcul done**
As:
Vcc = Vce + Urel,
Vce = Vce_sat,
Urel = Rrel x Ic,
Vcc = Vce_sat + Rrel x Ic <=> Ic = (Vcc - Vce_sat) / Rrel
Then, for Vcc = 18 volts: Ic = (18-1)/600=0,0283 A

And as:
Ib_min = Ic / ß 
Then, for Vcc = 18 volts, and beta = 300,
Ib_min = 0,0283 / 300 = 0,000094 A

Lets apply a 1.5 security coefficient to get ib_sat
Ib_sat = Ib_min x 1.5 = 0,000094 x 1,5 = 0,00015 A

Then, as:
Ve = Ur + Vbe,
Vbe = Vbe_sat,
Ve = R x Ib_sat + Vbe_sat,
so R = (Ve - Vbe_sat) / Ib_sat
which gives for Vcc = 18 volts:
R = (18 – 2 ) / 0,00015 = 110212 Ohms

Is it the correct value for R to light the LED when the variable tension reach 18 volts ?
  [1]: https://i.sstatic.net/sf0E5.jpg