A guide of transistor

For an nPn transistor, a transistor is biased (turned on) when the input signal (Vin) is greater than the baseemitter voltage (Vbe) of 700 mV. The mathematical expression for the electrical relation of Vin to Vbe is Vin > Vbe.

For a PnP transistor, a transistor is biased (turned on) when the Vin is less than the Vbe of 700 mV. The expression for the electrical relation of Vin to Vbe is Vin < Vbe.