Voltage divider bias:
The voltage divider is made by using external resistors R1 and R2. The voltage beyond than R2 forward biases the emitter junction. Via proper selection of resistors R1 and R2, the operating point of the transistor can be prepared independent of β. In this type of circuit, the voltage divider holds the base voltage fixed independent of base current given by the divider current is large as compared to the base current. Though, even with a fixed base voltage, collector current changes with temperature thus an emitter resistor is added to stabilize the Q-point, identical to the above circuits with emitter resistor.
In this circuit the base voltage is provided by:
VB = voltage across R2
= Vcc (R2) / (R1+R2) - IB (R1R2) / (R1+R2)
≈ Vcc (R2) / (R1+R2) provided IB << I2 = VB /R2
VB = Vbe + IERE
For the given circuit,