BJT Biasing
Bias configuration
Choose a bias type, enter the supply, transistor and resistor values; the Q-point and region appear live.
Q-point
How to use this calculator
Set the bias configuration (fixed, voltage-divider, or emitter-bias), enter the supply voltage, VBE, β and the resistors, and the calculator solves for the base, collector and emitter currents, the collector-emitter voltage, and the operating region. The voltage-divider uses the Thevenin equivalent VTH = Vcc·R2/(R1+R2), RTH = R1‖R2; fixed and emitter bias use the base resistor directly. All currents assume the transistor is in the active region, which the calculator verifies by checking VCE > VCEsat.
What it means in a real circuit
For a 12 V supply, β = 100, RB = 100 kΩ (fixed bias) the base current is (12−0.7)/100 k ≈ 113 µA, so IC ≈ 11.3 mA and with RC = 2 kΩ, VCE = 12 − 22.6 ≈ −10.6 V — the calculator flags this as **saturation**, telling you the bias is wrong. A voltage-divider bias with R1 = 47 kΩ, R2 = 10 kΩ, RE = 1 kΩ gives VTH ≈ 2 V, IB ≈ 1.7 µA, IC ≈ 170 µA, VCE ≈ 11.4 V — a clean active-region Q-point. Use this to design a bias network, to verify a circuit won't saturate, or to diagnose a transistor that's not amplifying.