Sweep VBE and VCE to visualise BJT operating regions; explore voltage-divider Q-point bias
A BJT is a current-controlled device: small base current IB controls much larger collector current IC. β (hFE) = IC/IB, typically 50–300, varies with temperature and operating point.
Cutoff: VBE < 0.6V, transistor off. Active: VBE ≈ 0.7V, IC = β×IB — amplifier region. Saturation: both junctions forward-biased, transistor fully on, VCE(sat) ≈ 0.2V.
Voltage-divider bias sets the Q-point using a resistor divider at the base, independent of β. If the divider current is ≥ 10×IB, the Q-point is stable across transistor variations and temperature.