SATURATION

If IB continues to rise, a point is reached eventually where IC increases less rapidly. Ultimately, the IC versus IB function, or characteristic curve, of the transistor levels off. The graph in Fig. 16-8 shows a family of characteristic curves for a hypothetical bipolar transistor. The actual current values depend on the particular type of device; values are larger for power transistors and smaller for weak-signal transistors. Where the curves level off, the transistor is in a state of saturation. Under these conditions, the transistor loses its ability to efficiently amplify signals. However, the transistor can still work for switching purposes.

Fig. 1. A family of characteristic curves for a hypothetical npn bipolar transistor.