Main parameters of transistor 3

Namely, β=△ Ic/△ I (B)

The above two parameters respectively indicate the amplification ability of the transistor for DC current and AC current. However, since these two parameter values are approximately equal, i.e. β ≈ β, they are generally not distinguished in practical use. Due to the production process, even pipes produced in the same batch have different beta values. For convenience and practicality, manufacturers sometimes mark the beta value on the transistor for users to choose from.

(4) The characteristic frequency product decreases with the increase of operating frequency, and the higher the frequency, the more severe the decrease in β. The characteristic frequency light of a transistor refers to the frequency value at which the body value drops to 1. That is to say, the transistor operating at this frequency has lost its amplification ability, and f (T) is the limit frequency of the transistor in use. Therefore, when selecting a transistor, the characteristic frequency of the transistor is generally at least three times higher than the operating frequency of the circuit. But it's not that the higher f (T), the better. If you choose too high, it will cause oscillation in the circuit.