DC Equivalent Circuit of Transistor:

DC Equivalent Circuit of Transistor – In the common base circuit, the emitter diode acts like a forward biased ideal diode, while collector diode acts as a current source because of transistor action.

Thus an ideal transistor in common-base configuration can be considered as a rectifier diode in the emitter circuit and current source in the collector circuit, as illustrated in Figs. 10.72(a) and 10.72(b).

In the common emitter configuration, the ideal transistor may be considered as a rectifier diode in the base circuit and a current source in the collector circuit, as shown in Figs. 10.73(a) and 10.73(b).

In the common collector configuration, the ideal transistor may be considered as a rectifier diode in the base circuit and a current source in the emitter circuit, as illustrated in Figs. 10.74(a) and 10.74(b).

Note : In the current source, the direction of arrow indicates the direction of conventional current.