Confusin on BJT Small-Signal Model (Hybrid-Pi)

[KingNothing]

I'm confused about how exactly the output resistance and other resistances are set up in the small signal model. Is this small signal model correct? Please regard underscores as a subscript. Is r_0 always connected between collector and emitter?

 

[dlgoff]

Hello KingNothing

Your model doesn't look like what I remember, so I did a little search and found this site that has a similar model for equivalent circuits modified to incorporate Early effect. And yes, the output resistance would be across the collector and emitter.
http://people.seas.harvard.edu/~jones/es154/lectures/lecture_3/bjt_models/bjt_models.html"

 

[oswaler]

The small-signal model, also known as the hybrid-pi model, is a simplified representation of a bipolar junction transistor (BJT) that is commonly used in circuit analysis. In this model, the BJT is divided into three regions: the base, the collector, and the emitter. The output resistance, also known as r_0, is a parameter that represents the resistance seen at the collector terminal when a small AC signal is applied at the base terminal.

In the small-signal model, r_0 is typically connected between the collector and the emitter. This is because r_0 represents the resistance of the collector-emitter junction, which is the primary output of the BJT. However, in some cases, r_0 may also be connected between the collector and the base. This depends on the specific circuit configuration and the assumptions made in the model.

It is important to note that the small-signal model is an approximation and may not accurately represent the behavior of the BJT in all situations. It is best to consult the datasheet or conduct experiments to determine the exact values of the parameters for a specific BJT in a given circuit.

In summary, the small-signal model is a useful tool for analyzing BJT circuits, but it is important to understand the assumptions and limitations of this model. It is always a good practice to verify the model's accuracy through experimentation or by consulting reliable sources.