Transistor Hybrid model:-

Make Use of h - parameters to explain a transistor have the following benefits.

a)      h - Parameters are real numbers that are up to radio frequencies.

b)      They are simple to measure

c)      They can be ascertained from the transistor static characteristics curves.

d)      They are suitable to use in circuit analysis and design.

e)      Simply convert able from one configuration to other.

f)       Readily supplied through manufactories.

Figure: CE Transistor Circuit

To obtain the Hybrid model for transistor consider the CE circuit displayed in figure. The variables are i_B, i_c, v_B(=v_BE) and v_c(=v_CE). i_B and v_c are considered as a independent variables.

Then,

v_B= f₁(i_B, v_c )    ----------------------(1)                                    

i_C= f₂(i_B, v_c )    ----------------------(2)

By making a Taylor's series expansion around the quiescent point I_B, V_C and neglecting higher order terms, the following two equations are acquired.

Δv_B = (∂f₁/∂i_B)V_c . Δ i_B + (∂f₁/∂v_c) I_B. Δv_C --------------- (3)

Δ i_C = (∂f₂/∂i_B)V_c . Δ i_B + (∂f₂/∂v_c) I_B. Δv_C ---------------- (4)