Reverse Power Gain in the Grounded Collector Circuit

Author: Leonard Krugman

The grounded collector connection also has the unique ability to furnish power gain in the reverse direction. This characteristic might be anticipated on the basis of the equivalent circuit, since the internal generator r_mi_e is common to both the input and output circuits, and the values of r_b and r_e are approximately equal. The equivalent circuit for the reverse connection is illustrated in Fig. 4-15. The resulting four-terminal parameters for this connection can be evaluated in terms of the internal transistor parameters as before:

Fig. 4-15. Equivalent "T" for reverse operation of grounded collector connection.

A. 

The input loop equation is:

e₁ + r_mi_e = i₁ (r_e + r_c) + i₂r_c

Substituting i_e = i_l,

e₁ = i₁ (r_e + r_c - r_m) + i₂r_c

when

i₂ = 0, e₁ = i₁ (r_e + r_c - r_m);

then

r₁₁ = r_e + r_c - r_m,

which is equal to r₂₂ in the forward direction.

B.

Using the same input loop equation, when

i₁ = 0, e₁ = i₂r_c,

then

,

which is equal to r₂₁ in the forward direction.

C.

The output loop equation is

e₂ + r_mi_e = i₁r_c + i₂ (r_b + r_c);

Since

i_e = i₁, e₂ = i₁ (r_c - r_m) + i₂ (r_b + r_c)

when

i₂ = 0, e₂ = i_x (r_c - r_m);

then

; which is

equal to r₁₂ in the forward direction.

D. 

Using the same output loop equation, when

i₁ = 0, e₂ = i₂ (r_b + r_c);

then

r₂₂ = e₂/i₁ = r_b + r_c,

which is equal to r₁₁ in the forward direction.

Therefore, it can be seen that any of the equations derived for operation in the forward direction can be revised for use in the reverse direction by substituting r₁₁ for r₂₂, r₁₂ for r₂₁, r₂₁ for r₁₂, and r₂₂ for r₁₁. For example, the maximum available power gain in the forward direction, , becomes in the reverse direction.