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# 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 rmie is common to both the input and output circuits, and the values of rb and re 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 + rmie = i1 (re + rc) + i2rc

Substituting ie = il,

e1 = i1 (re + rc - rm) + i2rc

when

i2 = 0, e1 = i1 (re + rc - rm);

then

r11 = re + rc - rm,

which is equal to r22 in the forward direction.

B.

Using the same input loop equation, when

i1 = 0, e1 = i2rc,

then

,

which is equal to r21 in the forward direction.

C.

The output loop equation is

e2 + rmie = i1rc + i2 (rb + rc);

Since

ie = i1, e2 = i1 (rc - rm) + i2 (rb + rc)

when

i2 = 0, e2 = ix (rc - rm);

then

; which is

equal to r12 in the forward direction.

D.

Using the same output loop equation, when

i1 = 0, e2 = i2 (rb + rc);

then

r22 = e2/i1 = rb + rc,

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.

Last Update: 2010-11-17