Power Gain in the Grounded Collector Connection

Author: Leonard Krugman

The operating power gain as defined by equation 3-46 is:

Eq. (4-17)*

In terms of the internal transistor parameters for the grounded collector connection, the voltage gain becomes:

As in the case of the grounded emitter connection, this gain equation is conditional for the point-contact transistor when the stability factor ë is greater than one. The conditional equation is:

(R_g + r₁₁) (R_L + r₂₂) - r₁₂r₂₁ > 0

Substituting the numerical values of the typical point-contact transistor into this equation:

(R_g + 12,000) (R_L - 11,850) + 12,000 (11,900) > 0

The conditional stability characteristic is plotted in Fig. 4-14.

Fig. 4-14. Conditional stability characteristic (grounded collector).

The grounded collector circuit can be stabilized by adding an external resistance R_c. in the collector arm. For example, assume that a resistor R_c = 3,100 ohms is placed in series with r_c. The open-circuit parameters now become:

r₁₁ = r_b + r_c + R_c = 100 + 11,900 + 3,100 = 15,100 ohms

r₁₂ = r_c + R_c- r_m = 11,900 + 3,100 - 23,900 = -8,900 ohms

r₂₁ = r_c + R_c = 11,900 + 3,100 = 15,000 ohms

r₂₂ = r_e + r_c + R_c- r_m = 150 + 11,900 + 3,100 - 23,900 = -8,750 ohms

The conditional equation now becomes:

(R_g + 15,100) (R_L - 8,750) + 8,900 (15,000) > 0.

This stabilized conditional stability line is also plotted on Fig. 4-14.

The maximum available gain, defined by equation 3-55

can be applied to junction transistors, since the stability factor is not greater than one. In the grounded collector connection, since δ is always very near unity, this equation can be simplified as:

Eq. (4-18)*

Notice that this result is nothing more than the product of the maximum voltage gain - and the maximum current gain - .The

maximum available gain in terms of the transistor internal parameters is:

Eq. (4-19)

Eq, (4-20)

For the typicaljunction transistor