Current Gain of the Grounded Collector Connection

Author: Leonard Krugman

The current gain as defined in equation 3-8 is:

In terms of the internal transistor parameters in the grounded collector connection, the current gain becomes:

Eq. (4-14)

The value of r₂₂ is always negative in the case of the point-contact transistor. Therefore, the load resistor R_L must be larger than the absolute value of r₂₂ for stable operation, and the equation for maximum current gaincan only be applied to the junction transistor.

Numerical values for the typical junction transistor when R_L = 100,000 ohms are

and the maximum current gain

For the point-contact transistor when R_L = 15,000 ohms,

It would appear that as the load approaches the absolute value of r₂₂, extremely high current gains are attainable. For example, for the point-contact transistor when R_L = 11,950 ohms,

In operating circuits, however, the grounded collector current gain is limited to the same order of magnitude as in the grounded emitter connection. This limitation is caused by the rapid increase in input resistance with an increase in current gain.