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Current Gain

Author: Leonard Krugman

The current gain, transistor_basics_03-48.gif, when the circuit is working into the load RL, becomes the ratio of equation 3-4 to equation 3-3

transistor_basics_03-49.gif

 Eq. (3-7)*

and in terms of the openrcircuit parameters, the current gain is the ratio of equation 3-6 to equation 3-5

transistor_basics_03-50.gif

 Eq. (3-8)*

The current gain as derived in equations 3-7 and 3-8 indicates the effect of the load resistance RL on α, but does not take into account the effect of mismatch between the signal generator resistance and the input resistance of the transistor. It is evident that the maximum current gain is obtained when the load resistance RL = O. Thus, the maximum

transistor_basics_03-51.gif

 Eq. (3-8A)*

Since rb is very small in comparison with either rm or rc, it may be neglected in equation 3-8A, and a rather accurate estimate of the maximum current gain is

transistor_basics_03-52.gif

 Eq. (3-8B)*

A frequently used form for the current gain, which incorporates the maximum current gain ao, is

transistor_basics_03-53.gif

 Eq. (3-8C)*

Home The Grounded Base Transistor The Grounded Base Connection Current Gain

Last Update: 2010-11-17