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Improved Transistor Amplifier

<^< Worksheet: Simple Transistor Amplifier | Course Index | Worksheet: Improved Transistor Amplifier >^>(:nl:)

In order to stabilize the operating conditions of the simple transistor amplifier stage and compensate for variations in transistor parameters and temperature, base bias current (I'_B_') for the transistor can be derived from the voltage at the collector (V'_CE_') rather than from the supply (V'_CC_'). The value of V'_CE_' is dependent on the collector current which, in turn, depends upon the base current. A negative feedback path thus exists which provides a degree of self-regulation. The feedback action works like this:

If I'_C_' increases, V'_CE_' will fall and I'_B_' will be reduced. The reduction in I'_B_' will, in turn, produce a corresponding reduction in I'_C_' to offset the original change. Conversely, if I'_C_' falls, V'_CE_' will rise and I'_B_' will increase. This, in turn, will produce a corresponding increase in I'_C_' to oppose the original change.

Typical values are as follows;

* TR'_1_' = BC108, * V'_CC_' = 6V, * R'_1_' = 470k&#937;, * R'_2_' = 1k&#937;, and * C'_1_' = C'_2_' = 10&#956;F.

Note that, once again, the output signal will be inverted (i.e. 180° out of phase with the input). (:nl:)(:table style="clear:both":)