Merits and demerits of fixed bias, Electrical Engineering


1.      It is very simple to shift the operating point anywhere in the active region by just changing the base resistor (RB).

2.      A very small number of components are needed.


  • The collector current does not stay constant with difference in temperature or power supply voltage. Hence the operating point is unstable.
  • Variations in Vbewill change IBand so cause REto change. In turn this will alter the gain of the stage.
  • When the transistor is changed with other one, considerable change in the value of β can be supposed. Because of this change the operating point will shift.
  • For small-signal transistors (for example not power transistors) with comparatively high values of β (that is, between 100 and 200), this configuration will be prone to thermal runaway. Particularly, the stability factor which is a measure of the change in collector current with changes in reverse saturation current is almost β+1. To make sure absolute stability of the amplifier, a stability factor of less than 25 is chosen and so small-signal transistors comprises large stability factors.


Posted Date: 1/10/2013 7:06:30 AM | Location : United States

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