Stabilization Of Operating Point | Electrical Engineering

transweb 3,733 views 12 slides Jun 20, 2017
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Biasing of BJT amplifiers plays an important role in operation of these amplifiers. Broadly biasing means application of DC voltage for amplification of AC signal. For individual devices biasing circuit mainly includes resistance. Copy the link given below and paste it in new browser window to get m...


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Stabilization of operating point

BJT load line It is plotted from DC equivalent circuit In this collector current at is determined at saturation and collector emitter voltage at cut-off.

Operating point or Q-point It is the point at which transistor is biased It is determined on DC load line

Operating point stability It depends on various factor Variation of current gain Variation of temperature Variation of reverse saturation current Variation of base emitter voltage Improper regulation of supply voltage

Effect of variation of current gain For higher current gain operating point shifts towards saturation.

Effect of variation of temperature For higher temperature, keeping base current constant operating point shifts towards saturation.

Types of bias circuit Fixed bias Collector base bias Fixed bias with emitter resistance Voltage divider bias

Fixed bias Base current is given by Collector current is DC equivalent circuit

Collector base bias This arrangement is more sensitive to temperature variation. Base current is DC equivalent circuit

Fixed bias with emitter resistance It has additional resistive element on emitter terminal. It improves stability. Base current is DC equivalent circuit

Voltage divider bias Potential divider circuit is implemented. Voltage across resistance R2 is taken as base voltage. Base voltage is DC equivalent circuit is

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