This document discusses the stabilization of operating point in BJTs. It defines the load line and operating point, and explains that the operating point depends on factors like current gain, temperature, and supply voltage variations. An increase in current gain or temperature will shift the operating point towards saturation. It also describes different bias circuit types - fixed bias, collector base bias, fixed bias with emitter resistance, and voltage divider bias - and provides their basic equations.

1. Stabilization of operating point

2. 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.

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

4. 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

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

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

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

8. Fixed bias
 Base current is given by
 Collector current is
 DC equivalent circuit

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

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

11. 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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