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**Types of BJT Biasing Circuits**

By G.Kavitha ECE Dept Paavai Engineering College

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**Biasing Circuits of the BJT**

Normally, three types of circuits are used to establish dc biasing in a BJT, these are; (a) Fixed bias circuit (b) Collector-to-Base Bias Circuit (c) Voltage-Divider with Self-Bias Circuit (or) Self-Bias (or) Emitter Bias (or) Emitter-Stabilized Bias Circuit While designing the all four types of biasing circuits of BJT it is aimed to obtain Q-point parameters (IBQ, ICQ, VCEQ)

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Fixed Bias

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**The Base-Emitter Loop From Kirchhoff’s voltage law:**

+VCC – IBRB – VBE = 0 Solving for base current:

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**Collector-Emitter Loop**

Collector current: From Kirchhoff’s voltage law:

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Saturation When the transistor is operating in saturation, current through the transistor is at its maximum possible value.

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**The end points of the load line are: ICsat**

Load Line Analysis The end points of the load line are: ICsat IC = VCC / RC VCE = 0 V VCEcutoff VCE = VCC IC = 0 mA The Q-point is the operating point: where the value of RB sets the value of IB that sets the values of VCE and IC

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Collector to Base Bias

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**Base-Emitter Loop From Kirchhoff’s voltage law: Where IB << IC:**

Knowing IC = IB and IE IC, the loop equation becomes: Solving for IB:

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**Collector-Emitter Loop**

From Kirchhoff’s voltage law: Since IC IC and IC = IB: Solving for VCE:

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**Voltage Divider Bias (or) Self Bias**

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**Approximate Analysis Where IB << I1 and I1 I2 :**

Where bRE > 10R2: From Kirchhoff’s voltage law:

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**Voltage Divider Bias Analysis**

Transistor Saturation Level Load Line Analysis Cutoff: Saturation:

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**Emitter-Stabilized Bias Circuit**

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**Base-Emitter Loop From Kirchhoff’s voltage law: Since IE = (b + 1)IB:**

Solving for IB:

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**Collector-Emitter Loop**

From Kirchhoff’s voltage law: Since IE IC: Also:

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**Improved Biased Stability**

Stability refers to a circuit condition in which the currents and voltages will remain fairly constant over a wide range of temperatures and transistor Beta () values. Adding RE to the emitter improves the stability of a transistor.

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**Saturation Level The endpoints can be determined from the load line.**

VCEcutoff: ICsat:

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**Emitter-Stabilized Bias Circuit**

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**Base-Emitter Loop From Kirchhoff’s voltage law: Where IB << IC:**

Knowing IC = IB and IE IC, the loop equation becomes: Solving for IB:

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**Collector-Emitter Loop**

From Kirchhoff’s voltage law: Since IC IC and IC = IB: Solving for VCE:

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**Base-Emitter Bias Analysis**

Transistor Saturation Level Load Line Analysis Cutoff: Saturation:

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THANK YOU

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