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BJT Emitter Stabilized Bias. ELEC 121. Improved Bias Stability. The addition of R E to the Emitter circuit improves the stability of a transistor output

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Improved Bias Stability

  • The addition of RE to the Emitter circuit improves the stability of a transistor output

    • Stability refers to a bias circuit in which the currents and voltages will remain fairly constant over a wide range of temperatures and transistor forward current gain ()

    • The temperature (TA or ambient temperature) surrounding the transistor circuit is not always constant

    • Therefore, the transistor  is not a constant value

ELEC 121


Bjt emitter bias
BJT Emitter Bias

  • Draw Equivalent Input circuit

  • DrawEquivalent Output circuit

  • Write necessary KVL and KCL Equations

  • Determine the Quiescent Operating Point

    • Graphical Solution using Loadlines

    • Perform a Computational Analysis

ELEC 121


Emitter-Stabilized Bias Circuit

Adding an emitter resistor to the circuit between the emitter lead and ground stabilizes the bias circuit over Fixed Bias

ELEC 121





Base-Emitter Loop

Applying Kirchoffs voltage law: - VCC + IB RB + VBE +IE RE = 0

Since: IE = ( + 1) IB

We can write: - VCC + IB RB + VBE + ( + 1) IBRE = 0

Grouping terms and solving for IB:

Or we could solve for IE with:

ELEC 121



Collector-Emitter Loop

Applying Kirchoff’s voltage law: - VCC + IC RC + VCE + IE RE = 0

Assuming that IE IC and solving for VCE: VCE=VCC – IC (RC + RE)

If we can not use IE IC the IC = IE and:VCE=VCC – IC (RC + RE)

Solve for VE: VE = IE RE

Solve for VC: VC = VCC - IC RC

or

VC = VCE + IE RE

Solve for VB: VB = VCC - IB RB

or

VB = VBE + IE RE

ELEC 121


Transistor Saturation

At saturation, VCE is at a minimum

We will find the value VCEsat = 0.2V

For load line analysis, we use VCE = 0

To solve for ICSAT, use the output KVL equation:

ELEC 121


Load Line Analysis

The load line end points can be calculated:

At cutoff:

At saturation:

ELEC 121



Design of an emitter bias ce amplifier
Design of an Emitter Bias CE Amplifier

Where .1VCC VE  .2VCC

And .4VCC VC  .6VCC

ELEC 121



Emitter bias with dual supply1
Emitter Bias with Dual Supply

Input Output

ELEC 121


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