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# BJT Emitter Stabilized Bias - PowerPoint PPT Presentation

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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## PowerPoint Slideshow about ' BJT Emitter Stabilized Bias' - arden-daniel

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### BJT Emitter Stabilized Bias

ELEC 121

• 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

• Draw Equivalent Input circuit

• DrawEquivalent Output circuit

• Write necessary KVL and KCL Equations

• Determine the Quiescent Operating Point

• Perform a Computational Analysis

ELEC 121

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

ELEC 121

ELEC 121

ELEC 121

ELEC 121

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

ELEC 121

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

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

The load line end points can be calculated:

At cutoff:

At saturation:

ELEC 121

Where .1VCC VE  .2VCC

And .4VCC VC  .6VCC

ELEC 121

ELEC 121

Input Output

ELEC 121