Emitter Follower Calculator

An emitter follower is a common transistor circuit configuration used in electronics to provide impedance matching and voltage buffering. This calculator helps you determine key parameters of an emitter follower circuit based on your component values.

What is an Emitter Follower?

An emitter follower is a type of common emitter amplifier circuit where the emitter of the transistor is connected to the input signal. This configuration provides several important characteristics:

High input impedance (resistance to current flow)
Low output impedance
Voltage gain of approximately 1
Phase inversion (180° phase shift)

The emitter follower is commonly used as a buffer stage between high-impedance sources and low-impedance loads. It's particularly useful in audio amplifiers and signal conditioning circuits.

Emitter Follower Formula

The key parameters of an emitter follower can be calculated using the following formulas:

Voltage Gain (A_v) = 1 / (1 + β) where β is the current gain of the transistor

Input Resistance (R_in) = (β + 1) * R_L where R_L is the load resistance

Output Resistance (R_out) = R_E / (β + 1) where R_E is the emitter resistance

These formulas are implemented in the calculator to provide accurate results based on your input values.

How to Use the Calculator

Enter the current gain (β) of your transistor
Input the load resistance (R_L) in ohms
Specify the emitter resistance (R_E) in ohms
Click "Calculate" to see the results
Review the calculated parameters and chart visualization

The calculator will display the voltage gain, input resistance, and output resistance of your emitter follower circuit.

Example Calculation

Let's calculate the parameters for an emitter follower with:

Current gain (β) = 100
Load resistance (R_L) = 1000Ω
Emitter resistance (R_E) = 100Ω

Using the formulas:

Voltage Gain = 1 / (1 + 100) ≈ 0.0099 Input Resistance = (100 + 1) * 1000 = 101,000Ω Output Resistance = 100 / (100 + 1) ≈ 0.99Ω

These values show the emitter follower's characteristics: low voltage gain, high input impedance, and very low output impedance.

FAQ

What is the main advantage of an emitter follower?

The main advantage is its high input impedance, which makes it ideal for buffering signals from high-impedance sources without loading them significantly.

Why does an emitter follower have a voltage gain of approximately 1?

The voltage gain is close to 1 because the emitter voltage follows the base voltage with minimal attenuation, creating a buffer effect.

What happens if the current gain (β) of the transistor changes?

Changes in β will affect the voltage gain and output resistance. Higher β values will increase the voltage gain and decrease the output resistance.

Can emitter followers be used in audio circuits?

Yes, emitter followers are commonly used in audio circuits as buffer stages between different impedance levels to prevent signal distortion.