Output Resistance of Emitter Follower Calculator

Formula Used:

\[ R_{fi} = \left( \frac{1}{R_L} + \frac{1}{V_{sig}} + \frac{1}{R_e} \right) + \frac{ \left( \frac{1}{Z_{base}} + \frac{1}{R_{sig}} \right) }{ \beta + 1 } \]

Load Resistance (R_L):

Small Signal Voltage (V_sig):

Emitter Resistance (R_e):

Base Impedance (Z_base):

Signal Resistance (R_sig):

Collector Base Current Gain (β):

Finite Resistance (R_fi):

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1. What is Output Resistance of Emitter Follower?

The output resistance of an emitter follower is a measure of how much the output voltage changes with changes in output current. It represents the internal resistance looking back into the output terminals of the circuit when all independent sources are turned off.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ R_{fi} = \left( \frac{1}{R_L} + \frac{1}{V_{sig}} + \frac{1}{R_e} \right) + \frac{ \left( \frac{1}{Z_{base}} + \frac{1}{R_{sig}} \right) }{ \beta + 1 } \]

Where:

\( R_L \) — Load Resistance (Ω)
\( V_{sig} \) — Small Signal Voltage (V)
\( R_e \) — Emitter Resistance (Ω)
\( Z_{base} \) — Base Impedance (Ω)
\( R_{sig} \) — Signal Resistance (Ω)
\( \beta \) — Collector Base Current Gain

Explanation: The formula calculates the finite resistance by combining parallel resistances and accounting for the current gain factor in the transistor circuit.

3. Importance of Finite Resistance Calculation

Details: Calculating the output resistance is crucial for understanding the loading effects, voltage regulation capability, and overall performance of emitter follower circuits in amplifier design.

4. Using the Calculator

Tips: Enter all resistance values in ohms (Ω), voltage in volts (V), and current gain as a dimensionless quantity. All values must be positive and non-zero.

5. Frequently Asked Questions (FAQ)

Q1: What is an emitter follower circuit?
A: An emitter follower is a type of bipolar junction transistor (BJT) configuration that provides high input impedance, low output impedance, and voltage gain approximately equal to 1.

Q2: Why is output resistance important in emitter followers?
A: Low output resistance allows the emitter follower to drive heavy loads without significant voltage drop, making it useful as a buffer stage in amplifier circuits.

Q3: How does β affect the output resistance?
A: Higher β values typically result in lower output resistance, as the transistor provides more current gain and better impedance transformation.

Q4: What are typical values for emitter follower output resistance?
A: Output resistance typically ranges from a few ohms to several hundred ohms, depending on the circuit parameters and transistor characteristics.

Q5: Can this calculator be used for other transistor configurations?
A: No, this specific formula is designed for emitter follower configuration. Other configurations have different formulas for output resistance calculation.