Amp Calculator Cathode Follower

This amp calculator helps you determine the performance characteristics of a cathode follower circuit, including voltage gain, current gain, and output impedance. The calculator provides quick results based on your input parameters and explains the underlying principles.

Introduction

A cathode follower is a type of amplifier circuit that uses a triode vacuum tube or a field-effect transistor (FET) to provide voltage buffering between stages. It's called a "follower" because the output voltage follows the input voltage, but with some gain and impedance transformation.

Cathode followers are commonly used in audio amplifiers, radio receivers, and other electronic circuits where voltage buffering is needed. They offer several advantages including high input impedance, low output impedance, and excellent linearity.

Cathode Follower Basics

The basic cathode follower circuit consists of a triode vacuum tube with the grid connected to the input signal, the cathode connected to the output through a resistor, and the plate connected to a positive voltage supply.

Key Characteristics

Voltage gain is typically between 0.7 and 0.9
Current gain is very high (often 100 or more)
Output impedance is very low (often less than 100 ohms)
Input impedance is very high (often thousands of ohms)
Excellent linearity and low distortion

These characteristics make cathode followers ideal for buffering signals between stages of amplification, where the goal is to maintain the signal's integrity while providing some gain.

How to Use the Calculator

To use the amp calculator for cathode followers, follow these steps:

Enter the plate voltage (V_P) in volts
Enter the cathode resistor value (R_K) in ohms
Enter the load resistor value (R_L) in ohms
Click the "Calculate" button

The calculator will display the voltage gain, current gain, and output impedance based on your input parameters.

Formula Explanation

The calculator uses the following formulas to determine the performance characteristics of the cathode follower:

Voltage Gain (A_V) = V_out/V_in = R_L/(R_K + R_L) Current Gain (A_I) = I_out/I_in = (V_P - V_out)/R_K / (V_in/R_in) Output Impedance (R_out) = R_K || R_L

Where:

V_P = Plate voltage
R_K = Cathode resistor value
R_L = Load resistor value
V_in = Input voltage
V_out = Output voltage
I_in = Input current
I_out = Output current
R_in = Input resistance

Example Calculation

Let's consider a cathode follower with the following parameters:

Plate voltage (V_P) = 250V
Cathode resistor (R_K) = 10kΩ
Load resistor (R_L) = 1kΩ

Using the formulas above, we can calculate:

Voltage Gain (A_V) = 1kΩ/(10kΩ + 1kΩ) = 0.0909 or -9.09dB Current Gain (A_I) = (250V - V_out)/10kΩ / (V_in/R_in) Output Impedance (R_out) = 10kΩ || 1kΩ = 909Ω

This example shows that the cathode follower provides significant voltage buffering while maintaining good current gain and low output impedance.

Frequently Asked Questions

What is the main advantage of a cathode follower?

The main advantage of a cathode follower is its high input impedance and low output impedance, which makes it ideal for buffering signals between stages of amplification.

What is the typical voltage gain of a cathode follower?

The typical voltage gain of a cathode follower is between 0.7 and 0.9, which means it provides some gain while maintaining good signal integrity.

How does the cathode resistor affect the performance of a cathode follower?

The cathode resistor (R_K) affects the voltage gain and current gain of the cathode follower. A larger R_K will result in higher voltage gain but lower current gain.

What is the difference between a cathode follower and an emitter follower?

A cathode follower uses a triode vacuum tube or FET, while an emitter follower uses a bipolar junction transistor (BJT). Both provide similar buffering characteristics but with different component types.