Voltage Follower Circuit Overview

Voltage Follower Circuit

  • Definition: A voltage follower circuit is a special case of a non-inverting amplifier.
  • Basic Formula: In a non-inverting amplifier, the output voltage (V_out) is calculated as:
  • Vout = Vsubs * R1 / (R2 + 1)
Transition to Voltage Follower
  • To transform a non-inverting amplifier into a voltage follower:
  • Let R1 become 0 (short circuit).
  • Let R2 approach infinity (remove the feedback branch).
  • Resulting Output Equation: Vout = 1 * Vsubs
  • Meaning: The output voltage is equal to the input voltage.
Purpose of Voltage Follower
  • Output Follows Input: The output simply follows the input – hence the name voltage follower.
  • Buffer Amplifier: Another common name for the voltage follower, indicating its role in buffering the source.
  • Current Handling: In an ideal voltage follower, the current at the input terminal is minimal, ideally zero, which means:
  • The source voltage can be maintained without significant current draw from the source.
Importance in Electrical Circuits
  • High Thevenin Resistance Sources: If using a source with high Thevenin equivalent resistance, even a small current drawn can result in a significant voltage drop.
  • Voltage Maintenance: The voltage follower preserves the desired voltage even when the source has high resistance.
Functionality and Utility
  • Output Current: The output current is supplied by external power supplies (V+ and V-), not the voltage source.
  • Typical Output Currents: Realistic operational amplifiers can provide output currents from 10 to 50 milliamps, sufficient for most applications.
  • Current Gain: Acts as a current gain amplifier with no input current and a finite output current.
Applications of Voltage Followers
  • Transducers: Often used with transducers, which are devices that measure physical properties (pressure, temperature, humidity, etc.) and convert them into voltages, currents, or resistance changes.
  • Transducers typically have high output resistances and low source voltages, thus needing a buffer to drive control circuits.
  • Control Systems: Useful in systems requiring accurate measurements of physical properties and subsequent control of voltage or current based on those measurements.
  • Instrumentation Amplifiers: In more advanced studies, instrumentation amplifiers, specifically designed for interfacing with high-impedance sources, will be discussed.
Key Takeaways
  • A voltage follower preserves the input voltage, minimizes loading on the source, and allows for higher output currents to drive subsequent circuits.