Circuit Construction - 6.4.2 | EXPERIMENT NO. 5: POWER AMPLIFIERS AND FEEDBACK ANALYSIS | Analog Circuit Lab
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6.4.2 - Circuit Construction

Practice

Definitions & Key Concepts

Learn essential terms and foundational ideas that form the basis of the topic.

Key Concepts

  • Op-Amp Power: Always connect dual power supplies correctly to the Op-Amp before any signal connections.

  • Feedback Loop: The path from output through R1 to the inverting input, and R2 from inverting input to ground, forms the feedback loop.

  • Voltage Divider: The R1-R2 network acts as a voltage divider, determining the feedback factor.

  • Input Application: Input signal always goes to the non-inverting terminal for this configuration.

  • Pre-Power Check: Essential to avoid damaging the sensitive Op-Amp.

  • Examples

  • LM741 Pinout: When placing an LM741, you'd note that pin 7 is +Vcc, pin 4 is -Vcc, pin 2 is Inverting Input, pin 3 is Non-inverting Input, and pin 6 is Output. Your wiring must match these physical pins.

  • Resistor Placement: If you choose R1 = 9 kΩ and R2 = 1 kΩ for a gain of 10, you would connect the 9 kΩ resistor between pin 6 and pin 2, and the 1 kΩ resistor between pin 2 and the ground rail.

  • Input Connection: Your function generator's output lead would connect to pin 3 of the LM741.

  • Flashcards

  • Term: Op-Amp Power Supply

  • Definition: Requires precise connection of +Vcc, -Vcc, and Ground to the correct pins for the Op-Amp to function.

  • Term: Non-inverting Input (+)

  • Definition: The Op-Amp terminal where the primary input signal is applied in a non-inverting amplifier configuration.

  • Term: Feedback Resistors (R1, R2)

  • Definition: The two resistors that form a voltage divider to sample the output and feed a fraction back to the inverting input.

  • Term: Decoupling Capacitors (Op-Amp)

  • Definition: Small capacitors placed near Op-Amp power pins to reduce noise and improve stability.

  • Term: Pre-Power Verification

  • Definition: The critical step of visually and/or electrically checking all connections before applying power to prevent damage.

  • Memory Aids

  • "O.P. P.O.W.E.R.": Op-Amp Pins, Power Orientation With Exact Resistors (R1 & R2).

  • "Feedback Loop = Circle": The signal goes out of the Op-Amp and circles back to the input through the resistors.

  • "Non-inverting = No Inversion": The output waveform will look just like the input, just amplified.

Examples & Real-Life Applications

See how the concepts apply in real-world scenarios to understand their practical implications.

Examples

  • LM741 Pinout: When placing an LM741, you'd note that pin 7 is +Vcc, pin 4 is -Vcc, pin 2 is Inverting Input, pin 3 is Non-inverting Input, and pin 6 is Output. Your wiring must match these physical pins.

  • Resistor Placement: If you choose R1 = 9 kΩ and R2 = 1 kΩ for a gain of 10, you would connect the 9 kΩ resistor between pin 6 and pin 2, and the 1 kΩ resistor between pin 2 and the ground rail.

  • Input Connection: Your function generator's output lead would connect to pin 3 of the LM741.

  • Flashcards

  • Term: Op-Amp Power Supply

  • Definition: Requires precise connection of +Vcc, -Vcc, and Ground to the correct pins for the Op-Amp to function.

  • Term: Non-inverting Input (+)

  • Definition: The Op-Amp terminal where the primary input signal is applied in a non-inverting amplifier configuration.

  • Term: Feedback Resistors (R1, R2)

  • Definition: The two resistors that form a voltage divider to sample the output and feed a fraction back to the inverting input.

  • Term: Decoupling Capacitors (Op-Amp)

  • Definition: Small capacitors placed near Op-Amp power pins to reduce noise and improve stability.

  • Term: Pre-Power Verification

  • Definition: The critical step of visually and/or electrically checking all connections before applying power to prevent damage.

  • Memory Aids

  • "O.P. P.O.W.E.R.": Op-Amp Pins, Power Orientation With Exact Resistors (R1 & R2).

  • "Feedback Loop = Circle": The signal goes out of the Op-Amp and circles back to the input through the resistors.

  • "Non-inverting = No Inversion": The output waveform will look just like the input, just amplified.

Memory Aids

Use mnemonics, acronyms, or visual cues to help remember key information more easily.

🧠 Other Memory Gems

  • Op-Amp Pins, Power Orientation With Exact Resistors (R1 & R2).
    *     "Feedback Loop = Circle"

🧠 Other Memory Gems

  • The output waveform will look just like the input, just amplified.

Flash Cards

Review key concepts with flashcards.

Glossary of Terms

Review the Definitions for terms.

  • Term: Decoupling Capacitors

    Definition:

    Small capacitors placed close to IC power pins to filter out high-frequency noise from the power supply lines.

  • Term: PrePower Check

    Definition:

    Essential to avoid damaging the sensitive Op-Amp.

  • Term: Input Connection

    Definition:

    Your function generator's output lead would connect to pin 3 of the LM741.

  • Term: Definition

    Definition:

    The critical step of visually and/or electrically checking all connections before applying power to prevent damage.

  • Term: "Noninverting = No Inversion"

    Definition:

    The output waveform will look just like the input, just amplified.

Detailed Explanation

Constructing a voltage-series negative feedback amplifier, particularly using an Operational Amplifier (Op-Amp) in a non-inverting configuration, is fundamental to understanding feedback principles. The Op-Amp inherently has a very high open-loop gain, and negative feedback is used to stabilize this gain and improve other performance parameters.

The construction focuses on building the non-inverting amplifier circuit as depicted in Figure 5.3.

  1. Op-Amp Placement and Power Supply Connections (Crucial First Step):
    • Place the Op-Amp: Carefully insert the Op-Amp IC (e.g., LM741, TL082) onto the breadboard. Ensure the notch or dot indicating Pin 1 is correctly oriented. Incorrect orientation can lead to immediate damage upon power-up.
    • Power Supply: Connect the Op-Amp's power supply pins:
      • +Vcc (positive supply): Connect the appropriate pin (e.g., Pin 7 for LM741) to the positive power rail of your breadboard.
      • -Vcc (negative supply): Connect the appropriate pin (e.g., Pin 4 for LM741) to the negative power rail of your breadboard.
      • Ground: Ensure the ground reference of your power supply is also connected to the breadboard's ground rail.
    • Decoupling Capacitors (Highly Recommended, though not explicitly in schematic): For stable Op-Amp operation, it's good practice to place small decoupling capacitors (e.g., 0.1 µF ceramic) as close as possible to the Op-Amp's power supply pins, from each power pin to ground. These help filter out high-frequency noise on the power lines.
  2. Input Signal Connection:
    • Non-inverting Input: Connect the input signal (Vin) from your AC Function Generator to the Op-Amp's non-inverting input pin (e.g., Pin 3 for LM741). A small input coupling capacitor can be used if the signal source has a DC offset.
  3. Feedback Network Construction (Voltage-Series Negative Feedback):
    • This is the core of the negative feedback implementation for the non-inverting amplifier.
    • Resistor R1 (Feedback Resistor 1): Connect one end of R1 from the Op-Amp's output pin (e.g., Pin 6 for LM741) to its inverting input pin (e.g., Pin 2 for LM741). This resistor feeds a portion of the output voltage back to the inverting input.
    • Resistor R2 (Feedback Resistor 2): Connect one end of R2 from the Op-Amp's inverting input pin (the same point as R1) to ground. This resistor completes the voltage divider that samples the output.
    • Feedback Factor (Beta, $\beta$): This feedback network forms a voltage divider that sets the feedback factor. For this configuration, the fraction of the output voltage fed back to the inverting input is $\beta = R\_2 / (R\_1 + R\_2)$.
  4. Output Connection:
    • Output Terminal: The amplifier's output (Vout) is directly taken from the Op-Amp's output pin (e.g., Pin 6 for LM741). Connect this to your oscilloscope or load.
  5. Verification and Double-Checking (CRITICAL):
    • Visual Inspection: Before connecting the power supply to the breadboard, meticulously check all connections:
      • Op-Amp Orientation: Is the Op-Amp inserted correctly (Pin 1)?
      • Power Supply Polarity: Are +Vcc and -Vcc connected to the correct pins and breadboard rails? Is ground connected?
      • Input Connection: Is Vin going to the non-inverting input?
      • Feedback Connections: Are R1 and R2 connected precisely as described, creating the voltage divider from output to inverting input to ground?
      • Component Values: Are R1 and R2 the correct calculated values?
      • No Shorts: Ensure no bare wires or component leads are accidentally touching, especially between power rails or signal lines.
    • Continuity Check (Recommended): Use a DMM to verify there are no shorts between the Op-Amp's power pins or between power pins and ground.

Why this construction is important:

  • Fundamental Feedback: This circuit is a classic example of voltage-series negative feedback, demonstrating how feedback stabilizes gain and improves performance.
  • Practical Op-Amp Use: It's one of the most common and versatile Op-Amp configurations.
  • Parameter Measurement: The clear, predictable behavior of this circuit allows for accurate measurement of gain, impedance, and bandwidth changes due to feedback.