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Premium experiment • feedback vs rail limits

COMPUTER SCIENCE & TECHNOLOGY • ELECTRONICS

Operational Amplifier (Op-Amp) Circuits

Compare inverting, non-inverting and comparator configurations while watching resistor gain and supply-rail saturation.

● IDEAL OP-AMP + RAILSAnalog amplifier
Closed-loop gain
Ideal output
Actual output
Region

Reasoning inspector

live model state
Mode—
Input Vin—
Closed-loop gain—
Ideal output—
Actual output—
Supply rails—
Output headroom—
Operating state—
Rf / R1—

Feedback sets useful gain

Ideal op-amp equations predict the requested output from the feedback network. The supply rails then reveal when that ideal output is no longer physically available.

LEARN WITH THE SIMULATION

Understand Operational Amplifier (Op-Amp) Circuits by experimenting.

START HERE

Operational amplifiers use enormous open-loop differential gain together with feedback to create predictable closed-loop behavior. This laboratory focuses on ideal inverting and non-inverting feedback plus comparator operation, while making one practical constraint impossible to ignore: the requested ideal output may lie beyond the supply rails. The premium inspector separates gain, ideal output, actual clipped output, resistor ratio and remaining rail headroom.

BUILD THE IDEA

What you should understand first

  • Calculate ideal closed-loop gain from resistor ratios for inverting and non-inverting configurations.
  • Distinguish ideal requested output from the rail-limited output the powered model can deliver.
  • Interpret negative feedback as the mechanism that makes resistor-defined gain useful.
  • Explain why comparator mode intentionally drives toward a rail rather than operating as a linear amplifier.

TRY IT YOURSELF

When does changing resistor ratio stop changing the actual output?

  1. Use inverting mode with a modest input and increase Rf/Rin while watching ideal and actual output.
  2. Identify the point where the ideal magnitude reaches the supply rail.
  3. Continue increasing Rf and observe ideal output continue to grow while actual output remains clipped.
  4. Raise the rail voltage and verify that linear behavior is restored if the ideal value fits inside the new limits.
Read the visual:

Feedback equations determine the ideal closed-loop output only while that output is physically available. Once the requested value exceeds the modeled rails, the output saturates and no longer follows the linear gain equation.

WHY IT WORKS 01

Feedback turns huge open-loop gain into a resistor-defined closed-loop gain

An ideal op-amp responds to a tiny difference between its inputs with a huge output change. With negative feedback, the circuit drives itself toward a state where the input difference is very small, allowing resistor relationships to determine a stable closed-loop gain. For an inverting amplifier this gives −Rf/Rin; for a non-inverting amplifier it gives 1 + Rf/Rg.

WHY IT WORKS 02

Supply rails create a hard distinction between requested and available output

The algebra can request any ideal output, but a powered amplifier cannot produce a voltage beyond its supply capability. The simulator clips output to ±Vrail, so the inspector shows both the ideal value and the realizable value. Headroom measures how far the current actual output remains from the modeled rail limit.

WHY IT WORKS 03

A comparator uses the same differential idea for a different purpose

Without linear negative feedback, a comparator asks only which input is larger. The output then moves toward the positive or negative rail according to that sign. The resistor-defined linear gains used in inverting and non-inverting amplifiers are therefore not the right mental model for comparator operation.

DO NOT MIX THESE UP

Common misconception

The closed-loop gain formula does not imply unlimited voltage. An op-amp also does not force its two inputs to be equal in every situation; the virtual-short approximation depends on negative feedback and unsaturated linear operation. Comparator mode deliberately leaves that linear regime and drives the output toward one rail or the other.

PRACTICE CHALLENGE

Can you reach a target output without saturation, then deliberately force the same setup into saturation by changing only the rails?

  • Choose a target output voltage.
  • Use input voltage and resistor ratio to approach the target in a linear amplifier mode.
  • Verify that ideal and actual outputs agree and inspect remaining headroom.
  • Lower the rail magnitude until clipping appears, then explain why changing gain no longer produces the expected actual output.
Reveal the reasoning

A linear target is achievable when the closed-loop ideal output lies inside the available rails. In that regime actual output follows the feedback gain equation. If the same ideal output lies beyond ±Vrail, the model clips it at the rail and the circuit is saturated, so the linear gain relation no longer predicts the actual output.

MODEL BOUNDARIES

What this simulation assumes

Every simulation simplifies reality or a mathematical system. These are the assumptions and limits to keep in mind while interpreting the results.

Model assumptions

  • The op-amp is ideal inside the output-rail limits, with infinite open-loop gain and no input current.
  • Inverting and non-inverting gains are set only by the displayed resistor ratios.
  • Comparator mode switches directly between symmetric positive and negative rails.

Model limitations

  • Bandwidth, slew rate, offset voltage, common-mode limits, output current and rail headroom are omitted.
  • Real comparator and op-amp transitions are not instantaneous or perfectly ideal.

CONNECT IT

Where this matters

  • Signal conditioning
  • Active filters and sensor interfaces
  • Comparators and analog control
  • Gain stages in instrumentation

WORDS THAT MATTER

Key vocabulary

Closed-loop gain
Amplifier gain established by external feedback rather than raw open-loop gain.
Negative feedback
Returning output information in a way that reduces input error and stabilizes linear operation.
Saturation
Condition where requested output exceeds available rail range and the actual output clips.
Headroom
Remaining voltage margin between the current output magnitude and the supply rail.
Comparator
Circuit mode that selects a rail according to the sign of an input difference rather than linear gain.