Question about bistable multivibrator op amps

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SUMMARY

The discussion focuses on the operation of bistable multivibrators using operational amplifiers (op amps). Key points include the behavior of output voltage, which caps at 0.7V due to hysteresis, and the feedback mechanism that differentiates it from a standard non-inverting amplifier. The importance of the 10k resistor is highlighted, as it limits the output current to prevent saturation. Understanding these concepts is crucial for analyzing circuit behavior in bistable configurations.

PREREQUISITES
  • Understanding of operational amplifier configurations
  • Knowledge of hysteresis in electronic circuits
  • Familiarity with Kirchhoff's Voltage Law (KVL) and Kirchhoff's Current Law (KCL)
  • Basic circuit analysis techniques
NEXT STEPS
  • Study the principles of hysteresis in bistable multivibrators
  • Learn about the role of feedback in op amp circuits
  • Explore the differences between non-inverting and inverting amplifier configurations
  • Investigate the impact of resistor values on op amp output behavior
USEFUL FOR

Electronics students, circuit designers, and engineers interested in understanding bistable multivibrators and operational amplifier applications.

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Homework Statement


Here is the problem:
XMrhesR.png


So this is a bistable multivibrator.

Homework Equations


KVL and KCL laws

The Attempt at a Solution


I don't entirely understand bistable multivibrators. I get what the solution is, the input voltage caps at 0.1V and the output caps at 0.7V and hysteresis occurs. Apparently, the output voltage will feed back into the + terminal of the op amp and this loops repeats itself until saturation... Why doesn't this happen with a regular non-inverting amplifier. The configuration is almost the same except the terminals are flipped... What does this mean?

However, when I do some circuit analysis I notice that if the input is greater than 0.1V weird things happen. For example take a look at what I did here:

ahMgoHA.jpg


So when you have 5V as the input, what happens to the current flow, does some of it just magically get capped?

Another question I have is what is that 10k resistor right after the op amp used for?
 
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The equality v(+) = v(-) for an op-amp holds only while the op-amp is operating linearly and ouput is not saturated.

If those conditions are not met, then it's the case that
v(+) v(-)
 
Last edited:
Your feedback here is positive. In a linear noninverting amplifier the feedback is negative. BIG difference!

Use the fact that the op amp output is +12V if input V+ is higher than input V- , and -12V if V- > V+.

So you're always comparing input voltages V+ vs. V- as you vary the V- voltage back & forth. Hint: limit your V- input swing to +/- 0.2V.

The 10K output resistor limits the op amp output current to a safe value.
 

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