# Question about bistable multivibrator op amps

• theBEAST
In summary, the conversation discusses a bistable multivibrator and the use of KVL and KCL laws in circuit analysis. The solution is described as the input voltage caps at 0.1V and the output caps at 0.7V, causing hysteresis. The conversation also mentions the role of feedback in the operation of an op-amp, and how it differs in a linear noninverting amplifier compared to a bistable multivibrator. The significance of the 10k resistor in the circuit is also explained.
theBEAST

## Homework Statement

Here is the problem:

So this is a bistable multivibrator.

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:

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?

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.

## 1. What is a bistable multivibrator op amp?

A bistable multivibrator op amp is a circuit that has two stable states and can switch between them based on input signals. It is used in applications where a digital output is required, such as in flip-flops and counters.

## 2. How does a bistable multivibrator op amp work?

In a bistable multivibrator op amp, the two stable states are created by two transistors that are cross-coupled. When one transistor is conducting, the other is cut off, and vice versa. The circuit is designed to switch states when a trigger signal is received, causing the output to change.

## 3. What are the applications of bistable multivibrator op amps?

Bistable multivibrator op amps are commonly used in digital circuits, such as in flip-flops and counters, to store and process binary data. They can also be used in pulse generators, oscillators, and other timing circuits.

## 4. What are the advantages of using bistable multivibrator op amps?

One advantage of using bistable multivibrator op amps is their simplicity, as they require only a few components and can be easily integrated into larger circuits. They also have a high immunity to noise and can operate at high speeds, making them useful in digital applications.

## 5. Are there any limitations to using bistable multivibrator op amps?

One limitation of bistable multivibrator op amps is that they can only operate at two stable states, which may not be suitable for all applications. They also require a stable power supply and can be affected by temperature changes. Additionally, the output may not be as precise as other types of op amps.

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