Why would you want Comparators outputs to Oscillate?

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danny davis

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At my job the circuits WANT the comparators outputs to oscillate? why would you want a comparator to oscillate?

I know they add a Stabilization Capacitor on pin#1 and pin#8 when they DON"T want to have a comparator to oscillate

How does a stabilization capacitor work? how does it stabilize the comparator not to oscillate?
 

Re: Comparators outputs Oscillate

The output of a comparator should switch high or low and should not oscillate. Hysteresis is added to prevent oscillation when its input is near its threshold voltage.
You forgot to say which comparator part number you are talking about and did not provide a schematic of the circuit.
 

Re: Comparators outputs Oscillate

It's an Op-amp , i will get the name of it LM241 I think it's not LM741 i know for sure

But they use they add a Stabilization Capacitor on pin#1 and pin#8 when they DON"T want to have a comparator to oscillate

They Don't use Hysteresis , they use a Stabilization Capacitor

It's an op amp used as a comparator

Why would anyone what a comparator to have an output to oscillate? for what reason?
 

Re: Comparators outputs Oscillate

A comparator is COMPLETELY DIFFERENT to an opamp. Why do you confuse the two?
A very, very, very, very old opamp such as an LM101, LM201 or LM301 had an external compensation capacitor between pin 1 and pin 8. Nearly ALL more modern opamps beginning with the 741 opamp have it built-in.

You never learned anything about opamps. Learn about them now.
 

Re: Comparators outputs Oscillate

LM101, LM201 or LM301 had an external compensation capacitor between pin 1 and pin 8.
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I'm going to work on monday to check the name of the IC chip but they do use a lot of LM101 IC chip , which i think it is , it is an op-amp used as a comparator

I know what an external compensation capacitor is , it has nothing to do with this, it's totally different

The writers of the service manual call it a Stabilization Capacitor which Doesn't make the output of the comparator oscillate
its from pin#1 to pin#8

But they Also use Comparators without the Stablization capacitor because the WANT the comparator to Oscillate, Why would anyone want a comparator to oscillate? what does it do when it's oscillating? it's at a frequency
 

Re: Comparators outputs Oscillate

danny davis said:
...they Also use Comparators without the Stablization capacitor because the WANT the comparator to Oscillate, Why would anyone want a comparator to oscillate? what does it do when it's oscillating? it's at a frequency
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In a simplified viewpoint Comparators are designed to operate at open-loop circuits or positive feed-back gain topologies such as oscilators, whereas Operational Amplifiers are designed to operate at steady state closed-loop circuits, which requires stabilization, otherwise would oscillate.


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Re: Comparators outputs Oscillate

Operational Amplifiers are designed to operate at steady state closed-loop circuits, which requires stabilization, otherwise would oscillate.
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Why would you want a comparator to oscillate?

What's the different between an Op amp amplifier oscillating VS an closed Loop circuit Op-amp comparator Oscillating? what do they do different?
 

Re: Comparators outputs Oscillate

Op amp amplifiers are not suitable to work as oscillators, due their intrinsic structure is somewhat a little more complex, and internally has a built in stabilization capacitor, placed just for avoid exhibit some small oscillation around steady point.


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Re: Comparators outputs Oscillate

internally has a built in stabilization capacitor
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Not the LM101, 102, 103, we do use these at work, and you have to put a capacitor from Pin#1 to Pin#8

Op amp amplifiers are not suitable to work as oscillators,
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Yes but their output can oscillate, or have an oscillating output
 

Re: Comparators outputs Oscillate

Without the external compensation capacitor, an old LM101 opamp makes a pretty good comparator. Without the compensation capacitor it will not oscillate if its circuit layout is good, if it has no negative feedback and has some hysteresis.

"Stabilization capacitor" or "compensation capacitor" are the same thing. The capacitor reduces the gain to less than 1 at the high frequency that the phase shift causes oscillation when it has negative feedback.
 

Re: Comparators outputs Oscillate

Without the compensation capacitor it will not oscillate if its circuit layout is good, if it has no negative feedback and has some hysteresis.
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It says in the service manual under the Theory of operations of the circuit and it explains that the LM101 op amp is figured as a comparator and the output does oscillate , they use a comparator to oscillate

My question is why would they want a comparator to oscillate? how it is different than an oscillator IC chip or an oscillator circuit

I still don't understand how hysteresis can fix or prevent an output from oscillating or to oscillate

"Stabilization capacitor" or "compensation capacitor" are the same thing. The capacitor reduces the gain to less than 1 at the high frequency that the phase shift causes oscillation when it has negative feedback.
Click to expand...

That's a compensation capacitor , that's for AC input signals and AC output signals

A Stabilization capacitor is for DC input signals and DC output signals

It is the way thing but it's for different applications

IT's like amplitude and magnitude , some people say it's the say things , I think they are different

Magnitude is for phase angle voltage or phase shift voltage, amplitude is voltage that has no phase shift
 

Re: Comparators outputs Oscillate

An LM101 opamp without a compensation or stabilization capacitor will oscillate at the high frequency where its internal phase shift combines with negative feedback even when it is a DC amplifier with a steady DC input.

Danny, Billy or Walters:
IT IS USELESS TALKING TO YOU BECAUSE YOU DO NOT UNDERSTAND BASIC ELECTRONICS and common English. The same as on the other website that banned you.
 

Re: Comparators outputs Oscillate

An LM101 opamp without a compensation or stabilization capacitor will oscillate at the high frequency where its internal phase shift combines with negative feedback even when it is a DC amplifier with a steady DC input.
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Why does it oscillate even as a DC amplifier? with a steady DC input?

How can the output oscillate when the input is a steady DC input, i don't get it
 

Re: Comparators outputs Oscillate

See, YOU DO NOT GET IT with anything in electronics because you never learned electronics.

An opamp has TWO inputs. The negative input is used for negative feedback that becomes positive feedback at a high frequency due to internal phase shift. Positive feedback at a high frequency causes it to oscillate.
That is why an opamp uses a compensation capacitor to make it stable (it can also be called a stabilization capacitor) when it has negative feedback.

An oscillator has a steady DC input. It also has frequency-selective positive feedback.
 

Re: Comparators outputs Oscillate

An oscillator has a steady DC input.
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I thought an oscillator had a AC output waveform that is feedback to the input pin

or an oscillator has a swinging charging and discharging output and is feedback to the input pin

I'm not sure about an oscillator having a steady DC input and DC output

The negative input is used for negative feedback that becomes positive feedback at a high frequency due to internal phase shift.
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You're saying that the negative feedback that goes from the Op-amp input pin to the output pin gets converted internally inside the op-amp from negative feedback to positive feedback?

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When a comparator is oscillating , what is different about the oscillation than an oscillator circuit?

It seems that when a comparators output is oscillating or in oscillation it is Irregular and random I'm guessing , the swinging of oscillation

An Oscillator circuit output oscillating is stable and fixed and regular
 

Re: Comparators outputs Oscillate

danny davis said:
...How can the output oscillate when the input is a steady DC input, i don't get it
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Maybe you´re getting confused about term "oscillating", which is mostly applied to a design purposed for that.

What we´re trying to explain is that when a comparator is used at loop-back circuit, even having an overall gain less that 1, occurs a little swing of bias voltage around steady point, due to it attempt to converge to the central point, but once reaches every time ( because is not damped for any compensation capacitor ). This called "oscillation" happens at a very fast speed because Comparators are not compensated.


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Re: Comparators outputs Oscillate

Why are people using a srew-wrench to open a bottle of beer?
- because they don't have a bottle opener
- because they just like to

The method is however known to work and it's a bit pointless to ask why people are doing it. Exactly the same with the oscillating comparator, I think.
 

Re: Comparators outputs Oscillate

danny davis said:
My question is why would they want a comparator to oscillate? how it is different than an oscillator IC chip or an oscillator circuit
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danny, who wants a comparator to oscillate? Who is "they"? Please, can you repeat the corresponding sentences from the document you are speaking of?
By the way: If somebody speaks about a dc input for an oscillator circuit he certainly means the power supply or biasing circuitry (single supply). No other dc input needed.
 

Re: Comparators outputs Oscillate

biasing circuitry
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What is the biasing circuit of an oscillator? what do u mean?


Why is there a swing of bias voltage around steady point? where does this bias voltage come from?

Why does a comparator need to be compensated? to prevent oscillation? because of the GAIN?

I thought a comparator was a DC amplifier or DC switching function block , it's not an amplifier function block or has gain
 

Re: Comparators outputs Oscillate


It is becoming apparent that some classic concepts you are missing on scope of analog control and internal structure of Op Amp.
Unless you get this knowledge base will be difficult to answer all your questions so deep without new questions are being raised recursively.


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