Op-amps that have the fixed trip points are either Tripped by voltage or current?

[danny davis]

The Op-amps that have the fixed trip points are either Tripped by
1.) The voltage level
2.) The Current Level

Are these Op-amp comparators? or are they something else

Because I can't tell when a Comparator is being tripped by a voltage level or a current level to trip the input so the op amps output switches states

How can you tell?

At work some Op-amps at tripped by a Fixed DC voltage of +10 volts , but it only tripped the input of the op-amp if you adjust the current to .300mA

The Op-amp won't trip if you adjust the voltage, it only trips when you apply a current level of .300mA

How can you tell when an Op-amp circuit or a comparator is tripped by current and not voltage?

Another thing I do at work is , I have to TIME how long the Op-amp or Comparator switches states from input to output, to measure how long it takes to trip the input and for the output to change switching states, What is this called what I am doing?

 

[barry]

How about a schematic? Your questions make no sense without some context.

Propagation delay is what you are trying to measure.

 

[danny davis]

No, it's not Propagation delay

Its the time difference between how fast the Op-amp comparator switches from input to output

 

[barry]

No, it's not Propagation delay

Its the time difference between how fast the Op-amp comparator switches from input to output

Then either I have no idea what you are talking about, or YOU have no idea what you are talking about. I'm assuming English is not your native language, so what EXACTLY do you mean by "comparator switches from input to output?"

 

[danny davis]

The comparator's input has a fixed voltage or current level that is FIXED . the output will switch from Zero volts ( millivolts ) to +10 volts

It takes TIME for the comparator to switch from zero volts to +10 volts , plus how much TIME it takes from input to output

 

[godfreyl]

Are these Op-amp comparators? or are they something else

They could be opamps or comparators or something else.
To find out, you need to look at the part number - either on the schematic or on the actual part.

How can you tell when an Op-amp circuit or a comparator is tripped by current and not voltage?

You need to look at the schematic and figure out how it works.

Then either I have no idea what you are talking about, or YOU have no idea what you are talking about.

Or both. I certainly don't. Maybe this is related to his other thread about RC delays.

 

[danny davis]

Comparators
1.) Voltage input Threshold
2.) Current input Threshold

I can't tell the difference between a voltage threshold VS a current threshold , when looking at a schematic that has comparators

1.) how can you tell if the input of a comparator has a Voltage threshold or a current threshold?
some comparators thresholds are triggered/tripped by a voltage level, other comparators are triggered/tripped by a current threshold

A Comparator that has a current threshold on it's input , will NOT switches the state of the comparators output if you apply a voltage from 1 volt to 20 volts on the input. It will only work if you apply a current that is higher than the threshold on it's input.

When looking at a schematic of comparators, how can you tell which comparators have a threshold that is for current and not a voltage threshold?

2.) Measure the time difference from a comparators input and output , to measure how long it takes for the comparators input threshold to be tripped to switches the comparators output
What is this called? its not slew rate or propagation delay , its a time measurement on how FAST the comparator switches the output compared from the threshold of the input

 

[Audioguru]

1) A comparator IC has a voltage input, not a current input. Therefore a comparator IC does not have a current threshold.
A series current sense resistor can be used to develop a voltage drop that can feed a comparator IC.

2) Why don't you look at the datasheet for an LM339 quad comparator IC to see a description and graphs of its "response time"?

 

[danny davis]

A series current sense resistor can be used to develop a voltage drop that can feed a comparator IC.

Isn't a current sense resistor use an Op amp? and a current sensor circuit it like a comparator circuit right?

comparator IC to see a description and graphs of its "response time"

How do you measure a comparators "response time" ? with an oscilloscope or in theory ? how can a test technician do this please?

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The LM339 comparator has a response time of 1.3uSec from the data sheets

response time is how quickly a comparator changes output based on an input change.

The call Response time also OVERDRIVE Input

 

[Audioguru]

Now you are quoting what was told to you in the other website forum.

 

[danny davis]

You typically measure the "response time" of a comparator between the input change and the output change with an oscilloscope.

How do you measure the time of just the Input change?

The Input can have an RC network to the input pin of the IC , so how do you measure the Input change time?

A comparator IS NOT an opamp but you are talking about both of them.

They are 741 op amps, used as a comparator, the inputs of the 741 op amps have a Voltage threshold

Since they aren't comparator IC chips , what is it called when you use an Op amp that has a voltage threshold or is compared with a fixed DC reference Input pin?

 

[Audioguru]

How do you measure the time of just the Input change?
The Input can have an RC network to the input pin of the IC , so how do you measure the Input change time?

The design of a 741 opamp is 46 years old so its switching response time is very slow. A resistor in series with its input and a capacitor parallel to the resistor boosts the speed of the signal to its input. Is that the RC network you talked about?

Since they aren't comparator IC chips , what is it called when you use an Op amp that has a voltage threshold or is compared with a fixed DC reference Input pin?

It is a slow opamp used as a slow comparator.

 

[danny davis]

A resistor in series with its input and a capacitor parallel to the resistor boosts the speed of the signal to its input. Is that the RC network you talked about?

Yes, How does it BOOST the speed of the signal going to the input? I don't get it

It is a slow opamp used as a slow comparator.

Why would they want a slow comparator? or a slow switching response time?

They are using a 741 op amp as an On/Off Switch right?

 

[Audioguru]

Maybe the circuits you are looking at are over 40 years old.

 

[danny davis]

they are from the 60's and 70's

They use 741 op amps as a switch or comparators , but they use RC networks on the input pins to cause delay or slow the switching response

Any reasons why?

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RC networks
1.) Resistor in series and cap in parallel grounded goes to input pin of 741 op amp ( as a switch or comparator )
2.) Cap in series and resistor in parallel goes to input pin of 741 op amp ( as a switch or comparator )
3.) Resistor tied to VCC and cap is parallel grounded goes to input pin of 741 op amp ( as a switch or comparator )

 

[Audioguru]

A series resistor then a capacitor to ground (or to the supply voltage) is a simple lowpass filter that causes a delay. (It is a lagging network)
A series resistor with a capacitor in parallel is a simple highpass filter. (It is a leading network)

 

[danny davis]

A series resistor then a capacitor to ground (or to the supply voltage) is a simple lowpass filter that causes a delay. (It is a lagging network)
A series resistor with a capacitor in parallel is a simple highpass filter. (It is a leading network)

Yes I know this, it's in my electronic book

But what is a Resistor tied to VCC and a capacitor tied to ground? The capacitor gets charged from the resistor tied to VCC , is this a lagging or leading network?

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A series capacitor with a resistor in parallel to ground ( is a lagging network)
A series resistor with a capacitor in parallel to ground ( is a leading network)

But what is a Resistor tied to VCC and a capacitor tied to ground? The capacitor gets charged from the resistor tied to VCC , is this a lagging or leading network?

Op amp output#1 goes to a Resistor tied to VCC with a capacitor tied to ground , the node that connects the resistor and capacitor goes to the input of Op amp#2

Op amp#1 output ----> goes to resistor tied to VCC with a cap tied to ground ----> Op amp#2 Input

The Resistor is tied to VCC is in parallel with the Op amps#1 output & Op amps#2 input , but so is the capacitor tied to ground is in parallel to Op amps#1 output and Op amp#2 input

Since the Resistor and capacitor are both in parallel , is this a lagging or leading network?

 

[Audioguru]

Since you do not know what you are talking about and do not post a schematic then we do not know what you are talking about.
You even copied WRONG the leading network.

 

[danny davis]

There is Two different kinds of comparators or op amps used as comparators:

COMPARATOR TYPE#1
1.) A Positive voltage that crosses the threshold limit on the input will make the Output of the comparator or op amp go HIGH
A Negative voltage that crosses the threshold limit on the input will make the Output of the comparator or op amp go LOW

I'm weird how the Positive voltage threshold value trip point is 5 volts , but the negative voltage threshold is like 2.5 volts
Not sure how they have two different threshold limits depending on the Polarity of the voltage

COMPARATOR TYPE#2
2.) Either Polarity, a Positive or Negative voltage will make the output go HIGH on the comparator or op amp

How can Either Polarity can cross the threshold voltage on the input and get a HIGH on the output?

Comparator type#1 , Positive polarity on input made output HIGH and Negative polarity on input made output LOW
Comparator type#2, Either positive or negative polarity will make the output HIGH

What I ran across was that the Positive and Negative polaritys threshold points were different

Positive Polarity at 5 volts made the comparator or op amp SWITCH to a HIGH state on the output
Negative Polarity at 3 volts made the comparator or op amp SWITCH to a HIGH state on the output

It's weird how the Positive polarity was 5 volts and the negative polarity was 3 volts

It seems like the comparator or op amp is off balanced when comparing

 

[Audioguru]

Please learn something about comparators, like learning about hysteresis that is added to a comparator circuit.