Trip Points either voltage or current levels to trip a comparator

[Billy Mayo]

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?

 

[crutschow]

I don't know what you mean by tripping on a current level. Post a circuit of that.

 

[Billy Mayo]

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

 

[Billy Mayo]

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

 

[Billy Mayo]

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

 

[crutschow]

...................................
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

1.) Most comparators are voltage sensitive. I have never seen a current comparator as you described. Post a circuit.

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

 

[audioguru]

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

A REAL comparator has voltage inputs, not current inputs. It cannot use negative feedback.

But an opamp can be inverting with negative feedback and can have a voltage input or a current input.

 

[Billy Mayo]

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]

See my reply on the other website forum.

 

[crutschow]

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?

.......................

You don't. The time is measured between when the input crosses the comparator threshold to the time the output changes state.

 

[Billy Mayo]

T

he time is measured between when the input crosses the comparator threshold to the time the output changes state.

Why does it cause a time delay? what is inside the comparator that is cause this? is it the slew rate?

the switching response time and the switching On/Off time of an op amp or comparator is causing a Time, what inside an opamp or comparator is causing this switching Delay? is this slew rate or something else?

 

[Billy Mayo]

I'm not sure what makes Inside an op amp or comparator a fast or slow switching Response?

I thought the RC network on the Input pin of a op amp or comparator would make the switching fast or slow, because RC is a time constant

 

[audioguru]

Have you ever looked at the schematic of an opamp on its datasheet? It has many transistors, each one causes some delay. Each small capacitance inside the IC causes some delay. An RC at the input can speed it a little or slow its response.

 

[Billy Mayo]

An RC at the input can speed it a little or slow its response.

How can it speed up the switching response?

So the Switching Response is the Slew rate?

Slew rate is the TIME delay from input and output of an IC op amp

 

[audioguru]

A series resistor always has some capacitance to ground at its distant end which causes some delay. A capacitor parallel to the resistor cancels the delay.

The switching response time is the time a signal travels from the input to the output of a circuit.
The slew rate is usually caused by the compensation capacitor in an opamp and/or the output transistors.

 

[Billy Mayo]

A series resistor always has some capacitance to ground at its distant end which causes some delay. A capacitor parallel to the resistor cancels the delay.

What capacitance to ground at it's distant end which causes some delay? do you mean the Op amps Input pin has an internal capacitance to ground internally?

A capacitors in parallel to the resistor cancels the delay? how? only if both capacitors are the same frequency

The switching response time is the time a signal travels from the input to the output of a circuit.

This is the Slew Rate, it's in micoseconds in the datasheets of an Op-amp

 

[audioguru]

What capacitance to ground at it's distant end which causes some delay? do you mean the Op amps Input pin has an internal capacitance to ground internally?

There is stray capacitance on every connection.

A capacitors in parallel to the resistor cancels the delay? how? only if both capacitors are the same frequency

The parallel capacitor is a leading network and the capacitor to ground is a lagging network. One can cancel the other.

This is the Slew Rate, it's in micoseconds in the datasheets of an Op-amp

No. The slew rate is not a time, it is an amount of voltage change. The switching response time is not the slew rate.
The slew rate is the voltage that the output can change in a microsecond. The slew is a slope because the output cannot swing a voltage quickly.

Since you did not learn anything about electronics then why don't you look up things in Google??

 

[Billy Mayo]

The parallel capacitor is a leading network and the capacitor to ground is a lagging network. One can cancel the other.

The parallel capacitor is the stray capacitance or the IC input internal capacitance?

 

[Billy Mayo]

The threshold voltage is at 5 volts
At work I have to test the iinput threshold , by testing the iinput threshold at both polaritys, positive input than use a negative input

if you apply a positive voltage it will switch the comparator or op amp at 4.9 volts

if you reverse the voltage to negative , it will switch the ccomparator or op amp at 3.2 volts

i don't understand why the comparator switches earlier when applying a negative voltage or current to the threshold input of a comparator or opamp

 

[Billy Mayo]

Why do i have to test the comparator iinput threshold at both Polaritys?

It seems that the comparator or op amp will switch not at the same voltage or current ddepending on the polarity of the input voltage or current

wwhy does the inputs polarity change the threshold switching?