Operational amplifier as a comparator at high frequencyReasons not to use a 741 op-amp?Can I use LM324 as a Schmitt trigger?Simple op-amp differential amplifierOp amp has a biased outputReduced output of op amp peak detection and hold circuitHow to select the right Operational Amplifier as an impedance converter?Bias voltage of non-inverting op amplifier drops to 0 when input signal connectedHigh negative voltages with op-ampopamp output unstableComparator circuit undesirable fluctuations20kHz sine wave signal amplificationIf there exists a cascade of op amps, does the previous op amp's slew rate affect the later op amp's slew rates?
Can a German sentence have two subjects?
What do you call something that goes against the spirit of the law, but is legal when interpreting the law to the letter?
I probably found a bug with the sudo apt install function
N.B. ligature in Latex
Extreme, but not acceptable situation and I can't start the work tomorrow morning
Do airline pilots ever risk not hearing communication directed to them specifically, from traffic controllers?
Why do we use polarized capacitor?
How old can references or sources in a thesis be?
Why Is Death Allowed In the Matrix?
Why doesn't Newton's third law mean a person bounces back to where they started when they hit the ground?
What does "enim et" mean?
Why is an old chain unsafe?
Is it legal to have the "// (c) 2019 John Smith" header in all files when there are hundreds of contributors?
What makes Graph invariants so useful/important?
What is GPS' 19 year rollover and does it present a cybersecurity issue?
What would happen to a modern skyscraper if it rains micro blackholes?
Why CLRS example on residual networks does not follows its formula?
What defenses are there against being summoned by the Gate spell?
Why did the Germans forbid the possession of pet pigeons in Rostov-on-Don in 1941?
What is the command to reset a PC without deleting any files
How do you conduct xenoanthropology after first contact?
Accidentally leaked the solution to an assignment, what to do now? (I'm the prof)
Copycat chess is back
How is it possible for user's password to be changed after storage was encrypted? (on OS X, Android)
Operational amplifier as a comparator at high frequency
Reasons not to use a 741 op-amp?Can I use LM324 as a Schmitt trigger?Simple op-amp differential amplifierOp amp has a biased outputReduced output of op amp peak detection and hold circuitHow to select the right Operational Amplifier as an impedance converter?Bias voltage of non-inverting op amplifier drops to 0 when input signal connectedHigh negative voltages with op-ampopamp output unstableComparator circuit undesirable fluctuations20kHz sine wave signal amplificationIf there exists a cascade of op amps, does the previous op amp's slew rate affect the later op amp's slew rates?
.everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty margin-bottom:0;
$begingroup$
I am trying to generate a sinusoidal PWM signal using analog circuits.
I want to compare my sine wave and triangular wave using an operational amplifier (LM741) which has a rise time of 0.3 µs and slew rate 0.5 V/µs, which will good at 5 kHz theoretically. But I am not getting a good PWM output.
So I first tried to compare the sine wave with a reference voltage (2.2 volt). Sine wave amplitude = 2.5 volt (5 V peak to peak) and frequency 100 Hz and 5 kHz.
- At low frequency (say 100 Hz), the output is good
- At high frequency (say 5 kHz), the output is too bad.
What will be the problem...
If the response is the problem of the comparator, but the slew rate is 0.5 V/µs.
Calculation of slew rate for a sinusoidal signal...
Slew rate= Vm * 2pi * Frequency
= 5 V * 2pi* 5000 Hz
= 1570796 volt per second or 0.15 V/µs
Theoretically the slew rate of 0.5 V/µs will be OK for a sinusoidal signal of 5 kHz and 5 volt peak to peak. But in my case the signal is distorted.
Where am I wrong?
operational-amplifier comparator
edited 2 days ago
Peter Mortensen
1,60031422
asked 2 days ago
NihalNihal
518
$endgroup$
|
show 2 more comments
$begingroup$
I am trying to generate a sinusoidal PWM signal using analog circuits.
I want to compare my sine wave and triangular wave using an operational amplifier (LM741) which has a rise time of 0.3 µs and slew rate 0.5 V/µs, which will good at 5 kHz theoretically. But I am not getting a good PWM output.
So I first tried to compare the sine wave with a reference voltage (2.2 volt). Sine wave amplitude = 2.5 volt (5 V peak to peak) and frequency 100 Hz and 5 kHz.
- At low frequency (say 100 Hz), the output is good
- At high frequency (say 5 kHz), the output is too bad.
What will be the problem...
If the response is the problem of the comparator, but the slew rate is 0.5 V/µs.
Calculation of slew rate for a sinusoidal signal...
Slew rate= Vm * 2pi * Frequency
= 5 V * 2pi* 5000 Hz
= 1570796 volt per second or 0.15 V/µs
Theoretically the slew rate of 0.5 V/µs will be OK for a sinusoidal signal of 5 kHz and 5 volt peak to peak. But in my case the signal is distorted.
Where am I wrong?
operational-amplifier comparator
edited 2 days ago
Peter Mortensen
1,60031422
asked 2 days ago
NihalNihal
518
$endgroup$
$begingroup$
It looks like there's a significant lag/delay in the output's response w.r.t. the input signal (~30µs?). What may be causing this? What's connected to the output? 'Scope probe only?
$endgroup$
– JimmyB
2 days ago
5
$begingroup$
Why you shouldn't use the 741.
$endgroup$
– JRE
2 days ago
$begingroup$
For 5Khz i thought 741 will be ok, for what i calculated .Orelse sure i will change the opp amp which having high slew rate and i will update it.......@JRE
$endgroup$
– Nihal
2 days ago
1
$begingroup$
You're latching up.
$endgroup$
– Scott Seidman
2 days ago
1
$begingroup$
Note that this question is about the theory behind the calculations. Telling OP to change his OP-amp does nothing to answer the question. It just solves the problem without OP knowing why.
$endgroup$
– pipe
2 days ago
|
show 2 more comments
$begingroup$
I am trying to generate a sinusoidal PWM signal using analog circuits.
I want to compare my sine wave and triangular wave using an operational amplifier (LM741) which has a rise time of 0.3 µs and slew rate 0.5 V/µs, which will good at 5 kHz theoretically. But I am not getting a good PWM output.
So I first tried to compare the sine wave with a reference voltage (2.2 volt). Sine wave amplitude = 2.5 volt (5 V peak to peak) and frequency 100 Hz and 5 kHz.
- At low frequency (say 100 Hz), the output is good
- At high frequency (say 5 kHz), the output is too bad.
What will be the problem...
If the response is the problem of the comparator, but the slew rate is 0.5 V/µs.
Calculation of slew rate for a sinusoidal signal...
Slew rate= Vm * 2pi * Frequency
= 5 V * 2pi* 5000 Hz
= 1570796 volt per second or 0.15 V/µs
Theoretically the slew rate of 0.5 V/µs will be OK for a sinusoidal signal of 5 kHz and 5 volt peak to peak. But in my case the signal is distorted.
Where am I wrong?
operational-amplifier comparator
edited 2 days ago
Peter Mortensen
1,60031422
asked 2 days ago
NihalNihal
518
$endgroup$
I am trying to generate a sinusoidal PWM signal using analog circuits.
I want to compare my sine wave and triangular wave using an operational amplifier (LM741) which has a rise time of 0.3 µs and slew rate 0.5 V/µs, which will good at 5 kHz theoretically. But I am not getting a good PWM output.
So I first tried to compare the sine wave with a reference voltage (2.2 volt). Sine wave amplitude = 2.5 volt (5 V peak to peak) and frequency 100 Hz and 5 kHz.
- At low frequency (say 100 Hz), the output is good
- At high frequency (say 5 kHz), the output is too bad.
What will be the problem...
If the response is the problem of the comparator, but the slew rate is 0.5 V/µs.
Calculation of slew rate for a sinusoidal signal...
Slew rate= Vm * 2pi * Frequency
= 5 V * 2pi* 5000 Hz
= 1570796 volt per second or 0.15 V/µs
Theoretically the slew rate of 0.5 V/µs will be OK for a sinusoidal signal of 5 kHz and 5 volt peak to peak. But in my case the signal is distorted.
Where am I wrong?
operational-amplifier comparator
operational-amplifier comparator
edited 2 days ago
Peter Mortensen
1,60031422
asked 2 days ago
NihalNihal
518
edited 2 days ago
Peter Mortensen
1,60031422
asked 2 days ago
NihalNihal
518
edited 2 days ago
Peter Mortensen
1,60031422
edited 2 days ago
Peter Mortensen
1,60031422
edited 2 days ago
Peter Mortensen
1,60031422
1,60031422
asked 2 days ago
NihalNihal
518
asked 2 days ago
NihalNihal
518
asked 2 days ago
NihalNihal
518
518
$begingroup$
It looks like there's a significant lag/delay in the output's response w.r.t. the input signal (~30µs?). What may be causing this? What's connected to the output? 'Scope probe only?
$endgroup$
– JimmyB
2 days ago
5
$begingroup$
Why you shouldn't use the 741.
$endgroup$
– JRE
2 days ago
$begingroup$
For 5Khz i thought 741 will be ok, for what i calculated .Orelse sure i will change the opp amp which having high slew rate and i will update it.......@JRE
$endgroup$
– Nihal
2 days ago
1
$begingroup$
You're latching up.
$endgroup$
– Scott Seidman
2 days ago
1
$begingroup$
Note that this question is about the theory behind the calculations. Telling OP to change his OP-amp does nothing to answer the question. It just solves the problem without OP knowing why.
$endgroup$
– pipe
2 days ago
|
show 2 more comments
$begingroup$
It looks like there's a significant lag/delay in the output's response w.r.t. the input signal (~30µs?). What may be causing this? What's connected to the output? 'Scope probe only?
$endgroup$
– JimmyB
2 days ago
5
$begingroup$
Why you shouldn't use the 741.
$endgroup$
– JRE
2 days ago
$begingroup$
For 5Khz i thought 741 will be ok, for what i calculated .Orelse sure i will change the opp amp which having high slew rate and i will update it.......@JRE
$endgroup$
– Nihal
2 days ago
1
$begingroup$
You're latching up.
$endgroup$
– Scott Seidman
2 days ago
1
$begingroup$
Note that this question is about the theory behind the calculations. Telling OP to change his OP-amp does nothing to answer the question. It just solves the problem without OP knowing why.
$endgroup$
– pipe
2 days ago
$begingroup$
It looks like there's a significant lag/delay in the output's response w.r.t. the input signal (~30µs?). What may be causing this? What's connected to the output? 'Scope probe only?
$endgroup$
– JimmyB
2 days ago
$begingroup$
It looks like there's a significant lag/delay in the output's response w.r.t. the input signal (~30µs?). What may be causing this? What's connected to the output? 'Scope probe only?
$endgroup$
– JimmyB
2 days ago
5
5
$begingroup$
Why you shouldn't use the 741.
$endgroup$
– JRE
2 days ago
$begingroup$
Why you shouldn't use the 741.
$endgroup$
– JRE
2 days ago
$begingroup$
For 5Khz i thought 741 will be ok, for what i calculated .Orelse sure i will change the opp amp which having high slew rate and i will update it.......@JRE
$endgroup$
– Nihal
2 days ago
$begingroup$
For 5Khz i thought 741 will be ok, for what i calculated .Orelse sure i will change the opp amp which having high slew rate and i will update it.......@JRE
$endgroup$
– Nihal
2 days ago
1
1
$begingroup$
You're latching up.
$endgroup$
– Scott Seidman
2 days ago
$begingroup$
You're latching up.
$endgroup$
– Scott Seidman
2 days ago
1
1
$begingroup$
Note that this question is about the theory behind the calculations. Telling OP to change his OP-amp does nothing to answer the question. It just solves the problem without OP knowing why.
$endgroup$
– pipe
2 days ago
$begingroup$
Note that this question is about the theory behind the calculations. Telling OP to change his OP-amp does nothing to answer the question. It just solves the problem without OP knowing why.
$endgroup$
– pipe
2 days ago
|
show 2 more comments
5 Answers
5
active
oldest
votes
$begingroup$
The recommendations for you are very simple.
Use a comparator for this application instead of an opamp.
Select a newer part that operates with orders of magnitude faster response time.
It would be the very best thing if the 741 could be eradicated from face of the earth.
Here is what can be achieved with the venerable LM393 at 5kHz. The shown circuit will work even up to about 50kHz before the delay of the LM393 starts to distort the PWM duty cycle.
answered 2 days ago
Michael KarasMichael Karas
45.2k348105
$endgroup$
$begingroup$
Sure friend i will change the opp amp or by using comparator, i will update the data soon.
$endgroup$
– Nihal
2 days ago
1
$begingroup$
@Nihal - If you show some new results in the question do not delete your original material, Instead add it as an update at the end. The reason for this is that hopefully this question can be a reference to future readers that are looking for information as being discussed here. If you delete the original material the answers here would no longer make much sense to a future reader.
$endgroup$
– Michael Karas
2 days ago
1
$begingroup$
"It would be the very best thing if the 741 could be eradicated from face of the earth." ok - I'll bite. what's your reasons?
$endgroup$
– UKMonkey
2 days ago
2
$begingroup$
@UKMonkey the 741 was first released in 1968. And while it was a fantastic IC at the time, there are vastly superior op-amps available with lower input offset voltage, higher bandwidth, higher input impedance, etc. Most people lean the "ideal op-amp" first, and then immediately jump to one of the most non-ideal op-amps in practice, and wonder why their design doesn't work.
$endgroup$
– CurtisHx
2 days ago
$begingroup$
LM741 might still be in the textbooks...
$endgroup$
– Peter Mortensen
2 days ago
|
show 7 more comments
$begingroup$
Opamps work slowly with low power supply voltages. In addition they are designed to work in linear region. As saturated, like in your application, the response has an unpredictable dead time. before the internal saturation is vanished.
I can only repeat what's already said: Get a comparator. 741 was a remarkable step forward half a century ago, but things have developed better since those days.
answered 2 days ago
user287001user287001
9,6791517
$endgroup$
$begingroup$
Thank you for your response friend, i will update it after changing the opp amp.
$endgroup$
– Nihal
2 days ago
2
$begingroup$
@Nihal Comparators have other precautions. They are high speed circuits like logic parts. You must have acceptably short wires and coupling capacitors between supply voltage inputs. Making the circuit with 0,5 meter long wires onto a breadboard without coupling caps (I have seen those attempts) will be useless.
$endgroup$
– user287001
2 days ago
$begingroup$
Ok friend I will even buy a comparator and I will check with it.
$endgroup$
– Nihal
2 days ago
add a comment |
$begingroup$
Op-amps are susceptible to latch-up. Recovering from saturation at the rails is not an automatic thing. The ratings you are reading a for the op amp working in a feedback mode, not an open loop mode. You would need to find an op amp designed to minimize latch-up, or better yet, when you need a comparator, buy a comparator.
answered 2 days ago
Scott SeidmanScott Seidman
22.7k43286
$endgroup$
1
$begingroup$
Yes, and/or phase inversion, depending on the op-amp type.
$endgroup$
– Peter Mortensen
2 days ago
add a comment |
$begingroup$
You may try this, if you want a discrete solution
simulate this circuit – Schematic created using CircuitLab
The speed will be limited by Rin (10Kohm) and Miller Effect Cin (100pF?), thus propagation delay will be about 1 uS.
answered 2 days ago
analogsystemsrfanalogsystemsrf
16k2822
$endgroup$
$begingroup$
What is it? A Schmitt trigger?
$endgroup$
– Peter Mortensen
2 days ago
$begingroup$
The differential pair is biased at VDD/2. R8 does provide 1% positive feedback, to reduce the risk of oscillation during the linear region. Notice I included over-voltage protection.
$endgroup$
– analogsystemsrf
2 days ago
add a comment |
$begingroup$
Most garden variety op-amps have internal compensation in the form of a chip capacitor.
This makes them very slow, but more stable in analog circuits.
Why not use a cheap comparator like LM393?
edited 2 days ago
Renan
4,32222244
answered 2 days ago
AutisticAutistic
7,50921633
$endgroup$
add a comment |
Your Answer
StackExchange.ifUsing("editor", function ()
return StackExchange.using("mathjaxEditing", function ()
StackExchange.MarkdownEditor.creationCallbacks.add(function (editor, postfix)
StackExchange.mathjaxEditing.prepareWmdForMathJax(editor, postfix, [["\$", "\$"]]);
);
);
, "mathjax-editing");
StackExchange.ifUsing("editor", function ()
return StackExchange.using("schematics", function ()
StackExchange.schematics.init();
);
, "cicuitlab");
StackExchange.ready(function()
var channelOptions =
tags: "".split(" "),
id: "135"
;
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function()
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled)
StackExchange.using("snippets", function()
createEditor();
);
else
createEditor();
);
function createEditor()
StackExchange.prepareEditor(
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: false,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: null,
bindNavPrevention: true,
postfix: "",
imageUploader:
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
,
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
);
);
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function ()
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2felectronics.stackexchange.com%2fquestions%2f430885%2foperational-amplifier-as-a-comparator-at-high-frequency%23new-answer', 'question_page');
);
Post as a guest
Required, but never shown
5 Answers
5
active
oldest
votes
5 Answers
5
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
The recommendations for you are very simple.
Use a comparator for this application instead of an opamp.
Select a newer part that operates with orders of magnitude faster response time.
It would be the very best thing if the 741 could be eradicated from face of the earth.
Here is what can be achieved with the venerable LM393 at 5kHz. The shown circuit will work even up to about 50kHz before the delay of the LM393 starts to distort the PWM duty cycle.
answered 2 days ago
Michael KarasMichael Karas
45.2k348105
$endgroup$
$begingroup$
Sure friend i will change the opp amp or by using comparator, i will update the data soon.
$endgroup$
– Nihal
2 days ago
1
$begingroup$
@Nihal - If you show some new results in the question do not delete your original material, Instead add it as an update at the end. The reason for this is that hopefully this question can be a reference to future readers that are looking for information as being discussed here. If you delete the original material the answers here would no longer make much sense to a future reader.
$endgroup$
– Michael Karas
2 days ago
1
$begingroup$
"It would be the very best thing if the 741 could be eradicated from face of the earth." ok - I'll bite. what's your reasons?
$endgroup$
– UKMonkey
2 days ago
2
$begingroup$
@UKMonkey the 741 was first released in 1968. And while it was a fantastic IC at the time, there are vastly superior op-amps available with lower input offset voltage, higher bandwidth, higher input impedance, etc. Most people lean the "ideal op-amp" first, and then immediately jump to one of the most non-ideal op-amps in practice, and wonder why their design doesn't work.
$endgroup$
– CurtisHx
2 days ago
$begingroup$
LM741 might still be in the textbooks...
$endgroup$
– Peter Mortensen
2 days ago
|
show 7 more comments
$begingroup$
The recommendations for you are very simple.
Use a comparator for this application instead of an opamp.
Select a newer part that operates with orders of magnitude faster response time.
It would be the very best thing if the 741 could be eradicated from face of the earth.
Here is what can be achieved with the venerable LM393 at 5kHz. The shown circuit will work even up to about 50kHz before the delay of the LM393 starts to distort the PWM duty cycle.
answered 2 days ago
Michael KarasMichael Karas
45.2k348105
$endgroup$
$begingroup$
Sure friend i will change the opp amp or by using comparator, i will update the data soon.
$endgroup$
– Nihal
2 days ago
1
$begingroup$
@Nihal - If you show some new results in the question do not delete your original material, Instead add it as an update at the end. The reason for this is that hopefully this question can be a reference to future readers that are looking for information as being discussed here. If you delete the original material the answers here would no longer make much sense to a future reader.
$endgroup$
– Michael Karas
2 days ago
1
$begingroup$
"It would be the very best thing if the 741 could be eradicated from face of the earth." ok - I'll bite. what's your reasons?
$endgroup$
– UKMonkey
2 days ago
2
$begingroup$
@UKMonkey the 741 was first released in 1968. And while it was a fantastic IC at the time, there are vastly superior op-amps available with lower input offset voltage, higher bandwidth, higher input impedance, etc. Most people lean the "ideal op-amp" first, and then immediately jump to one of the most non-ideal op-amps in practice, and wonder why their design doesn't work.
$endgroup$
– CurtisHx
2 days ago
$begingroup$
LM741 might still be in the textbooks...
$endgroup$
– Peter Mortensen
2 days ago
|
show 7 more comments
$begingroup$
The recommendations for you are very simple.
Use a comparator for this application instead of an opamp.
Select a newer part that operates with orders of magnitude faster response time.
It would be the very best thing if the 741 could be eradicated from face of the earth.
Here is what can be achieved with the venerable LM393 at 5kHz. The shown circuit will work even up to about 50kHz before the delay of the LM393 starts to distort the PWM duty cycle.
answered 2 days ago
Michael KarasMichael Karas
45.2k348105
$endgroup$
The recommendations for you are very simple.
Use a comparator for this application instead of an opamp.
Select a newer part that operates with orders of magnitude faster response time.
It would be the very best thing if the 741 could be eradicated from face of the earth.
Here is what can be achieved with the venerable LM393 at 5kHz. The shown circuit will work even up to about 50kHz before the delay of the LM393 starts to distort the PWM duty cycle.
answered 2 days ago
Michael KarasMichael Karas
45.2k348105
edited 2 days ago
answered 2 days ago
Michael KarasMichael Karas
45.2k348105
answered 2 days ago
Michael KarasMichael Karas
45.2k348105
answered 2 days ago
Michael KarasMichael Karas
45.2k348105
45.2k348105
$begingroup$
Sure friend i will change the opp amp or by using comparator, i will update the data soon.
$endgroup$
– Nihal
2 days ago
1
$begingroup$
@Nihal - If you show some new results in the question do not delete your original material, Instead add it as an update at the end. The reason for this is that hopefully this question can be a reference to future readers that are looking for information as being discussed here. If you delete the original material the answers here would no longer make much sense to a future reader.
$endgroup$
– Michael Karas
2 days ago
1
$begingroup$
"It would be the very best thing if the 741 could be eradicated from face of the earth." ok - I'll bite. what's your reasons?
$endgroup$
– UKMonkey
2 days ago
2
$begingroup$
@UKMonkey the 741 was first released in 1968. And while it was a fantastic IC at the time, there are vastly superior op-amps available with lower input offset voltage, higher bandwidth, higher input impedance, etc. Most people lean the "ideal op-amp" first, and then immediately jump to one of the most non-ideal op-amps in practice, and wonder why their design doesn't work.
$endgroup$
– CurtisHx
2 days ago
$begingroup$
LM741 might still be in the textbooks...
$endgroup$
– Peter Mortensen
2 days ago
|
show 7 more comments
$begingroup$
Sure friend i will change the opp amp or by using comparator, i will update the data soon.
$endgroup$
– Nihal
2 days ago
1
$begingroup$
@Nihal - If you show some new results in the question do not delete your original material, Instead add it as an update at the end. The reason for this is that hopefully this question can be a reference to future readers that are looking for information as being discussed here. If you delete the original material the answers here would no longer make much sense to a future reader.
$endgroup$
– Michael Karas
2 days ago
1
$begingroup$
"It would be the very best thing if the 741 could be eradicated from face of the earth." ok - I'll bite. what's your reasons?
$endgroup$
– UKMonkey
2 days ago
2
$begingroup$
@UKMonkey the 741 was first released in 1968. And while it was a fantastic IC at the time, there are vastly superior op-amps available with lower input offset voltage, higher bandwidth, higher input impedance, etc. Most people lean the "ideal op-amp" first, and then immediately jump to one of the most non-ideal op-amps in practice, and wonder why their design doesn't work.
$endgroup$
– CurtisHx
2 days ago
$begingroup$
LM741 might still be in the textbooks...
$endgroup$
– Peter Mortensen
2 days ago
$begingroup$
Sure friend i will change the opp amp or by using comparator, i will update the data soon.
$endgroup$
– Nihal
2 days ago
$begingroup$
Sure friend i will change the opp amp or by using comparator, i will update the data soon.
$endgroup$
– Nihal
2 days ago
1
1
$begingroup$
@Nihal - If you show some new results in the question do not delete your original material, Instead add it as an update at the end. The reason for this is that hopefully this question can be a reference to future readers that are looking for information as being discussed here. If you delete the original material the answers here would no longer make much sense to a future reader.
$endgroup$
– Michael Karas
2 days ago
$begingroup$
@Nihal - If you show some new results in the question do not delete your original material, Instead add it as an update at the end. The reason for this is that hopefully this question can be a reference to future readers that are looking for information as being discussed here. If you delete the original material the answers here would no longer make much sense to a future reader.
$endgroup$
– Michael Karas
2 days ago
1
1
$begingroup$
"It would be the very best thing if the 741 could be eradicated from face of the earth." ok - I'll bite. what's your reasons?
$endgroup$
– UKMonkey
2 days ago
$begingroup$
"It would be the very best thing if the 741 could be eradicated from face of the earth." ok - I'll bite. what's your reasons?
$endgroup$
– UKMonkey
2 days ago
2
2
$begingroup$
@UKMonkey the 741 was first released in 1968. And while it was a fantastic IC at the time, there are vastly superior op-amps available with lower input offset voltage, higher bandwidth, higher input impedance, etc. Most people lean the "ideal op-amp" first, and then immediately jump to one of the most non-ideal op-amps in practice, and wonder why their design doesn't work.
$endgroup$
– CurtisHx
2 days ago
$begingroup$
@UKMonkey the 741 was first released in 1968. And while it was a fantastic IC at the time, there are vastly superior op-amps available with lower input offset voltage, higher bandwidth, higher input impedance, etc. Most people lean the "ideal op-amp" first, and then immediately jump to one of the most non-ideal op-amps in practice, and wonder why their design doesn't work.
$endgroup$
– CurtisHx
2 days ago
$begingroup$
LM741 might still be in the textbooks...
$endgroup$
– Peter Mortensen
2 days ago
$begingroup$
LM741 might still be in the textbooks...
$endgroup$
– Peter Mortensen
2 days ago
|
show 7 more comments
$begingroup$
Opamps work slowly with low power supply voltages. In addition they are designed to work in linear region. As saturated, like in your application, the response has an unpredictable dead time. before the internal saturation is vanished.
I can only repeat what's already said: Get a comparator. 741 was a remarkable step forward half a century ago, but things have developed better since those days.
answered 2 days ago
user287001user287001
9,6791517
$endgroup$
$begingroup$
Thank you for your response friend, i will update it after changing the opp amp.
$endgroup$
– Nihal
2 days ago
2
$begingroup$
@Nihal Comparators have other precautions. They are high speed circuits like logic parts. You must have acceptably short wires and coupling capacitors between supply voltage inputs. Making the circuit with 0,5 meter long wires onto a breadboard without coupling caps (I have seen those attempts) will be useless.
$endgroup$
– user287001
2 days ago
$begingroup$
Ok friend I will even buy a comparator and I will check with it.
$endgroup$
– Nihal
2 days ago
add a comment |
$begingroup$
Opamps work slowly with low power supply voltages. In addition they are designed to work in linear region. As saturated, like in your application, the response has an unpredictable dead time. before the internal saturation is vanished.
I can only repeat what's already said: Get a comparator. 741 was a remarkable step forward half a century ago, but things have developed better since those days.
answered 2 days ago
user287001user287001
9,6791517
$endgroup$
$begingroup$
Thank you for your response friend, i will update it after changing the opp amp.
$endgroup$
– Nihal
2 days ago
2
$begingroup$
@Nihal Comparators have other precautions. They are high speed circuits like logic parts. You must have acceptably short wires and coupling capacitors between supply voltage inputs. Making the circuit with 0,5 meter long wires onto a breadboard without coupling caps (I have seen those attempts) will be useless.
$endgroup$
– user287001
2 days ago
$begingroup$
Ok friend I will even buy a comparator and I will check with it.
$endgroup$
– Nihal
2 days ago
add a comment |
$begingroup$
Opamps work slowly with low power supply voltages. In addition they are designed to work in linear region. As saturated, like in your application, the response has an unpredictable dead time. before the internal saturation is vanished.
I can only repeat what's already said: Get a comparator. 741 was a remarkable step forward half a century ago, but things have developed better since those days.
answered 2 days ago
user287001user287001
9,6791517
$endgroup$
Opamps work slowly with low power supply voltages. In addition they are designed to work in linear region. As saturated, like in your application, the response has an unpredictable dead time. before the internal saturation is vanished.
I can only repeat what's already said: Get a comparator. 741 was a remarkable step forward half a century ago, but things have developed better since those days.
answered 2 days ago
user287001user287001
9,6791517
answered 2 days ago
user287001user287001
9,6791517
answered 2 days ago
user287001user287001
9,6791517
answered 2 days ago
user287001user287001
9,6791517
9,6791517
$begingroup$
Thank you for your response friend, i will update it after changing the opp amp.
$endgroup$
– Nihal
2 days ago
2
$begingroup$
@Nihal Comparators have other precautions. They are high speed circuits like logic parts. You must have acceptably short wires and coupling capacitors between supply voltage inputs. Making the circuit with 0,5 meter long wires onto a breadboard without coupling caps (I have seen those attempts) will be useless.
$endgroup$
– user287001
2 days ago
$begingroup$
Ok friend I will even buy a comparator and I will check with it.
$endgroup$
– Nihal
2 days ago
add a comment |
$begingroup$
Thank you for your response friend, i will update it after changing the opp amp.
$endgroup$
– Nihal
2 days ago
2
$begingroup$
@Nihal Comparators have other precautions. They are high speed circuits like logic parts. You must have acceptably short wires and coupling capacitors between supply voltage inputs. Making the circuit with 0,5 meter long wires onto a breadboard without coupling caps (I have seen those attempts) will be useless.
$endgroup$
– user287001
2 days ago
$begingroup$
Ok friend I will even buy a comparator and I will check with it.
$endgroup$
– Nihal
2 days ago
$begingroup$
Thank you for your response friend, i will update it after changing the opp amp.
$endgroup$
– Nihal
2 days ago
$begingroup$
Thank you for your response friend, i will update it after changing the opp amp.
$endgroup$
– Nihal
2 days ago
2
2
$begingroup$
@Nihal Comparators have other precautions. They are high speed circuits like logic parts. You must have acceptably short wires and coupling capacitors between supply voltage inputs. Making the circuit with 0,5 meter long wires onto a breadboard without coupling caps (I have seen those attempts) will be useless.
$endgroup$
– user287001
2 days ago
$begingroup$
@Nihal Comparators have other precautions. They are high speed circuits like logic parts. You must have acceptably short wires and coupling capacitors between supply voltage inputs. Making the circuit with 0,5 meter long wires onto a breadboard without coupling caps (I have seen those attempts) will be useless.
$endgroup$
– user287001
2 days ago
$begingroup$
Ok friend I will even buy a comparator and I will check with it.
$endgroup$
– Nihal
2 days ago
$begingroup$
Ok friend I will even buy a comparator and I will check with it.
$endgroup$
– Nihal
2 days ago
add a comment |
$begingroup$
Op-amps are susceptible to latch-up. Recovering from saturation at the rails is not an automatic thing. The ratings you are reading a for the op amp working in a feedback mode, not an open loop mode. You would need to find an op amp designed to minimize latch-up, or better yet, when you need a comparator, buy a comparator.
answered 2 days ago
Scott SeidmanScott Seidman
22.7k43286
$endgroup$
1
$begingroup$
Yes, and/or phase inversion, depending on the op-amp type.
$endgroup$
– Peter Mortensen
2 days ago
add a comment |
$begingroup$
Op-amps are susceptible to latch-up. Recovering from saturation at the rails is not an automatic thing. The ratings you are reading a for the op amp working in a feedback mode, not an open loop mode. You would need to find an op amp designed to minimize latch-up, or better yet, when you need a comparator, buy a comparator.
answered 2 days ago
Scott SeidmanScott Seidman
22.7k43286
$endgroup$
1
$begingroup$
Yes, and/or phase inversion, depending on the op-amp type.
$endgroup$
– Peter Mortensen
2 days ago
add a comment |
$begingroup$
Op-amps are susceptible to latch-up. Recovering from saturation at the rails is not an automatic thing. The ratings you are reading a for the op amp working in a feedback mode, not an open loop mode. You would need to find an op amp designed to minimize latch-up, or better yet, when you need a comparator, buy a comparator.
answered 2 days ago
Scott SeidmanScott Seidman
22.7k43286
$endgroup$
Op-amps are susceptible to latch-up. Recovering from saturation at the rails is not an automatic thing. The ratings you are reading a for the op amp working in a feedback mode, not an open loop mode. You would need to find an op amp designed to minimize latch-up, or better yet, when you need a comparator, buy a comparator.
answered 2 days ago
Scott SeidmanScott Seidman
22.7k43286
answered 2 days ago
Scott SeidmanScott Seidman
22.7k43286
answered 2 days ago
Scott SeidmanScott Seidman
22.7k43286
answered 2 days ago
Scott SeidmanScott Seidman
22.7k43286
22.7k43286
1
$begingroup$
Yes, and/or phase inversion, depending on the op-amp type.
$endgroup$
– Peter Mortensen
2 days ago
add a comment |
1
$begingroup$
Yes, and/or phase inversion, depending on the op-amp type.
$endgroup$
– Peter Mortensen
2 days ago
1
1
$begingroup$
Yes, and/or phase inversion, depending on the op-amp type.
$endgroup$
– Peter Mortensen
2 days ago
$begingroup$
Yes, and/or phase inversion, depending on the op-amp type.
$endgroup$
– Peter Mortensen
2 days ago
add a comment |
$begingroup$
You may try this, if you want a discrete solution
simulate this circuit – Schematic created using CircuitLab
The speed will be limited by Rin (10Kohm) and Miller Effect Cin (100pF?), thus propagation delay will be about 1 uS.
answered 2 days ago
analogsystemsrfanalogsystemsrf
16k2822
$endgroup$
$begingroup$
What is it? A Schmitt trigger?
$endgroup$
– Peter Mortensen
2 days ago
$begingroup$
The differential pair is biased at VDD/2. R8 does provide 1% positive feedback, to reduce the risk of oscillation during the linear region. Notice I included over-voltage protection.
$endgroup$
– analogsystemsrf
2 days ago
add a comment |
$begingroup$
You may try this, if you want a discrete solution
simulate this circuit – Schematic created using CircuitLab
The speed will be limited by Rin (10Kohm) and Miller Effect Cin (100pF?), thus propagation delay will be about 1 uS.
answered 2 days ago
analogsystemsrfanalogsystemsrf
16k2822
$endgroup$
$begingroup$
What is it? A Schmitt trigger?
$endgroup$
– Peter Mortensen
2 days ago
$begingroup$
The differential pair is biased at VDD/2. R8 does provide 1% positive feedback, to reduce the risk of oscillation during the linear region. Notice I included over-voltage protection.
$endgroup$
– analogsystemsrf
2 days ago
add a comment |
$begingroup$
You may try this, if you want a discrete solution
simulate this circuit – Schematic created using CircuitLab
The speed will be limited by Rin (10Kohm) and Miller Effect Cin (100pF?), thus propagation delay will be about 1 uS.
answered 2 days ago
analogsystemsrfanalogsystemsrf
16k2822
$endgroup$
You may try this, if you want a discrete solution
simulate this circuit – Schematic created using CircuitLab
The speed will be limited by Rin (10Kohm) and Miller Effect Cin (100pF?), thus propagation delay will be about 1 uS.
answered 2 days ago
analogsystemsrfanalogsystemsrf
16k2822
edited 50 mins ago
answered 2 days ago
analogsystemsrfanalogsystemsrf
16k2822
answered 2 days ago
analogsystemsrfanalogsystemsrf
16k2822
answered 2 days ago
analogsystemsrfanalogsystemsrf
16k2822
16k2822
$begingroup$
What is it? A Schmitt trigger?
$endgroup$
– Peter Mortensen
2 days ago
$begingroup$
The differential pair is biased at VDD/2. R8 does provide 1% positive feedback, to reduce the risk of oscillation during the linear region. Notice I included over-voltage protection.
$endgroup$
– analogsystemsrf
2 days ago
add a comment |
$begingroup$
What is it? A Schmitt trigger?
$endgroup$
– Peter Mortensen
2 days ago
$begingroup$
The differential pair is biased at VDD/2. R8 does provide 1% positive feedback, to reduce the risk of oscillation during the linear region. Notice I included over-voltage protection.
$endgroup$
– analogsystemsrf
2 days ago
$begingroup$
What is it? A Schmitt trigger?
$endgroup$
– Peter Mortensen
2 days ago
$begingroup$
What is it? A Schmitt trigger?
$endgroup$
– Peter Mortensen
2 days ago
$begingroup$
The differential pair is biased at VDD/2. R8 does provide 1% positive feedback, to reduce the risk of oscillation during the linear region. Notice I included over-voltage protection.
$endgroup$
– analogsystemsrf
2 days ago
$begingroup$
The differential pair is biased at VDD/2. R8 does provide 1% positive feedback, to reduce the risk of oscillation during the linear region. Notice I included over-voltage protection.
$endgroup$
– analogsystemsrf
2 days ago
add a comment |
$begingroup$
Most garden variety op-amps have internal compensation in the form of a chip capacitor.
This makes them very slow, but more stable in analog circuits.
Why not use a cheap comparator like LM393?
edited 2 days ago
Renan
4,32222244
answered 2 days ago
AutisticAutistic
7,50921633
$endgroup$
add a comment |
$begingroup$
Most garden variety op-amps have internal compensation in the form of a chip capacitor.
This makes them very slow, but more stable in analog circuits.
Why not use a cheap comparator like LM393?
edited 2 days ago
Renan
4,32222244
answered 2 days ago
AutisticAutistic
7,50921633
$endgroup$
add a comment |
$begingroup$
Most garden variety op-amps have internal compensation in the form of a chip capacitor.
This makes them very slow, but more stable in analog circuits.
Why not use a cheap comparator like LM393?
edited 2 days ago
Renan
4,32222244
answered 2 days ago
AutisticAutistic
7,50921633
$endgroup$
Most garden variety op-amps have internal compensation in the form of a chip capacitor.
This makes them very slow, but more stable in analog circuits.
Why not use a cheap comparator like LM393?
edited 2 days ago
Renan
4,32222244
answered 2 days ago
AutisticAutistic
7,50921633
edited 2 days ago
Renan
4,32222244
edited 2 days ago
Renan
4,32222244
edited 2 days ago
Renan
4,32222244
4,32222244
answered 2 days ago
AutisticAutistic
7,50921633
answered 2 days ago
AutisticAutistic
7,50921633
answered 2 days ago
AutisticAutistic
7,50921633
7,50921633
add a comment |
add a comment |
Thanks for contributing an answer to Electrical Engineering Stack Exchange!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
Use MathJax to format equations. MathJax reference.
To learn more, see our tips on writing great answers.
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function ()
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2felectronics.stackexchange.com%2fquestions%2f430885%2foperational-amplifier-as-a-comparator-at-high-frequency%23new-answer', 'question_page');
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
$begingroup$
It looks like there's a significant lag/delay in the output's response w.r.t. the input signal (~30µs?). What may be causing this? What's connected to the output? 'Scope probe only?
$endgroup$
– JimmyB
2 days ago
5
$begingroup$
Why you shouldn't use the 741.
$endgroup$
– JRE
2 days ago
$begingroup$
For 5Khz i thought 741 will be ok, for what i calculated .Orelse sure i will change the opp amp which having high slew rate and i will update it.......@JRE
$endgroup$
– Nihal
2 days ago
1
$begingroup$
You're latching up.
$endgroup$
– Scott Seidman
2 days ago
1
$begingroup$
Note that this question is about the theory behind the calculations. Telling OP to change his OP-amp does nothing to answer the question. It just solves the problem without OP knowing why.
$endgroup$
– pipe
2 days ago