If Manufacturer spice model and Datasheet give different values which should I use?Problem with LED Matrix...

How to determine if window is maximised or minimised from bash script

Is there a minimum number of transactions in a block?

What do you call something that goes against the spirit of the law, but is legal when interpreting the law to the letter?

Motorized valve interfering with button?

Download, install and reboot computer at night if needed

Why are 150k or 200k jobs considered good when there are 300k+ births a month?

Is it legal to have the "// (c) 2019 John Smith" header in all files when there are hundreds of contributors?

How do we improve the relationship with a client software team that performs poorly and is becoming less collaborative?

The use of multiple foreign keys on same column in SQL Server

I see my dog run

least quadratic residue under GRH: an EXPLICIT bound

What does "enim et" mean?

Infinite past with a beginning?

Are tax years 2016 & 2017 back taxes deductible for tax year 2018?

What Brexit solution does the DUP want?

Why is the design of haulage companies so “special”?

N.B. ligature in Latex

Accidentally leaked the solution to an assignment, what to do now? (I'm the prof)

Circuitry of TV splitters

Why has Russell's definition of numbers using equivalence classes been finally abandoned? ( If it has actually been abandoned).

Shell script can be run only with sh command

Can I make popcorn with any corn?

Is it possible to do 50 km distance without any previous training?

Example of a relative pronoun



If Manufacturer spice model and Datasheet give different values which should I use?


Problem with LED Matrix TestReference to understand LED data sheet specification, characteristic and way to use themControlling 10 high power LED with a Raspberry Pipspice virtual gnd simulationHow do I model an LED with SPICE WITHOUT access to a Manufacturer's Datasheetsemiconductor resistor vs resistor in SPICE modeling AltiumUsing optocoupler with MOSFET for dimming a LEDHow can I work out which pin is which in SPICE modelAn NPN BJT - from Spice to Ebers-MollModelling heat transfer from Power LED to metal bar






.everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty{ margin-bottom:0;
}







2












$begingroup$


I'm trying to simulate an LED circuit but I am getting a large difference in results from the simulation vs calculations done using the datasheet information. In this case both the spice model and the datasheet info are direct from the manufacturer. Given the large difference in results, I'm wondering which information I should base my design off of.



In this case the datasheet shows a typical Vf of 2.1v, the spice model seems to be using a Vf of 2.134v. I'm wiring 4 of these LEDs in series with a target of 18mA. Assuming a 9v source if I use a 33.3333ohm resistor (or resistor combination) based on the 2.1Vf of the datasheet I get a simulation result of 13.9mA instead of the expected 18mA.



Should I base the resistance off of the datasheet and ignore the simulation in this case, or should I base things more off of the simulation results? I'm asking since if I'm wrong either the LEDs will be too dim, or they will blow out.



I'm attaching the specific simulation and Datasheet in this example here as well. I'm using a SML-P12WTT86R model LED from ROHM Semiconductor.



The datasheet is here.



Here is what I got from the spice simulation using ROHM's spice model.
enter image description here










share|improve this question











$endgroup$












  • $begingroup$
    If a 1% parameter difference makes enough of a difference to care about, your design is probably not robust enough.
    $endgroup$
    – Scott Seidman
    4 hours ago


















2












$begingroup$


I'm trying to simulate an LED circuit but I am getting a large difference in results from the simulation vs calculations done using the datasheet information. In this case both the spice model and the datasheet info are direct from the manufacturer. Given the large difference in results, I'm wondering which information I should base my design off of.



In this case the datasheet shows a typical Vf of 2.1v, the spice model seems to be using a Vf of 2.134v. I'm wiring 4 of these LEDs in series with a target of 18mA. Assuming a 9v source if I use a 33.3333ohm resistor (or resistor combination) based on the 2.1Vf of the datasheet I get a simulation result of 13.9mA instead of the expected 18mA.



Should I base the resistance off of the datasheet and ignore the simulation in this case, or should I base things more off of the simulation results? I'm asking since if I'm wrong either the LEDs will be too dim, or they will blow out.



I'm attaching the specific simulation and Datasheet in this example here as well. I'm using a SML-P12WTT86R model LED from ROHM Semiconductor.



The datasheet is here.



Here is what I got from the spice simulation using ROHM's spice model.
enter image description here










share|improve this question











$endgroup$












  • $begingroup$
    If a 1% parameter difference makes enough of a difference to care about, your design is probably not robust enough.
    $endgroup$
    – Scott Seidman
    4 hours ago














2












2








2





$begingroup$


I'm trying to simulate an LED circuit but I am getting a large difference in results from the simulation vs calculations done using the datasheet information. In this case both the spice model and the datasheet info are direct from the manufacturer. Given the large difference in results, I'm wondering which information I should base my design off of.



In this case the datasheet shows a typical Vf of 2.1v, the spice model seems to be using a Vf of 2.134v. I'm wiring 4 of these LEDs in series with a target of 18mA. Assuming a 9v source if I use a 33.3333ohm resistor (or resistor combination) based on the 2.1Vf of the datasheet I get a simulation result of 13.9mA instead of the expected 18mA.



Should I base the resistance off of the datasheet and ignore the simulation in this case, or should I base things more off of the simulation results? I'm asking since if I'm wrong either the LEDs will be too dim, or they will blow out.



I'm attaching the specific simulation and Datasheet in this example here as well. I'm using a SML-P12WTT86R model LED from ROHM Semiconductor.



The datasheet is here.



Here is what I got from the spice simulation using ROHM's spice model.
enter image description here










share|improve this question











$endgroup$




I'm trying to simulate an LED circuit but I am getting a large difference in results from the simulation vs calculations done using the datasheet information. In this case both the spice model and the datasheet info are direct from the manufacturer. Given the large difference in results, I'm wondering which information I should base my design off of.



In this case the datasheet shows a typical Vf of 2.1v, the spice model seems to be using a Vf of 2.134v. I'm wiring 4 of these LEDs in series with a target of 18mA. Assuming a 9v source if I use a 33.3333ohm resistor (or resistor combination) based on the 2.1Vf of the datasheet I get a simulation result of 13.9mA instead of the expected 18mA.



Should I base the resistance off of the datasheet and ignore the simulation in this case, or should I base things more off of the simulation results? I'm asking since if I'm wrong either the LEDs will be too dim, or they will blow out.



I'm attaching the specific simulation and Datasheet in this example here as well. I'm using a SML-P12WTT86R model LED from ROHM Semiconductor.



The datasheet is here.



Here is what I got from the spice simulation using ROHM's spice model.
enter image description here







led datasheet spice pspice






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited 15 hours ago









jusaca

1,000320




1,000320










asked 15 hours ago









CyFCyF

278




278












  • $begingroup$
    If a 1% parameter difference makes enough of a difference to care about, your design is probably not robust enough.
    $endgroup$
    – Scott Seidman
    4 hours ago


















  • $begingroup$
    If a 1% parameter difference makes enough of a difference to care about, your design is probably not robust enough.
    $endgroup$
    – Scott Seidman
    4 hours ago
















$begingroup$
If a 1% parameter difference makes enough of a difference to care about, your design is probably not robust enough.
$endgroup$
– Scott Seidman
4 hours ago




$begingroup$
If a 1% parameter difference makes enough of a difference to care about, your design is probably not robust enough.
$endgroup$
– Scott Seidman
4 hours ago










2 Answers
2






active

oldest

votes


















4












$begingroup$

Always follow the datasheet. I strongly recommend looking up some of Mike Engelhardt's videos or attend one of his seminars (Arrow sponsors a lot of them). While you're not using LTSpice, Mike has a very deep understanding of Spice simulation, the good, the bad, and the ugly. The reality is most Spice models are made by people that don't really understand them (aka. interns) and can't be trusted a large percent of the time.






share|improve this answer









$endgroup$













  • $begingroup$
    Notice the datasheet value is also only a "typical", not a maximum or minimum.
    $endgroup$
    – The Photon
    15 hours ago










  • $begingroup$
    @ThePhoton Didn't even look at the datasheet, I just know I've seen a lot of crappy Spice models over the years.
    $endgroup$
    – Matt Young
    15 hours ago






  • 1




    $begingroup$
    These days, SPICE models are more likely to be generated by specialized modeling consultants than by interns. The real problem isn't that the person making the model doesn't understand modeling, it's that they can't anticipate every use case that customers will try to apply the device to.
    $endgroup$
    – The Photon
    15 hours ago






  • 1




    $begingroup$
    It may also be that the samples of the part that were used to extract the SPICE model actually had a $V_f$ of 2.134 V at 18 mA, but on the datasheet they rounded this to 2.1 V because they know it will vary by more than a few 10's of mV due to process.
    $endgroup$
    – The Photon
    9 hours ago








  • 1




    $begingroup$
    @MattYoung. I had a chance to briefly speak with Mike Engelhardt. His main gripe with most Spice models is that they follow a Boyle model (analog.com/media/en/technical-documentation/application-notes/…). The problem with this model is that it typically produces incorrect power draw numbers and hides higher order effects that the designer does not show. Mike told me for LT they focus on more detailed simulation that takes advantage of stronger modern processors and should provide better resutls.
    $endgroup$
    – Gonzik007
    9 hours ago





















10












$begingroup$


In this case the datasheet shows a typical Vf of 2.1v, the spice model seems to be using a Vf of 2.134v.




If your circuit works for $V_f$ of 2.1 V, but fails for 2.134 V, then you need to get a new circuit.



The forward voltage will vary due to manufacturing variations and junction temperature. And the variation will be more than 35 mV over realistic operating conditions.



Also, keep in mind that the datasheet value is for an ambient temperature of 25 C, while SPICE is probably (unless you've added an option to specify otherwise) simulating a junction temperature of 25 C. That means the datasheet value reflects a higher junction temperature than the SPICE model. And forward voltage does typically drop with increasing temperature so it's conceivable both models are correct.




Assuming a 9v source if I use a 33.3333ohm resistor (or resistor combination) based on the 2.1Vf of the datasheet I get a simulation result of 13.9mA instead of the expected 18mA. ... I'm asking since if I'm wrong either the LEDs will be too dim, or they will blow out.




If this application requires the brightness to be controlled so carefully that the difference between 13.9 and 18 mA makes a difference, you should use a constant current LED driver instead of a simple resistive current limiter.



But in most applications, users won't notice the difference in brightness due to this kind of current change. So you just live with some brightness variability to save cost. Modern LEDs are visibly lit even with 1 mA forward current so whether at 13.9 or 18 mA they will be quite bright.



You could also reduce the variability by designing your resistive limiting circuit with more voltage overhead. Either use a higher voltage source (12 V maybe) and a larger resistor, or place 2 strings of 2 LEDs in parallel, so you have roughly 5 V overhead instead of just 1. The trade-off here is of course more power wasted in the resistors.






share|improve this answer











$endgroup$













  • $begingroup$
    Well when using small # of LEDs in the series the closer the results get to what I’d have expected from the data sheet. Thanks for all of the input. Here and below.
    $endgroup$
    – CyF
    8 hours ago












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
});


}
});














draft saved

draft discarded


















StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2felectronics.stackexchange.com%2fquestions%2f431255%2fif-manufacturer-spice-model-and-datasheet-give-different-values-which-should-i-u%23new-answer', 'question_page');
}
);

Post as a guest















Required, but never shown

























2 Answers
2






active

oldest

votes








2 Answers
2






active

oldest

votes









active

oldest

votes






active

oldest

votes









4












$begingroup$

Always follow the datasheet. I strongly recommend looking up some of Mike Engelhardt's videos or attend one of his seminars (Arrow sponsors a lot of them). While you're not using LTSpice, Mike has a very deep understanding of Spice simulation, the good, the bad, and the ugly. The reality is most Spice models are made by people that don't really understand them (aka. interns) and can't be trusted a large percent of the time.






share|improve this answer









$endgroup$













  • $begingroup$
    Notice the datasheet value is also only a "typical", not a maximum or minimum.
    $endgroup$
    – The Photon
    15 hours ago










  • $begingroup$
    @ThePhoton Didn't even look at the datasheet, I just know I've seen a lot of crappy Spice models over the years.
    $endgroup$
    – Matt Young
    15 hours ago






  • 1




    $begingroup$
    These days, SPICE models are more likely to be generated by specialized modeling consultants than by interns. The real problem isn't that the person making the model doesn't understand modeling, it's that they can't anticipate every use case that customers will try to apply the device to.
    $endgroup$
    – The Photon
    15 hours ago






  • 1




    $begingroup$
    It may also be that the samples of the part that were used to extract the SPICE model actually had a $V_f$ of 2.134 V at 18 mA, but on the datasheet they rounded this to 2.1 V because they know it will vary by more than a few 10's of mV due to process.
    $endgroup$
    – The Photon
    9 hours ago








  • 1




    $begingroup$
    @MattYoung. I had a chance to briefly speak with Mike Engelhardt. His main gripe with most Spice models is that they follow a Boyle model (analog.com/media/en/technical-documentation/application-notes/…). The problem with this model is that it typically produces incorrect power draw numbers and hides higher order effects that the designer does not show. Mike told me for LT they focus on more detailed simulation that takes advantage of stronger modern processors and should provide better resutls.
    $endgroup$
    – Gonzik007
    9 hours ago


















4












$begingroup$

Always follow the datasheet. I strongly recommend looking up some of Mike Engelhardt's videos or attend one of his seminars (Arrow sponsors a lot of them). While you're not using LTSpice, Mike has a very deep understanding of Spice simulation, the good, the bad, and the ugly. The reality is most Spice models are made by people that don't really understand them (aka. interns) and can't be trusted a large percent of the time.






share|improve this answer









$endgroup$













  • $begingroup$
    Notice the datasheet value is also only a "typical", not a maximum or minimum.
    $endgroup$
    – The Photon
    15 hours ago










  • $begingroup$
    @ThePhoton Didn't even look at the datasheet, I just know I've seen a lot of crappy Spice models over the years.
    $endgroup$
    – Matt Young
    15 hours ago






  • 1




    $begingroup$
    These days, SPICE models are more likely to be generated by specialized modeling consultants than by interns. The real problem isn't that the person making the model doesn't understand modeling, it's that they can't anticipate every use case that customers will try to apply the device to.
    $endgroup$
    – The Photon
    15 hours ago






  • 1




    $begingroup$
    It may also be that the samples of the part that were used to extract the SPICE model actually had a $V_f$ of 2.134 V at 18 mA, but on the datasheet they rounded this to 2.1 V because they know it will vary by more than a few 10's of mV due to process.
    $endgroup$
    – The Photon
    9 hours ago








  • 1




    $begingroup$
    @MattYoung. I had a chance to briefly speak with Mike Engelhardt. His main gripe with most Spice models is that they follow a Boyle model (analog.com/media/en/technical-documentation/application-notes/…). The problem with this model is that it typically produces incorrect power draw numbers and hides higher order effects that the designer does not show. Mike told me for LT they focus on more detailed simulation that takes advantage of stronger modern processors and should provide better resutls.
    $endgroup$
    – Gonzik007
    9 hours ago
















4












4








4





$begingroup$

Always follow the datasheet. I strongly recommend looking up some of Mike Engelhardt's videos or attend one of his seminars (Arrow sponsors a lot of them). While you're not using LTSpice, Mike has a very deep understanding of Spice simulation, the good, the bad, and the ugly. The reality is most Spice models are made by people that don't really understand them (aka. interns) and can't be trusted a large percent of the time.






share|improve this answer









$endgroup$



Always follow the datasheet. I strongly recommend looking up some of Mike Engelhardt's videos or attend one of his seminars (Arrow sponsors a lot of them). While you're not using LTSpice, Mike has a very deep understanding of Spice simulation, the good, the bad, and the ugly. The reality is most Spice models are made by people that don't really understand them (aka. interns) and can't be trusted a large percent of the time.







share|improve this answer












share|improve this answer



share|improve this answer










answered 15 hours ago









Matt YoungMatt Young

12.4k42560




12.4k42560












  • $begingroup$
    Notice the datasheet value is also only a "typical", not a maximum or minimum.
    $endgroup$
    – The Photon
    15 hours ago










  • $begingroup$
    @ThePhoton Didn't even look at the datasheet, I just know I've seen a lot of crappy Spice models over the years.
    $endgroup$
    – Matt Young
    15 hours ago






  • 1




    $begingroup$
    These days, SPICE models are more likely to be generated by specialized modeling consultants than by interns. The real problem isn't that the person making the model doesn't understand modeling, it's that they can't anticipate every use case that customers will try to apply the device to.
    $endgroup$
    – The Photon
    15 hours ago






  • 1




    $begingroup$
    It may also be that the samples of the part that were used to extract the SPICE model actually had a $V_f$ of 2.134 V at 18 mA, but on the datasheet they rounded this to 2.1 V because they know it will vary by more than a few 10's of mV due to process.
    $endgroup$
    – The Photon
    9 hours ago








  • 1




    $begingroup$
    @MattYoung. I had a chance to briefly speak with Mike Engelhardt. His main gripe with most Spice models is that they follow a Boyle model (analog.com/media/en/technical-documentation/application-notes/…). The problem with this model is that it typically produces incorrect power draw numbers and hides higher order effects that the designer does not show. Mike told me for LT they focus on more detailed simulation that takes advantage of stronger modern processors and should provide better resutls.
    $endgroup$
    – Gonzik007
    9 hours ago




















  • $begingroup$
    Notice the datasheet value is also only a "typical", not a maximum or minimum.
    $endgroup$
    – The Photon
    15 hours ago










  • $begingroup$
    @ThePhoton Didn't even look at the datasheet, I just know I've seen a lot of crappy Spice models over the years.
    $endgroup$
    – Matt Young
    15 hours ago






  • 1




    $begingroup$
    These days, SPICE models are more likely to be generated by specialized modeling consultants than by interns. The real problem isn't that the person making the model doesn't understand modeling, it's that they can't anticipate every use case that customers will try to apply the device to.
    $endgroup$
    – The Photon
    15 hours ago






  • 1




    $begingroup$
    It may also be that the samples of the part that were used to extract the SPICE model actually had a $V_f$ of 2.134 V at 18 mA, but on the datasheet they rounded this to 2.1 V because they know it will vary by more than a few 10's of mV due to process.
    $endgroup$
    – The Photon
    9 hours ago








  • 1




    $begingroup$
    @MattYoung. I had a chance to briefly speak with Mike Engelhardt. His main gripe with most Spice models is that they follow a Boyle model (analog.com/media/en/technical-documentation/application-notes/…). The problem with this model is that it typically produces incorrect power draw numbers and hides higher order effects that the designer does not show. Mike told me for LT they focus on more detailed simulation that takes advantage of stronger modern processors and should provide better resutls.
    $endgroup$
    – Gonzik007
    9 hours ago


















$begingroup$
Notice the datasheet value is also only a "typical", not a maximum or minimum.
$endgroup$
– The Photon
15 hours ago




$begingroup$
Notice the datasheet value is also only a "typical", not a maximum or minimum.
$endgroup$
– The Photon
15 hours ago












$begingroup$
@ThePhoton Didn't even look at the datasheet, I just know I've seen a lot of crappy Spice models over the years.
$endgroup$
– Matt Young
15 hours ago




$begingroup$
@ThePhoton Didn't even look at the datasheet, I just know I've seen a lot of crappy Spice models over the years.
$endgroup$
– Matt Young
15 hours ago




1




1




$begingroup$
These days, SPICE models are more likely to be generated by specialized modeling consultants than by interns. The real problem isn't that the person making the model doesn't understand modeling, it's that they can't anticipate every use case that customers will try to apply the device to.
$endgroup$
– The Photon
15 hours ago




$begingroup$
These days, SPICE models are more likely to be generated by specialized modeling consultants than by interns. The real problem isn't that the person making the model doesn't understand modeling, it's that they can't anticipate every use case that customers will try to apply the device to.
$endgroup$
– The Photon
15 hours ago




1




1




$begingroup$
It may also be that the samples of the part that were used to extract the SPICE model actually had a $V_f$ of 2.134 V at 18 mA, but on the datasheet they rounded this to 2.1 V because they know it will vary by more than a few 10's of mV due to process.
$endgroup$
– The Photon
9 hours ago






$begingroup$
It may also be that the samples of the part that were used to extract the SPICE model actually had a $V_f$ of 2.134 V at 18 mA, but on the datasheet they rounded this to 2.1 V because they know it will vary by more than a few 10's of mV due to process.
$endgroup$
– The Photon
9 hours ago






1




1




$begingroup$
@MattYoung. I had a chance to briefly speak with Mike Engelhardt. His main gripe with most Spice models is that they follow a Boyle model (analog.com/media/en/technical-documentation/application-notes/…). The problem with this model is that it typically produces incorrect power draw numbers and hides higher order effects that the designer does not show. Mike told me for LT they focus on more detailed simulation that takes advantage of stronger modern processors and should provide better resutls.
$endgroup$
– Gonzik007
9 hours ago






$begingroup$
@MattYoung. I had a chance to briefly speak with Mike Engelhardt. His main gripe with most Spice models is that they follow a Boyle model (analog.com/media/en/technical-documentation/application-notes/…). The problem with this model is that it typically produces incorrect power draw numbers and hides higher order effects that the designer does not show. Mike told me for LT they focus on more detailed simulation that takes advantage of stronger modern processors and should provide better resutls.
$endgroup$
– Gonzik007
9 hours ago















10












$begingroup$


In this case the datasheet shows a typical Vf of 2.1v, the spice model seems to be using a Vf of 2.134v.




If your circuit works for $V_f$ of 2.1 V, but fails for 2.134 V, then you need to get a new circuit.



The forward voltage will vary due to manufacturing variations and junction temperature. And the variation will be more than 35 mV over realistic operating conditions.



Also, keep in mind that the datasheet value is for an ambient temperature of 25 C, while SPICE is probably (unless you've added an option to specify otherwise) simulating a junction temperature of 25 C. That means the datasheet value reflects a higher junction temperature than the SPICE model. And forward voltage does typically drop with increasing temperature so it's conceivable both models are correct.




Assuming a 9v source if I use a 33.3333ohm resistor (or resistor combination) based on the 2.1Vf of the datasheet I get a simulation result of 13.9mA instead of the expected 18mA. ... I'm asking since if I'm wrong either the LEDs will be too dim, or they will blow out.




If this application requires the brightness to be controlled so carefully that the difference between 13.9 and 18 mA makes a difference, you should use a constant current LED driver instead of a simple resistive current limiter.



But in most applications, users won't notice the difference in brightness due to this kind of current change. So you just live with some brightness variability to save cost. Modern LEDs are visibly lit even with 1 mA forward current so whether at 13.9 or 18 mA they will be quite bright.



You could also reduce the variability by designing your resistive limiting circuit with more voltage overhead. Either use a higher voltage source (12 V maybe) and a larger resistor, or place 2 strings of 2 LEDs in parallel, so you have roughly 5 V overhead instead of just 1. The trade-off here is of course more power wasted in the resistors.






share|improve this answer











$endgroup$













  • $begingroup$
    Well when using small # of LEDs in the series the closer the results get to what I’d have expected from the data sheet. Thanks for all of the input. Here and below.
    $endgroup$
    – CyF
    8 hours ago
















10












$begingroup$


In this case the datasheet shows a typical Vf of 2.1v, the spice model seems to be using a Vf of 2.134v.




If your circuit works for $V_f$ of 2.1 V, but fails for 2.134 V, then you need to get a new circuit.



The forward voltage will vary due to manufacturing variations and junction temperature. And the variation will be more than 35 mV over realistic operating conditions.



Also, keep in mind that the datasheet value is for an ambient temperature of 25 C, while SPICE is probably (unless you've added an option to specify otherwise) simulating a junction temperature of 25 C. That means the datasheet value reflects a higher junction temperature than the SPICE model. And forward voltage does typically drop with increasing temperature so it's conceivable both models are correct.




Assuming a 9v source if I use a 33.3333ohm resistor (or resistor combination) based on the 2.1Vf of the datasheet I get a simulation result of 13.9mA instead of the expected 18mA. ... I'm asking since if I'm wrong either the LEDs will be too dim, or they will blow out.




If this application requires the brightness to be controlled so carefully that the difference between 13.9 and 18 mA makes a difference, you should use a constant current LED driver instead of a simple resistive current limiter.



But in most applications, users won't notice the difference in brightness due to this kind of current change. So you just live with some brightness variability to save cost. Modern LEDs are visibly lit even with 1 mA forward current so whether at 13.9 or 18 mA they will be quite bright.



You could also reduce the variability by designing your resistive limiting circuit with more voltage overhead. Either use a higher voltage source (12 V maybe) and a larger resistor, or place 2 strings of 2 LEDs in parallel, so you have roughly 5 V overhead instead of just 1. The trade-off here is of course more power wasted in the resistors.






share|improve this answer











$endgroup$













  • $begingroup$
    Well when using small # of LEDs in the series the closer the results get to what I’d have expected from the data sheet. Thanks for all of the input. Here and below.
    $endgroup$
    – CyF
    8 hours ago














10












10








10





$begingroup$


In this case the datasheet shows a typical Vf of 2.1v, the spice model seems to be using a Vf of 2.134v.




If your circuit works for $V_f$ of 2.1 V, but fails for 2.134 V, then you need to get a new circuit.



The forward voltage will vary due to manufacturing variations and junction temperature. And the variation will be more than 35 mV over realistic operating conditions.



Also, keep in mind that the datasheet value is for an ambient temperature of 25 C, while SPICE is probably (unless you've added an option to specify otherwise) simulating a junction temperature of 25 C. That means the datasheet value reflects a higher junction temperature than the SPICE model. And forward voltage does typically drop with increasing temperature so it's conceivable both models are correct.




Assuming a 9v source if I use a 33.3333ohm resistor (or resistor combination) based on the 2.1Vf of the datasheet I get a simulation result of 13.9mA instead of the expected 18mA. ... I'm asking since if I'm wrong either the LEDs will be too dim, or they will blow out.




If this application requires the brightness to be controlled so carefully that the difference between 13.9 and 18 mA makes a difference, you should use a constant current LED driver instead of a simple resistive current limiter.



But in most applications, users won't notice the difference in brightness due to this kind of current change. So you just live with some brightness variability to save cost. Modern LEDs are visibly lit even with 1 mA forward current so whether at 13.9 or 18 mA they will be quite bright.



You could also reduce the variability by designing your resistive limiting circuit with more voltage overhead. Either use a higher voltage source (12 V maybe) and a larger resistor, or place 2 strings of 2 LEDs in parallel, so you have roughly 5 V overhead instead of just 1. The trade-off here is of course more power wasted in the resistors.






share|improve this answer











$endgroup$




In this case the datasheet shows a typical Vf of 2.1v, the spice model seems to be using a Vf of 2.134v.




If your circuit works for $V_f$ of 2.1 V, but fails for 2.134 V, then you need to get a new circuit.



The forward voltage will vary due to manufacturing variations and junction temperature. And the variation will be more than 35 mV over realistic operating conditions.



Also, keep in mind that the datasheet value is for an ambient temperature of 25 C, while SPICE is probably (unless you've added an option to specify otherwise) simulating a junction temperature of 25 C. That means the datasheet value reflects a higher junction temperature than the SPICE model. And forward voltage does typically drop with increasing temperature so it's conceivable both models are correct.




Assuming a 9v source if I use a 33.3333ohm resistor (or resistor combination) based on the 2.1Vf of the datasheet I get a simulation result of 13.9mA instead of the expected 18mA. ... I'm asking since if I'm wrong either the LEDs will be too dim, or they will blow out.




If this application requires the brightness to be controlled so carefully that the difference between 13.9 and 18 mA makes a difference, you should use a constant current LED driver instead of a simple resistive current limiter.



But in most applications, users won't notice the difference in brightness due to this kind of current change. So you just live with some brightness variability to save cost. Modern LEDs are visibly lit even with 1 mA forward current so whether at 13.9 or 18 mA they will be quite bright.



You could also reduce the variability by designing your resistive limiting circuit with more voltage overhead. Either use a higher voltage source (12 V maybe) and a larger resistor, or place 2 strings of 2 LEDs in parallel, so you have roughly 5 V overhead instead of just 1. The trade-off here is of course more power wasted in the resistors.







share|improve this answer














share|improve this answer



share|improve this answer








edited 9 hours ago

























answered 15 hours ago









The PhotonThe Photon

87.1k398203




87.1k398203












  • $begingroup$
    Well when using small # of LEDs in the series the closer the results get to what I’d have expected from the data sheet. Thanks for all of the input. Here and below.
    $endgroup$
    – CyF
    8 hours ago


















  • $begingroup$
    Well when using small # of LEDs in the series the closer the results get to what I’d have expected from the data sheet. Thanks for all of the input. Here and below.
    $endgroup$
    – CyF
    8 hours ago
















$begingroup$
Well when using small # of LEDs in the series the closer the results get to what I’d have expected from the data sheet. Thanks for all of the input. Here and below.
$endgroup$
– CyF
8 hours ago




$begingroup$
Well when using small # of LEDs in the series the closer the results get to what I’d have expected from the data sheet. Thanks for all of the input. Here and below.
$endgroup$
– CyF
8 hours ago


















draft saved

draft discarded




















































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.




draft saved


draft discarded














StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2felectronics.stackexchange.com%2fquestions%2f431255%2fif-manufacturer-spice-model-and-datasheet-give-different-values-which-should-i-u%23new-answer', 'question_page');
}
);

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







Popular posts from this blog

El tren de la libertad Índice Antecedentes "Porque yo decido" Desarrollo de la...

Puerta de Hutt Referencias Enlaces externos Menú de navegación15°58′00″S 5°42′00″O /...

Castillo d'Acher Características Menú de navegación