Can I use a single resistor for multiple LED with different +ve sources?












2












$begingroup$


In the photo below I would like to use a single resistor after the LEDs, instead of having individual resistors before the LEDs. Is this problematic? Will it work?



enter image description here






arduino microcontroller led







share|improve this question









$endgroup$








  • 2




    $begingroup$
    No, there are tolerances inbetween one LED and another. The LED with the lowest Vf will carry a lot more current then the others.
    $endgroup$
    – Unimportant
    5 hours ago






  • 1




    $begingroup$
    Looks like Diode OR logic ;) but problematic due to sharing current and voltage drop.
    $endgroup$
    – Sunnyskyguy EE75
    4 hours ago
















2












$begingroup$


In the photo below I would like to use a single resistor after the LEDs, instead of having individual resistors before the LEDs. Is this problematic? Will it work?



enter image description here






arduino microcontroller led







share|improve this question









$endgroup$








  • 2




    $begingroup$
    No, there are tolerances inbetween one LED and another. The LED with the lowest Vf will carry a lot more current then the others.
    $endgroup$
    – Unimportant
    5 hours ago






  • 1




    $begingroup$
    Looks like Diode OR logic ;) but problematic due to sharing current and voltage drop.
    $endgroup$
    – Sunnyskyguy EE75
    4 hours ago














2












2








2





$begingroup$


In the photo below I would like to use a single resistor after the LEDs, instead of having individual resistors before the LEDs. Is this problematic? Will it work?



enter image description here






arduino microcontroller led







share|improve this question









$endgroup$




In the photo below I would like to use a single resistor after the LEDs, instead of having individual resistors before the LEDs. Is this problematic? Will it work?



enter image description here






arduino microcontroller led




arduino microcontroller led






share|improve this question













share|improve this question











share|improve this question




share|improve this question










asked 5 hours ago









DonPDonP

307




307








  • 2




    $begingroup$
    No, there are tolerances inbetween one LED and another. The LED with the lowest Vf will carry a lot more current then the others.
    $endgroup$
    – Unimportant
    5 hours ago






  • 1




    $begingroup$
    Looks like Diode OR logic ;) but problematic due to sharing current and voltage drop.
    $endgroup$
    – Sunnyskyguy EE75
    4 hours ago














  • 2




    $begingroup$
    No, there are tolerances inbetween one LED and another. The LED with the lowest Vf will carry a lot more current then the others.
    $endgroup$
    – Unimportant
    5 hours ago






  • 1




    $begingroup$
    Looks like Diode OR logic ;) but problematic due to sharing current and voltage drop.
    $endgroup$
    – Sunnyskyguy EE75
    4 hours ago








2




2




$begingroup$
No, there are tolerances inbetween one LED and another. The LED with the lowest Vf will carry a lot more current then the others.
$endgroup$
– Unimportant
5 hours ago




$begingroup$
No, there are tolerances inbetween one LED and another. The LED with the lowest Vf will carry a lot more current then the others.
$endgroup$
– Unimportant
5 hours ago




1




1




$begingroup$
Looks like Diode OR logic ;) but problematic due to sharing current and voltage drop.
$endgroup$
– Sunnyskyguy EE75
4 hours ago




$begingroup$
Looks like Diode OR logic ;) but problematic due to sharing current and voltage drop.
$endgroup$
– Sunnyskyguy EE75
4 hours ago










2 Answers
2






active

oldest

votes


















7












$begingroup$

You can do that safely if:




  • Only one LED is on at a time.

  • The voltage of the circuit is less than the maximum reverse voltage of the LEDs. This often isn't specified by 5 V is generally quite safe.


Otherwise switching two or more on at a time connects them in parallel. In this situation the one with the lowest forward voltage will pass the most current. If they are different colour LEDs then the one with the lowest forward voltage, Vf, will be quite bright and the others relatively dim.



enter image description here



Figure 1. Variations in Vf with different colours of LEDs. Source: LED I-V curves.



enter image description here



Figure 2. Variations in Vf for the same type of LED due to variations in manufacture. Source: Variations in Vf and binning.




As you reminded me in the comments, I forgot to cover the current sharing aspect. The voltage at the top of R1 will be reasonably constant (because the voltage drop across the LEDs would be reasonably similar) so the current through R1 will be constant if one or more LEDs is on. That means that the current will be shared between the LEDs - fairly evenly if they're all the same colour but not so evenly if not.






share|improve this answer











$endgroup$













  • $begingroup$
    So if switching 2 on at once is connecting them in parallel, this would mean the current drop would roughly double? And the resistor if limiting to 15ma would be shared between the 2 LED and would only see 7.5ma (roughly)?
    $endgroup$
    – DonP
    4 hours ago










  • $begingroup$
    Correct, and I completely forgot to cover that in the answer. I'll add it in.
    $endgroup$
    – Transistor
    4 hours ago












  • $begingroup$
    OK. Will mark as answer. THanks for the detailed response.
    $endgroup$
    – DonP
    4 hours ago



















0












$begingroup$

It's problematic because nothing is ever identical so the LED with the lowest voltage drop will cause all the current to flow through it while the other two LEDs never turn on because the voltage drop across them isn't high enough.






share|improve this answer









$endgroup$









  • 1




    $begingroup$
    even though they have different +ve signal source?
    $endgroup$
    – DonP
    4 hours ago










  • $begingroup$
    As the others have pointed out above, it's okay if you only ever turn on one at a time. You'll run into trouble if you try to turn on more than one at a time.
    $endgroup$
    – Toor
    4 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%2f424033%2fcan-i-use-a-single-resistor-for-multiple-led-with-different-ve-sources%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









7












$begingroup$

You can do that safely if:




  • Only one LED is on at a time.

  • The voltage of the circuit is less than the maximum reverse voltage of the LEDs. This often isn't specified by 5 V is generally quite safe.


Otherwise switching two or more on at a time connects them in parallel. In this situation the one with the lowest forward voltage will pass the most current. If they are different colour LEDs then the one with the lowest forward voltage, Vf, will be quite bright and the others relatively dim.



enter image description here



Figure 1. Variations in Vf with different colours of LEDs. Source: LED I-V curves.



enter image description here



Figure 2. Variations in Vf for the same type of LED due to variations in manufacture. Source: Variations in Vf and binning.




As you reminded me in the comments, I forgot to cover the current sharing aspect. The voltage at the top of R1 will be reasonably constant (because the voltage drop across the LEDs would be reasonably similar) so the current through R1 will be constant if one or more LEDs is on. That means that the current will be shared between the LEDs - fairly evenly if they're all the same colour but not so evenly if not.






share|improve this answer











$endgroup$













  • $begingroup$
    So if switching 2 on at once is connecting them in parallel, this would mean the current drop would roughly double? And the resistor if limiting to 15ma would be shared between the 2 LED and would only see 7.5ma (roughly)?
    $endgroup$
    – DonP
    4 hours ago










  • $begingroup$
    Correct, and I completely forgot to cover that in the answer. I'll add it in.
    $endgroup$
    – Transistor
    4 hours ago












  • $begingroup$
    OK. Will mark as answer. THanks for the detailed response.
    $endgroup$
    – DonP
    4 hours ago
















7












$begingroup$

You can do that safely if:




  • Only one LED is on at a time.

  • The voltage of the circuit is less than the maximum reverse voltage of the LEDs. This often isn't specified by 5 V is generally quite safe.


Otherwise switching two or more on at a time connects them in parallel. In this situation the one with the lowest forward voltage will pass the most current. If they are different colour LEDs then the one with the lowest forward voltage, Vf, will be quite bright and the others relatively dim.



enter image description here



Figure 1. Variations in Vf with different colours of LEDs. Source: LED I-V curves.



enter image description here



Figure 2. Variations in Vf for the same type of LED due to variations in manufacture. Source: Variations in Vf and binning.




As you reminded me in the comments, I forgot to cover the current sharing aspect. The voltage at the top of R1 will be reasonably constant (because the voltage drop across the LEDs would be reasonably similar) so the current through R1 will be constant if one or more LEDs is on. That means that the current will be shared between the LEDs - fairly evenly if they're all the same colour but not so evenly if not.






share|improve this answer











$endgroup$













  • $begingroup$
    So if switching 2 on at once is connecting them in parallel, this would mean the current drop would roughly double? And the resistor if limiting to 15ma would be shared between the 2 LED and would only see 7.5ma (roughly)?
    $endgroup$
    – DonP
    4 hours ago










  • $begingroup$
    Correct, and I completely forgot to cover that in the answer. I'll add it in.
    $endgroup$
    – Transistor
    4 hours ago












  • $begingroup$
    OK. Will mark as answer. THanks for the detailed response.
    $endgroup$
    – DonP
    4 hours ago














7












7








7





$begingroup$

You can do that safely if:




  • Only one LED is on at a time.

  • The voltage of the circuit is less than the maximum reverse voltage of the LEDs. This often isn't specified by 5 V is generally quite safe.


Otherwise switching two or more on at a time connects them in parallel. In this situation the one with the lowest forward voltage will pass the most current. If they are different colour LEDs then the one with the lowest forward voltage, Vf, will be quite bright and the others relatively dim.



enter image description here



Figure 1. Variations in Vf with different colours of LEDs. Source: LED I-V curves.



enter image description here



Figure 2. Variations in Vf for the same type of LED due to variations in manufacture. Source: Variations in Vf and binning.




As you reminded me in the comments, I forgot to cover the current sharing aspect. The voltage at the top of R1 will be reasonably constant (because the voltage drop across the LEDs would be reasonably similar) so the current through R1 will be constant if one or more LEDs is on. That means that the current will be shared between the LEDs - fairly evenly if they're all the same colour but not so evenly if not.






share|improve this answer











$endgroup$



You can do that safely if:




  • Only one LED is on at a time.

  • The voltage of the circuit is less than the maximum reverse voltage of the LEDs. This often isn't specified by 5 V is generally quite safe.


Otherwise switching two or more on at a time connects them in parallel. In this situation the one with the lowest forward voltage will pass the most current. If they are different colour LEDs then the one with the lowest forward voltage, Vf, will be quite bright and the others relatively dim.



enter image description here



Figure 1. Variations in Vf with different colours of LEDs. Source: LED I-V curves.



enter image description here



Figure 2. Variations in Vf for the same type of LED due to variations in manufacture. Source: Variations in Vf and binning.




As you reminded me in the comments, I forgot to cover the current sharing aspect. The voltage at the top of R1 will be reasonably constant (because the voltage drop across the LEDs would be reasonably similar) so the current through R1 will be constant if one or more LEDs is on. That means that the current will be shared between the LEDs - fairly evenly if they're all the same colour but not so evenly if not.







share|improve this answer














share|improve this answer



share|improve this answer








edited 4 hours ago

























answered 5 hours ago









TransistorTransistor

85.2k784181




85.2k784181












  • $begingroup$
    So if switching 2 on at once is connecting them in parallel, this would mean the current drop would roughly double? And the resistor if limiting to 15ma would be shared between the 2 LED and would only see 7.5ma (roughly)?
    $endgroup$
    – DonP
    4 hours ago










  • $begingroup$
    Correct, and I completely forgot to cover that in the answer. I'll add it in.
    $endgroup$
    – Transistor
    4 hours ago












  • $begingroup$
    OK. Will mark as answer. THanks for the detailed response.
    $endgroup$
    – DonP
    4 hours ago


















  • $begingroup$
    So if switching 2 on at once is connecting them in parallel, this would mean the current drop would roughly double? And the resistor if limiting to 15ma would be shared between the 2 LED and would only see 7.5ma (roughly)?
    $endgroup$
    – DonP
    4 hours ago










  • $begingroup$
    Correct, and I completely forgot to cover that in the answer. I'll add it in.
    $endgroup$
    – Transistor
    4 hours ago












  • $begingroup$
    OK. Will mark as answer. THanks for the detailed response.
    $endgroup$
    – DonP
    4 hours ago
















$begingroup$
So if switching 2 on at once is connecting them in parallel, this would mean the current drop would roughly double? And the resistor if limiting to 15ma would be shared between the 2 LED and would only see 7.5ma (roughly)?
$endgroup$
– DonP
4 hours ago




$begingroup$
So if switching 2 on at once is connecting them in parallel, this would mean the current drop would roughly double? And the resistor if limiting to 15ma would be shared between the 2 LED and would only see 7.5ma (roughly)?
$endgroup$
– DonP
4 hours ago












$begingroup$
Correct, and I completely forgot to cover that in the answer. I'll add it in.
$endgroup$
– Transistor
4 hours ago






$begingroup$
Correct, and I completely forgot to cover that in the answer. I'll add it in.
$endgroup$
– Transistor
4 hours ago














$begingroup$
OK. Will mark as answer. THanks for the detailed response.
$endgroup$
– DonP
4 hours ago




$begingroup$
OK. Will mark as answer. THanks for the detailed response.
$endgroup$
– DonP
4 hours ago













0












$begingroup$

It's problematic because nothing is ever identical so the LED with the lowest voltage drop will cause all the current to flow through it while the other two LEDs never turn on because the voltage drop across them isn't high enough.






share|improve this answer









$endgroup$









  • 1




    $begingroup$
    even though they have different +ve signal source?
    $endgroup$
    – DonP
    4 hours ago










  • $begingroup$
    As the others have pointed out above, it's okay if you only ever turn on one at a time. You'll run into trouble if you try to turn on more than one at a time.
    $endgroup$
    – Toor
    4 hours ago


















0












$begingroup$

It's problematic because nothing is ever identical so the LED with the lowest voltage drop will cause all the current to flow through it while the other two LEDs never turn on because the voltage drop across them isn't high enough.






share|improve this answer









$endgroup$









  • 1




    $begingroup$
    even though they have different +ve signal source?
    $endgroup$
    – DonP
    4 hours ago










  • $begingroup$
    As the others have pointed out above, it's okay if you only ever turn on one at a time. You'll run into trouble if you try to turn on more than one at a time.
    $endgroup$
    – Toor
    4 hours ago
















0












0








0





$begingroup$

It's problematic because nothing is ever identical so the LED with the lowest voltage drop will cause all the current to flow through it while the other two LEDs never turn on because the voltage drop across them isn't high enough.






share|improve this answer









$endgroup$



It's problematic because nothing is ever identical so the LED with the lowest voltage drop will cause all the current to flow through it while the other two LEDs never turn on because the voltage drop across them isn't high enough.







share|improve this answer












share|improve this answer



share|improve this answer










answered 5 hours ago









ToorToor

72219




72219








  • 1




    $begingroup$
    even though they have different +ve signal source?
    $endgroup$
    – DonP
    4 hours ago










  • $begingroup$
    As the others have pointed out above, it's okay if you only ever turn on one at a time. You'll run into trouble if you try to turn on more than one at a time.
    $endgroup$
    – Toor
    4 hours ago
















  • 1




    $begingroup$
    even though they have different +ve signal source?
    $endgroup$
    – DonP
    4 hours ago










  • $begingroup$
    As the others have pointed out above, it's okay if you only ever turn on one at a time. You'll run into trouble if you try to turn on more than one at a time.
    $endgroup$
    – Toor
    4 hours ago










1




1




$begingroup$
even though they have different +ve signal source?
$endgroup$
– DonP
4 hours ago




$begingroup$
even though they have different +ve signal source?
$endgroup$
– DonP
4 hours ago












$begingroup$
As the others have pointed out above, it's okay if you only ever turn on one at a time. You'll run into trouble if you try to turn on more than one at a time.
$endgroup$
– Toor
4 hours ago






$begingroup$
As the others have pointed out above, it's okay if you only ever turn on one at a time. You'll run into trouble if you try to turn on more than one at a time.
$endgroup$
– Toor
4 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%2f424033%2fcan-i-use-a-single-resistor-for-multiple-led-with-different-ve-sources%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

How to label and detect the document text images

Image
1 $begingroup$ This is what I mean as document text image: I want to label the texts in image as separate blocks and my model should detect these labels as classes. NOTE: This is how the end result should be like: The labels like Block 1, Block 2, Block 3,.. should be Logo, Title, Date,.. Others, etc. Work done: First approach : I tried to implement this method via Object Detection, it didn't work. It didn't even detect any text. Second approach : Then I tried it using PixelLink. As this model is build for scene text detection, it detected each and every text in the image. But this method can detect multiple lines of text if the threshold values are increased. But I have no idea how do I add labels to the text blocks. PIXEL_CLS_WEIGHT_all_ones = 'PIXEL_CLS_WEIGHT_all_ones' PIXEL_C
Read more

Vallis Paradisi

Image
Coordinata: .mw-parser-output .geo-default,.mw-parser-output .geo-dms,.mw-parser-output .geo-dec{display:inline}.mw-parser-output .geo-nondefault,.mw-parser-output .geo-multi-punct{display:none}.mw-parser-output .longitude,.mw-parser-output .latitude{white-space:nowrap} 33°03′S 71°37′W  /  33.05°S 71.617°W  / -33.05; -71.617 Vallis Paradisi Res apud Vicidata repertae: Civitas : Chilia Numerus incolarum : 296 655 Zona horaria : UTC-4 Situs interretialis Nomen officiale : Valparaíso Gubernium Consilium : municipal council of Valparaíso Geographia Superficies : 401 600 000 Metrum quadratum Coniunctiones urbium Urbes gemellae : Ovetum , Badalona , Santa Fe , Ora longa , Sciamhaevum , Quantunia , Callao , Bat Yam , Melaka , Novorossiysk , Busan , Corduba , Odessa , Rosario , Malacca , Barcino , Soteropolis , Franciscopolis (California) , Guanajuato, Silao Tabula aut despectus Despectus in portum sinumque et urbem Vallis Paradisi Vallis Para
Read more

Tabula Rosettana

Image
Tabula multilinguis Rosettana in Museo Britannico ostenditur. Tabula Rosettana, [1] etiam titulo OGIS 90 agnita, est stela decreto de rebus sacris in Aegypto anno 196 a.C.n. lato inscripta. Tabula iuxta Rosettam Aegypti, urbem in delta Nili et ad oram maris Mediterranei iacentem, anno 1799 a milite Francico reperta est. Inventio stelae, linguis duabus scripturisque tribus inscriptae, eruditis Instituti Aegypti statim nuntiata est; ibi enim iussu imperatoris Napoleonis eruditi omnium scientiarum (sub aegide Commissionis Scientiarum et Artium) properaverant cum expeditione Francica. Qua a Britannis mox debellata, tabula Rosettana Londinium missa hodie apud Museum Britannicum iacet. Textus Graecus cito lectus interpretationi textuum Aegyptiorum (in formis hieroglyphica et demotica expressorum) gradatim adiuvit. Denique textum plene interpretatus est Ioannes Franciscus Champollion. Ab opere eruditorum cumulativo coepit hodiernus scripturae hieroglyphicae linguaeque Aegyptiae a
Read more