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Can I use a single resistor for multiple LED with different +ve sources?
Why would an IR remote circuit use one resistor/transistor pair for each LED?Multiple LED over Serial communication with ArduinoWhich resistor to use for this LEDCan two LED circuits with a shared ground use a single resistor?Choose the right resistor for your RGB led (calibrate the colors)How can I use multiple Arduino-read photo resistors without interference between them?Common current limit resistor for multiple LEDs?Controlling individual LED strips of different kinds and lengths with a single microcontrollerWhy do people use a separate current limiting restore for each LED in a matrix?Basic resistor question for parallel LED circuit
$begingroup$
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?
arduino microcontroller led
asked 37 mins ago
DonPDonP
257
$endgroup$
add a comment |
$begingroup$
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?
arduino microcontroller led
asked 37 mins ago
DonPDonP
257
$endgroup$
$begingroup$
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
34 mins ago
1
$begingroup$
Looks like Diode OR logic ;) but problematic due to sharing current and voltage drop.
$endgroup$
– Sunnyskyguy EE75
27 mins ago
add a comment |
$begingroup$
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?
arduino microcontroller led
asked 37 mins ago
DonPDonP
257
$endgroup$
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?
arduino microcontroller led
arduino microcontroller led
asked 37 mins ago
DonPDonP
257
asked 37 mins ago
DonPDonP
257
asked 37 mins ago
DonPDonP
257
asked 37 mins ago
DonPDonP
257
asked 37 mins ago
DonPDonP
257
257
$begingroup$
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
34 mins ago
1
$begingroup$
Looks like Diode OR logic ;) but problematic due to sharing current and voltage drop.
$endgroup$
– Sunnyskyguy EE75
27 mins ago
add a comment |
$begingroup$
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
34 mins ago
1
$begingroup$
Looks like Diode OR logic ;) but problematic due to sharing current and voltage drop.
$endgroup$
– Sunnyskyguy EE75
27 mins 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
34 mins 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
34 mins ago
1
1
$begingroup$
Looks like Diode OR logic ;) but problematic due to sharing current and voltage drop.
$endgroup$
– Sunnyskyguy EE75
27 mins ago
$begingroup$
Looks like Diode OR logic ;) but problematic due to sharing current and voltage drop.
$endgroup$
– Sunnyskyguy EE75
27 mins ago
add a comment |
2 Answers
2
active
oldest
votes
$begingroup$
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.
Figure 1. Variations in Vf with different colours of LEDs. Source: LED I-V curves.
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.
answered 33 mins ago
TransistorTransistor
85.1k784181
$endgroup$
$begingroup$
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
14 mins ago
$begingroup$
Correct, and I completely forgot to cover that in the answer. I'll add it in.
$endgroup$
– Transistor
11 mins ago
$begingroup$
OK. Will mark as answer. THanks for the detailed response.
$endgroup$
– DonP
10 mins ago
add a comment |
$begingroup$
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.
answered 34 mins ago
ToorToor
72219
$endgroup$
$begingroup$
even though they have different +ve signal source?
$endgroup$
– DonP
18 mins 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
11 mins ago
add a comment |
Your Answer
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
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.
Figure 1. Variations in Vf with different colours of LEDs. Source: LED I-V curves.
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.
answered 33 mins ago
TransistorTransistor
85.1k784181
$endgroup$
$begingroup$
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
14 mins ago
$begingroup$
Correct, and I completely forgot to cover that in the answer. I'll add it in.
$endgroup$
– Transistor
11 mins ago
$begingroup$
OK. Will mark as answer. THanks for the detailed response.
$endgroup$
– DonP
10 mins ago
add a comment |
$begingroup$
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.
Figure 1. Variations in Vf with different colours of LEDs. Source: LED I-V curves.
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.
answered 33 mins ago
TransistorTransistor
85.1k784181
$endgroup$
$begingroup$
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
14 mins ago
$begingroup$
Correct, and I completely forgot to cover that in the answer. I'll add it in.
$endgroup$
– Transistor
11 mins ago
$begingroup$
OK. Will mark as answer. THanks for the detailed response.
$endgroup$
– DonP
10 mins ago
add a comment |
$begingroup$
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.
Figure 1. Variations in Vf with different colours of LEDs. Source: LED I-V curves.
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.
answered 33 mins ago
TransistorTransistor
85.1k784181
$endgroup$
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.
Figure 1. Variations in Vf with different colours of LEDs. Source: LED I-V curves.
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.
answered 33 mins ago
TransistorTransistor
85.1k784181
edited 5 mins ago
answered 33 mins ago
TransistorTransistor
85.1k784181
answered 33 mins ago
TransistorTransistor
85.1k784181
answered 33 mins ago
TransistorTransistor
85.1k784181
85.1k784181
$begingroup$
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
14 mins ago
$begingroup$
Correct, and I completely forgot to cover that in the answer. I'll add it in.
$endgroup$
– Transistor
11 mins ago
$begingroup$
OK. Will mark as answer. THanks for the detailed response.
$endgroup$
– DonP
10 mins ago
add a comment |
$begingroup$
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
14 mins ago
$begingroup$
Correct, and I completely forgot to cover that in the answer. I'll add it in.
$endgroup$
– Transistor
11 mins ago
$begingroup$
OK. Will mark as answer. THanks for the detailed response.
$endgroup$
– DonP
10 mins 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
14 mins 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
14 mins ago
$begingroup$
Correct, and I completely forgot to cover that in the answer. I'll add it in.
$endgroup$
– Transistor
11 mins ago
$begingroup$
Correct, and I completely forgot to cover that in the answer. I'll add it in.
$endgroup$
– Transistor
11 mins ago
$begingroup$
OK. Will mark as answer. THanks for the detailed response.
$endgroup$
– DonP
10 mins ago
$begingroup$
OK. Will mark as answer. THanks for the detailed response.
$endgroup$
– DonP
10 mins ago
add a comment |
$begingroup$
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.
answered 34 mins ago
ToorToor
72219
$endgroup$
$begingroup$
even though they have different +ve signal source?
$endgroup$
– DonP
18 mins 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
11 mins ago
add a comment |
$begingroup$
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.
answered 34 mins ago
ToorToor
72219
$endgroup$
$begingroup$
even though they have different +ve signal source?
$endgroup$
– DonP
18 mins 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
11 mins ago
add a comment |
$begingroup$
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.
answered 34 mins ago
ToorToor
72219
$endgroup$
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.
answered 34 mins ago
ToorToor
72219
answered 34 mins ago
ToorToor
72219
answered 34 mins ago
ToorToor
72219
answered 34 mins ago
ToorToor
72219
72219
$begingroup$
even though they have different +ve signal source?
$endgroup$
– DonP
18 mins 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
11 mins ago
add a comment |
$begingroup$
even though they have different +ve signal source?
$endgroup$
– DonP
18 mins 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
11 mins ago
$begingroup$
even though they have different +ve signal source?
$endgroup$
– DonP
18 mins ago
$begingroup$
even though they have different +ve signal source?
$endgroup$
– DonP
18 mins 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
11 mins 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
11 mins ago
add a comment |
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$begingroup$
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
34 mins ago
1
$begingroup$
Looks like Diode OR logic ;) but problematic due to sharing current and voltage drop.
$endgroup$
– Sunnyskyguy EE75
27 mins ago